The Journal for Equine Nutrition - Spring '22 Page 4

Issue 4 The Journal for sPRING 2022 Equine Nutrition NUTRIENT SPOTLIGHT: VITAMIN E Anouk Frieling MSc BSc (Hons) insect bite hypersensitivity: overview, management and future treatment Rebecca Allan equine metabolic syndrome Alison Morris BSc (Hons) the role of electrolytes in the exercising horse Dr. Femke Schaafstra nutrition of the stallion Anouk Frieling MSc BSc (Hons) PB 1The Journal for Equine Nutrition is FREE. To get every edition of The JEN to your inbox for free, sign up today at feedmark.com/JEN You will receive no marketing literature, and you will be the first to receive The JEN! Editor Contact us Dr Stephanie Wood 01986 782368 [email protected] [email protected] Feedmark Ltd, Church Farm, St Cross South Contributors Elmham, Harleston, Norfolk, IP20 0NY With special thanks to Alison Morris, Anouk Frieling, Dr. Femke Schaafstra and Rebecca Allan Whilst every care has been taken in compiling this publication Production & Design The JEN shall not be made liable for any inaccuracies therein. Gemma Hill The opinions expressed in this publication are not necessarily [email protected] those of the Editor/Publisher. 2 3Welcome I am really pleased to welcome you to the spring issue of Equine Lecturer at the College of Agriculture, Food and the JEN. We made it through the long winter and can now Rural Enterprise (CAFRE), unwraps this complex topic feel the slightly warmer temperatures, see the longer days and provides practical advice that I am sure you will find and watch new growth sprouting up everywhere. Often useful. This is the first of a series of articles on metabolic spring is thought of as a transitional season between the related issues which will run over the coming issues of the dominant winter and summer, with owners making plans JEN. for the summer ahead or simply reviewing how best to The next article focusing on the role of electrolytes in manage and support their horses. In the last issue of the exercising horses is key as the weather gets warmer and JEN I wrote about regularly evaluating your horse’s feeding horses sweat more. Dr. Femke Schaafstra, Senior Lecturer programme, and for many now will be a good time to do in Animal Nutrition at HAS University of Applied Sciences this. For horses and ponies affected by seasonal issues this in the Netherlands, provides a thorough review covering is particularly relevant, as often early intervention is key the purpose and importance of electrolytes, along with how to minimising problems. This issue of the JEN provides best to replace these essential nutrients that can be lost in practical suggestions and supportive information at what R considerable quantities when sweating rates are high. The EP can be a challenging time. A final article in this spring issue written by Anouk Frieling P D The first article written by Anouk Frieling, Feedmark’s focuses on nutrition of the stallion. Stallions performing EL Senior Nutritionist, takes an in-depth look at Vitamin E and multiple coverings on a daily basis are working hard and CYC many of its benefits. Anouk explores the different forms of their nutrition not only influences their general health, but ER vitamin E and the beneficial effects of this antioxidant, with also their fertility and breeding success. Anouk outlines key %0 the feeding of higher levels being particularly beneficial for nutrients and reviews how to optimise fertility with specific 01 exercising horses and breeding stock, making it a key nutrient dietary additions, making it an interesting read even for NO to review at this time. The second article on insect bite those not involved with breeding. DE hypersensitivity, also known as sweet itch, is also extremely T I hope this issue brings you helpful, practical advice at a NI timely. Rebecca Allan, Assistant Nutritionist at Feedmark, R time when lots of changes take place. P outlines the body’s allergic reaction and discusses options for managing this debilitating condition. Another concern many owners have all year round, but which is heightened at this time of year, is how best to support horses and ponies Dr. Stephanie Wood with Equine Metabolic Syndrome. Alison Morris, Senior Editor CONTENTS 4 22 Nutrient spotlight: Vitamin E The role of electrolytes in the exercising horse 10 28 Insect bite hypersensitivity: overview, Nutrition of the stallion management and future treatment 34 17 Glossary Equine metabolic syndrome 2 3Nutrient spotlight: Vitamin E Anouk Frieling MSc Equine Sciences, BSc (Hons) VITAMIN E STRUCTURE Vitamin E is a lipid-soluble antioxidant, synthesised by plants through photosynthesis (Reboul, 2017), that has Vitamin E is a term used for eight molecules with a multifunctional purposes in the body (Rigotti, 2007; Traber similar structure, four tocopherols and four tocotrienols & Head, 2021). It was discovered in 1922 during a study (Schneider, 2005). Tocopherols consist of one chromanol in rats where it was identified as an important element ring and a saturated phytyl tail whereas tocotrienols consist of a chromanol ring and an unsaturated isoprenyl tail with for reproductive processes in the body (Traber, 2007). three double bonds (Lee & Han, 2018; Niki & Abe, 2019) Further research throughout the years discovered the other (Figure 1). These forms of Vitamin E are designated into α, β, important functions Vitamin E has in the body, such as ƴ and δ depending on the location and number of the methyl supporting the immune system, liver function and muscle group (CH3) on the chromanol ring (Niki & Abe, 2019). health (Finno & Valberg, 2012). It was also suggested For example, the α-form of tocopherol and tocotrienol has that Vitamin E deficiencies are related to various health two methyl groups on R1, R2 and R3 (Figure 1) (Brigelius- issues and diseases in the horse (Finno and Valberg, 2012). Flohé, 2006; Niki & Abe, 2019). Each of the subgroups Therefore, this article highlights the importance of Vitamin (α, β, ƴ and δ both in tocopherols and tocotrienols) exist Tail E in the horse’s diet by explaining the different types of in eight different forms known as stereoisomers, with the α-form of tocopherol being the form of Vitamin E we are Vitamin E and the different functions it has in the body. Figure 1. The structures of the two different types of vitamin E, tocopherol and tocotrienol. The green hexagon displays the structure of the chromanol ring. A saturated phytyl tail is attached to the chromanol ring of the tocopherol and an unsaturated isoprenyl tail is attached to the tocotrienol chromanol ring. The table includes the different placements and amounts of methyl groups which translates in the different tocopherol and tocotrienol forms. (Adapted from Lee & Han, 2018) 4 5most interested in from a nutritional point of view. As such, et al., 2002; Lodge, 2005; Cheng et al., 2016), therefore this article will focus on α-tocopherol. the bioavailability of the synthetic Vitamin E is lower in Tocopherols contain three chiral carbons: one on C2 of comparison to the natural form (Vagni et al., 2011). This the chromanol ring and two on the tail at C4 and C8 (Figure means that a larger amount of natural Vitamin E is absorbed 2) (Niki & Abe, 2019). Each of these chiral carbons can be by the body in comparison to synthetic Vitamin E, even if configured in either the R configuration or S configuration. both types of Vitamin E are presented in similar amounts This means that there are eight possible configurations of Vitamin E is a lipid-soluble antioxidant, synthesised tocopherols (RRR, RRS, RSS, RSR, SSS, SSR, SRR and in the diet (Cheng et al., 2016). Therefore, natural Vitamin by plants through photosynthesis (Reboul, 2017), that has SRS), with each configuration representing the R or S E is suggested to have more effect on the body and is also multifunctional purposes in the body (Rigotti, 2007; Traber configuration of each of the three chiral carbons (Vagni et more efficient than synthetic Vitamin E as the body is more al., 2011). & Head, 2021). It was discovered in 1922 during a study likely to absorb and transport a higher concentration of in rats where it was identified as an important element The tocopherol configuration is important as enzymes and natural Vitamin E (Clemente et al.,2015). proteins within the body have evolved to work specifically for reproductive processes in the body (Traber, 2007). Further research throughout the years discovered the other important functions Vitamin E has in the body, such as supporting the immune system, liver function and muscle health (Finno & Valberg, 2012). It was also suggested that Vitamin E deficiencies are related to various health REP issues and diseases in the horse (Finno and Valberg, 2012). AP Therefore, this article highlights the importance of Vitamin D Tail EL E in the horse’s diet by explaining the different types of CY Vitamin E and the different functions it has in the body. CER %00 Figure 2. Natural vitamin E and synthetic vitamin E structure showing configuration R on 2', 4' and 8' of natural vitamin E and R or S configuration on 1 the structure of synthetic vitamin E. NO DET VITAMIN E DIGESTION AND ABSORPTION with certain configurations. The RRR configuration is NI produced naturally in plants, therefore the most natural and R It is suggested that the digestion of Vitamin E starts in P abundant form of Vitamin E is RRR-α-tocopherol (Herrera the duodenum, part of the small intestine, as the stomach is & Barbas, 2001; Niki & Abe, 2019). thought to have no significant effect on Vitamin E digestion (Borel et al., 2001). In the duodenum digestive enzymes NATURAL AND SYNTHETIC VITAMIN E such as proteases, amylase and lipases mix with the food Vitamin supplements can consist of two types of Vitamin and release Vitamin E (Borel et al., 2013). Vitamin E that E, natural or synthetic Vitamin E (Finno & Valberg, is not already incorporated into vegetable oils is transferred 2012). Synthetic Vitamin E contains equal proportions into micelles in combination with dietary fats (Rich et of all eight stereoisomers and therefore contains both R al., 2003; Borel et al., 2013). These micelles are thought or S configurations (Vagni et al., 2011). This means that to be essential for Vitamin E absorption (Reboul, 2017), synthetic Vitamin E contains 1/8th or 12.5%, natural RRR- which mainly takes place in the small intestine where it is α-tocopherol. There are two types of synthetic Vitamin E, suggested that α- and ƴ-tocopherols are absorbed in similar all-rac-α-tocopherol and dl-α-tocopherol (Finno & Valberg, amounts, depending on the concentration of the Vitamin 2012), with all-rac-α-tocopherol acetate being the most E forms in the diet (Rigotti, 2007). After absorption the common form used in supplements (Vagni et al., 2011). Vitamin E is then transported to the liver where it is stored Previous human and animal studies, including horses for further use (Rigotti, 2007). When Vitamin E is required by the body it is secreted into the circulation from the liver, (Fiorellino et al., 2009; Fagan et al., 2020), have shown bound to a very-low-density lipoprotein (VLDL), which is that the body favours the natural variant of Vitamin E (RRR required to transport the Vitamin E to different target cells form) over the synthetic form of Vitamin E (Lauridsen 4 5is increased that this has a significant effect on the immune (Di Donato et al., 2010). Even though α- and ƴ-tocopherols response (Meydani et al., 1990; Han & Meydani, 1999). are absorbed in similar amounts, in rat studies RRR-α- For example, a study in horses demonstrated a connection tocopherol was found to be more frequently transported between an increased immune response, measured through through the body after absorption in comparison to other an increase of the antibody Immunoglobin G (IgG), and an Vitamin E forms, suggesting that the natural form of Vitamin increased supplementation of Vitamin E or a combination E is the favoured form by the body (Ikeda et al., 1996). of Vitamin E and Selenium after horses were given a Natural Vitamin E is most likely favoured by the body due tetanus or equine influenza vaccination (Baalsrud & to α-tocopherol transfer protein (α-TTP), a liver protein, Øvernes, 1986). Another study showed that administration which binds Vitamin E to VLDLs (Di Donato et al., 2010). of 2500IU of RRR-α-tocopherol per day to pregnant mares It is suggested that α-TTP selectively favours α-tocopherols increased the antibody concentration of IgG and IgM in in comparison to other Vitamin E forms (Di Donato et al., colostrum which resulted in a higher IgM concentration in 2010). Based on the body’s response to different Vitamin E blood plasma of the foals (Bondo & Jensen, 2011). This forms, horses requiring higher levels of Vitamin E, such as increased concentration supports the foal’s immune system those with muscle, liver or immunity issues, are likely to and improves protection against infectious diseases after benefit from being fed natural Vitamin E. birth (Bondo & Jensen, 2011). Therefore, it is suggested FUNCTIONS OF VITAMIN E that Vitamin E enhances immunity and increases pathogen An imbalance of production and accumulation of oxygen resistance in the body (Meydani et al., 2005). reactive species (ROS) can create free ranging free radicals As mentioned previously, Vitamin E was discovered due in the body (Pizzino et al., 2017). A free radical is a molecule to its effects on reproductive processes in the rat (Traber, or atom that has an odd number of electrons and therefore 2007). Oxidative stress can also affect reproductive the atom or molecule becomes instable (Phaniendra et processes in horses, such as oocyte maturation, spermatozoa al., 2015). To become stable the free radicals react with function and pregnancy, and can therefore cause infertility biochemicals in the body to gain electrons to create an even in mares and stallions (Finno & Valberg, 2012). The effects number, therefore the biochemical becomes a free radical of Vitamin E supplementation on stallion fertility has been as it then has an odd number of electrons (Phaniendra analysed in previous studies, showing a significant positive et al., 2015). This chain reaction can create damaging effect of supplementation of 3000IU Vitamin E per day oxidative stress to cells and tissues in different parts of the on the fertility of stallions (Gee et al., 2008). For more body (Pizzino et al., 2017; Garcia et al., 2022). The main information about the effects of Vitamin E supplementation function of the antioxidant Vitamin E is to bind to these free on stallion fertility please refer to Nutrition of the stallion. radicals and neutralise them to prevent them from creating It is clear that a Vitamin E deficiency can result in infertility oxidative stress (Fagan et al., 2020). Oxidative stress can in males and females (Rengaraj & Hong, 2015), which is for example affect the liver, which has many functions why supplementation is suggested for breeding stock that within the body, including the storage and transportation receives a diet that does not provide the required daily of Vitamin E (Singal et al., 2011). Therefore, Vitamin E Vitamin E. supplementation can offer support to animals with liver diseases due to oxidative stress (Bansal et al., 2005; Singal Oxidative stress is suggested to increase during heavy et al., 2011; Tallon & McGovern, 2020). The Vitamin E exercise which can have an effect on the muscles as it requirement of a healthy adult horse fed equivalent to 2% can result in muscle tissue damage (Kinnunen et al., of their body weight per day as fibre, is between 1 and 2IU 2005). Because of the multiple functions of Vitamin E, per day/kg body weight depending on the horse’s workload it is suggested that Vitamin E supplementation can have (NRC, 2007). It is recommended to feed two to three times an effect on oxidative stress in heavily exercised horses this amount to horses affected by liver issues as this amount and will reduce the risk of muscle damage (Williams & is likely to be beneficial (Carr & Holcombe, 2009). Carlucci, 2006; Fagan et al., 2020). Research investigating the effects of Vitamin E on oxidative stress in horses Free radicals are able to damage immune cells since performing exercise has shown contrasting results. they are prone to oxidative damage (Coquette et al., McMeniman & Hintz (1992) and Williams et al. (2004) 1986; Meydani et al., 2005). Studies in animals and were unable to identify significant effects after Vitamin E humans have shown that when the daily Vitamin E intake 6 7concentrations in the skeletal muscle fibres of the horse supplementation on oxidative stress post heavy exercise, and accumulation of glycogen (Nollet & Deprez, 2005). whereas more recent research suggested that Vitamin E Polysaccharide storage myopathy occurs in two variants, has the potential to decrease oxidative stress in heavily type I and type II (Valberg, 2014). Polysaccharide storage exercised horses (Fagan et al., 2020). Fagan et al. myopathy type I is mainly found in draft horses and Quarter (2020) fed adult horses, performing heavy exercise and Horse related breeds. Type I is connected to a mutation on weighing approximately 550kg, 4000IU Vitamin E per the glycogen synthase gene (GYS1) in horses (Stanley et day. This is considerably higher than current NRC (2007) al., 2009) (Stanley et al., 2009), and therefore the disease recommendations of 1000IU Vitamin E per day for a 500kg can be diagnosed by performing a genetic test. The clinical horse performing such exercise, showing the importance symptoms are related to rhabdomyolysis (tying-up) and of continued research into equine nutrition and updating of occur when the horse performs exercise (Firshman et recommendations. al., 2005). If the horse starts showing clinical symptoms VITAMIN E DEFICIENCY AND HEALTH ISSUES related to PSSM regularly the horse owner is advised not In horses there are diseases related to consistent Vitamin to exercise the horse for an extended period, however due E deficiency in the body; tying-up, polysaccharide storage to the genetic mutation clinical signs will reappear as soon myopathy (PSSM), equine motor neuron disease (EMND), as the horse starts exercising again (Firshman et al., 2005). equine degenerative myeloencephalopathy (EDM) and Horses with PSSM type II show the same muscle glycogen Vitamin E deficient myopathy (Finno & Valberg, 2012). abnormalities and the accompanying clinical signs but lack R Tying-up, also called rhabdomyolysis, is a disease which the mutation on GYS1, and therefore the specific cause EP affects the muscles and can occur sporadically or chronically A of PSSM type II is not known (Williams et al., 2018). In P (Tozaki et al., 2010). The chronic form of tying-up is called comparison to type I, type II mainly occurs in Warmblood DEL polysaccharide storage myopathy (PSSM) (Valberg, 2014). and Thoroughbred horses (Valberg, 2014). It is advised that CY Tying-up can be caused due to respiratory infections, the diet of horses with PSSM or tying-up is supplemented CE exhaustive and excessive training, or it can be caused due with additional fat as it is suggested to act beneficially R % to a lack of Vitamin E and Selenium in the horses diet for horses with this disease. Because of the high-fat diet 00 (Valberg, 2014). Signs of tying-up are muscle stiffness, 1 it is suggested to supplement the diet with 600 to 6000IU N discomfort when moving, muscle contractions such as Vitamin E per day to support muscle health (Mckenzie et O muscle spasm in the hindquarters, and an elevated heart D al., 2002; Williams, 2008). ET rate (Bouwman et al., 2010). N Equine motor neuron disease (EMND) is a disease IR Polysaccharide storage myopathy (PSSM) is a muscle P affecting the somatic lower motor neurons and ventral disorder and was first recognised in Quarter Horses (Valberg horns of the spinal cord and selected brain stem nuclei, et al., 1999). This disease causes abnormal polysaccharide caused by prolonged and consistent Vitamin E deficiency Anouk Frieling, MSc Equine Sciences, BSc (Hons) Anouk has been involved with horses from a young age. During her time taking care of horses on yards and during the undergraduate Animal Husbandry at HAS University of Applied Sciences in the Netherlands, she developed an interest for equine nutrition. To gain more specific knowledge about equine nutrition she completed the MSc Equine Sciences at Aberystwyth University. As Senior Nutritionist at Feedmark, Anouk provides information that combines her technical knowledge and practical experience obtained from her studies and taking care of many different types of horses. 6 7supplementation of Vitamin E is suggested to decrease the (Cummings et al., 1990). This disease can only be severity of the symptoms (Finno & Valberg, 2012; Burns & diagnosed post-mortem but clinical signs are weight loss Finno, 2018). due to muscle wasting, muscle twitching and horses lying down for prolonged periods (Divers et al., 1994). The SUMMARY affected neurons are suppliers of type I muscle fibres which Vitamin E is an antioxidant with multiple functions are responsible for slow muscle contractions and are highly in the body and is therefore an important vitamin in the resistant against fatigue (Finno & Valberg, 2012; Ciciliot horse’s diet. Natural Vitamin E (RRR-α-tocopherol) is et al., 2013). Therefore, the muscle fibre supply is also the most abundant Vitamin E form and is also the most affected by EMND (Finno & Valberg, 2012). This disease bioavailable form of Vitamin E. Horses mainly derive is mainly found in horses that have no access to pasture Vitamin E from fresh forage from pasture, therefore it is and/or fresh forage, as fresh pasture is normally the main advised to supplement Vitamin E to horses if they have Vitamin E supplier in the horse’s diet (Divers et al., 1994). little to no access to pasture. Equine Vitamin E supplements Therefore, it is recommended to supplement Vitamin E to either contain natural or synthetic Vitamin E, which have horses which are not able to graze on pasture (Finno & Valberg, 2012) and if EMND is suspected it is suggested to similar structures but have different configurations, supplement the feed of a 500kg horse with 5000IU per day with natural Vitamin E having greater bioavailability in for a prolonged period (Naylor, 2014). comparison to synthetic Vitamin E. Natural Vitamin E has Equine degenerative myeloencephalopathy (EDM) is greater bioavailability as the body favours this form over a genetic neurodegenerative disease related to Vitamin other Vitamin E forms and therefore, natural Vitamin E is E deficiencies (Burns & Finno, 2018). One of the absorbed in higher concentrations. The main function of most significant clinical signs is development of ataxia Vitamin E is to neutralise free radicals in the body which (uncoordinated movement) during the first year of the are created due to oxidative stress. Increased Vitamin E supplementation is also known to support liver function, muscle tissue, reproductive functions and increased immune responses to prevent diseases and infections. The Vitamin E requirements of a healthy horse are between 1 and 2IU per day/kg body weight, which can differ depending on workload. It is recommended to increase the daily natural Vitamin E intake by two to three times to support horses with liver issues. A study has shown that to support the immune system Vitamin E intake can be increased to 2500IU/day and to support fertility it can be increased to 3000IU/day. Horses that are affected by muscle issues or that perform heavy exercise and therefore Figure 3. The large muscles of the back and hindquarters of horses need muscle health support can benefit from an increased that are affected by a muscle disorder show signs of weakness Vitamin E intake up to 4000IU per day. Prolonged Vitamin or cramping. These clinical signs can be supported by feeding E deficiencies can cause disorders such as tying-up, additional dietary Vitamin E. equine motor neuron disease and equine degenerative horse’s life (Burns & Finno, 2018). Other clinical signs myeloencephalopathy. Polysaccharide storage myopathy are that the horse seems to overshoot where they place is also a muscle disease and a form of tying-up that can their limbs (hypermetria) when being walked with an be related to a genetic mutation. Increased Vitamin E elevated head, and an abnormal stance at rest. Some supplementation is beneficial for horses that are affected by affected horses also seem to have a decreased fight or flight these disorders. In conclusion, Vitamin E is an important response (Aleman et al., 2011; Burns & Finno, 2018). It is nutrient in the horse’s diet, and it is therefore important to suggested that the disease is related to a decreased level of meet the daily requirements by providing a tailored diet. α-tocopherol in the first four months of a horse’s life (Burns For extra support the daily amount can be increased by & Finno, 2018). This disease cannot be treated but the providing a (natural) Vitamin E supplement. 8 9REFERENCES Aleman, M., Finno, C. J., Higgins, R. J., Puschner, B., Gericota, B., Gohil, K., LeCouteur, R. A. & Madigan, J. E. (2011) Evaluation of epidemiological, clinical, and pathological features of neuroaxonal dystrophy in Quarter Horses. Journal of the American Veterinary Medical Association, 239(6): 823-833. Baalsrud, K. J. & Øvernes, G. (1986) Influence of vitamin E and selenium supplement on antibody production in horses. Equine Veterinary Journal, 18(6): 472-474. Bansal, A. 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PLoS ONE, 13(9): 1-17. 8 9Insect bite hypersensitvity: overview, management and future treatment Rebecca Allan Equids live in an environment shared with different mouthparts are greatly reduced so generally do not carry species and are exposed to several external irritants from out bloodsucking behaviour and therefore are not thought which skin conditions can arise. Insect bite hypersensitivity to cause IBH (Mullen et al., 2019). Nevertheless, it is (IBH) is an allergic skin disease in horses, and is a relapsing the saliva passed through by their blood sucking feeding condition caused by the Culicoides species of biting midges mechanism that induces IBH in horses. (Papadopoulos et al., 2010). The first case was reported in It is also thought that black flies of the species Simulium France in 1840 and by the published research of Henry and Vittaum may cause IBH. This was determined through Borey (1937), it was named ‘dermatose estivale récidivante antigen stimulation testing through which affected horses du cheval´, meaning ‘recurrent summer dermatosis reacted to extracts from Simulium Vittaum, leading to the of the horse´. Since then, this condition has become a view that they may share similar allergens as Culicoides, worldwide issue and has developed different terminologies and therefore be a potential cause of IBH, although more such as sweet itch, Queensland itch, summer eczema or studies need to confirm this (Baselgia et al., 2010). seasonal dermatitis, names which vary depending on your INSECT BITE HYPERSENSITIVITY - PATHWAY geographical location (Pooley, 2005). Any equine breed As is assumed, the saliva from the bite of Culicoides can succumb to the condition, with the prevalence of this midge is an allergen, which means the saliva contains a disease estimated at 3-10% across Europe (Birras et al., protein which triggers an allergic/ hypersensitivity reaction 2021). In mainland UK, the onset of sweet itch is prevalent between April and the beginning of December (Baker et in the host (in this case the horse) (Langner, et al., 2009). al., 1978) however in European countries where a warmer The onset of these reactions is caused by the equine’s climate is present this disease can take place at any time immune system to aid recovery. Therefore, to understand of year. the complexity of the disease it is important to understand the physiological responses taking place within the CULICOIDES MIDGE horse’s body. The most common species inducing IBH is the Culicoides Immune system hypersensitivity reactions can which belongs to the family Ceratopogonidae (Papadopoulos be broadly classified in two main groups: antibody- et al., 2010). They are small insects comprising of two mediated reactions and T-lymphocyte mediated reactions wings with an elongated thorax and segmented abdomen (Swiderski, 2000). An antibody is a protein used by the which ranges between approximately 1.0-2.5mm in length. body to identify and neutralise foreign objects (in this case Interestingly, due to their small size they are also known allergens from the Culicoides saliva) (Swiderski, 2000), as no-see-ums as they generally go unnoticed and are not whilst a T-lymphocyte is a type of white blood cell that easily seen (Mullen et al., 2019). Female mouthparts are has a number of key roles in horse’s immune responses well adapted for biting and piercing tissues. They also have (effectively fighting the allergen). a longitudinal groove through which saliva passes whilst Hypersensitivity reactions are categorised into different they feed on vertebrate blood. Generally, the females types, dependant on the immune responses triggered. require vertebrate blood for reproductivity purposes. Males Originally IBH was classified as a Type I hypersensitivity on the other hand, differ slightly in morphology as their 10 11reaction however recent studies have also shown Type IV As can be seen in Table 1, it is a combination of these hypersensitivity reactions to be involved. immunological pathways caused by the saliva of the midge Type I hypersensitivity reactions, also known as which start off the disease internally and leads to the immediate reactions, are antibody mediated and involve external clinical signs presented by affected horses Table 1. Summary of hypersensitive reactions in IBH affected horses (Swiderski, 2000, Wagner et al., 2006) Hypersensitivity type Name Immune response Signs after exposure Pathogenesis I Immediate IgE antibody 15min Allergic inflammatory hypersensitivity responses IV Delayed type T cells, Cytokines More than 24hr hypersensitivity CLINICAL SIGNS immunoglobulin E (IgE) antibodies. These antibodies act within 15 minutes of the allergen’s presence by binding As described in the immunological pathway of IBH, to receptors on mast cells and basophils which release inflammation is the internal primary response leading histamine, finally recruiting eosinophils (white blood R to the condition. This initial inflammation to the allergic EP cells) to the allergic site, and consequently producing an A site consequently leads to irritation which results in the P inflammatory response (Wagner et al., 2006, Fettelschoss- D common clinical signs equines affected with this disease EL Gabriel et al., 2018). C present (MacKay, 2000). Y From investigations via intradermal testing, it was also C Baker et al. (1978) performed a study to determine the ER noted that horses suffering from IBH recruited T helper clinical aspects and histopathology of sweet itch. Fifteen %0 cells (Th2 cells) and eosinophils to the injection site. As 0 affected horses were examined clinically by analysing skin 1 Type IV hypersensitivity is characterised by T-lymphocyte N scrapings. The age of the horses used in the study ranged O mediated reactions, this study confirmed the presence of D from 18 months to 20 years old, meaning the results are ET Type IV hypersensitivity reactions in horses suffering N applicable to a wide range of horses. Furthermore, the I from IBH. However, Type IV reactions are divided into 4 RP study took place from the end of April to the beginning subclasses, and due to the Th2 cells involved, it is subclass of December, prime time for sweet itch to occur. Results Type IVb reactions involved in IBH (McKelvie et al., showed clinical signs to be mainly pruritic (intense itching) 1999, Fettelschoss-Gabriel et al., 2018). Type IV reactions with localised alopecia (hair loss), as well as evidence of are also known as delayed reactions and can occur 24hr skin abrasions. Additionally, horses who were commonly after allergen exposure. In IBH, Th2 cells act by producing affected by the disease presented complete loss of hair over cytokines such as interleukin-5 (IL-5). The IL-5 cytokine lesioned areas and rigid skin was noticed. The mane and targets and attracts eosinophils to the allergic site which top third of the tail were commonly affected and mostly all together results in the production of inflammatory de-haired (Figure 1). Björnsdóttir et al. (2006) supports responses (Spencer & Weller, 2010, Fettelschoss-Gabriel these findings, reporting that the mane (93%) and the tail et al., 2018). When activated, eosinophils also release (72%) were the most affected areas in sweet itch horses, effector molecules such as histamine which have the with the abdomen, head, side of the body, and chest also effect of enhancing allergic responses that can cause tissue being affected, although to a lesser extent. It is to note, damage (McKelvie et al., 1999, Fettelschoss-Gabriel et al., these clinical signs are a result of self-inflicted trauma as 2018). Thus, making eosinophils a key cell type in IBH allergic responses as they are present in both Type I and the horse tries to alleviate itself by itching. Additionally, Type IV reactions. secondary infections from other parasites such as mites 10 11al., 2021). A positive result to the allergen would result in an inflammatory flare response. Thus, if your horse’s skin flares to the Culicoides spp. extract there is a strong likelihood of your horse having IBH. MANAGEMENT AND PREVENTION Management of IBH is based on reducing exposure to the biting midge. At present there is no definitive cure for sweet itch. Therefore, management and prevention methods are key to reduce affected horses’ exposure to the biting midges. Culicoides midges are found worldwide, however they do have environmental and climate conditions which they favour. While biting midges have wings, they are poor flyers Figure 1. Common clinical signs presented by equines affected hence windy conditions do not favour their activity. As a by IBH general guideline, windless conditions with temperatures may arise and produce further irritation, perpetuating lesion above 10℃ are ideal for their activity (Barbet, 2014). They formation (Hastie, 2012). also favour moist and humid surfaces such as moist mud, as this is where the females lay their eggs (Mullen et al., DIAGNOSIS 2019). In practical terms, areas near water buckets, water The most common diagnosis for IBH is via visual throughs, streams and ponds which have moist terrain assessment of the clinical signs presented by the horse. nearby, are the areas where midges are going to thrive, However, for further clarification and examination, although midges can travel up to 2km from their breeding intradermal tests are carried out by veterinary professionals. ground, meaning their source may not be obvious, and Intradermal tests use extracts of environmental therefore more challenging to avoid (Mullen et al., 2019). substances (in this case Culicoides extract) which are then By knowing the midge’s activity, a management and injected into the dermis of the skin at specific volumes and prevention plan can be thought out. It is also of high concentrations (Figure 2). Injection sites are then assessed importance to be proactive and start these measures before for a response, with the classic response being a wheal- April to prevent the onset of sweet itch. and-flare response. The responses at the injection site are • As mentioned, midges thrive on moist and damp then measured at timed intervals such as at 30 minutes and conditions, such as near water throughs in fields at 4 hours post injection (Tahon et al., 2009, Lo Feudo et or on droppings. Therefore, removing faeces from fields should be regular practice and avoiding dampness near water buckets by not letting them overfill is advised. In addition, avoiding turning out near water sources such as ponds and streams is preferable if facilities allow. • Midges are most active during dusk and dawn, therefore preventing your horse from being turned out in the field during these times of day can help to Figure 2. Intradermal testing causing a wheal-and-flare response limit exposure. confirming IBH 12 13most effective insecticides available in the UK as results varied. Thus, this study provides evidence that fine netting in stables can help deter the biting midges. NUTRITIONAL SUPPORT As well as daily routine management and physical barriers such as rugs and stable nettings, soothing the itching to keep your horse as comfortable as possible is also beneficial. This can be achieved through nutritional Figure 3. Sweet itch rugs as a control method against midge bites supplementation providing support from the inside out to • Due to females laying their eggs on damp surfaces optimise skin health. and midges generally being poor flyers – exposed Dietary supplementation with essential fatty acids (EFAs) well drained fields for your horse’s turnout are the may be useful in equine allergic conditions. Essential fatty best option. acids are known to be crucial in maintaining skin barrier As well as daily yard management, sweet itch rugs can function and have a recognised role in inflammatory also help reduce horses’ exposure to the allergen. Sweet processes. Furthermore, Omega-3 fatty acids are especially RE itch rugs are designed with a fine mesh to prevent the midge renowned for their anti-inflammatory properties (Hess & PAP coming into direct contact with the horse, effectively acting Ross-Jones, 2014). Supplements high in Omega-3 fatty DE as a barrier (Figure 3). Sweet itch rugs also provide belly acids are those such as linseed oil, algae oil, and fish oils. LCY coverage which standard fly rugs do not offer. Although Linseed oil is high in alpha-linolenic acid which theoretically CE costly, sweet itch rugs can be of great help to manage R is converted to eicosapentaenoic acid (EPA) and possibly % the disease. 0 into docosahexaenoic acid (DHA) (Harper et al., 2006). 01 Furthermore, Baker et al. (2015) performed a study Thus, making it a suitable aid to support healthy skin tissue. NO to determine whether the addition of insecticide-treated However, according to Weldon et al. (2007), DHA is more DE netting (ITN) in stables could provide protection for horses T effective in reducing inflammation than EPA. For this NI from Culicoides spp. in the UK. It was concluded that R reason, algae oil is especially beneficial as it contains high P ITN of 1.6mm in aperture does have the potential to offer levels of DHA exhibiting potent anti-inflammatory actions protection from Culicoides midges and reduce the biting of (Nauroth, et al., 2010). Interestingly, a study by Elzinga et these insects. However, this study failed to conclude on the al. (2019) found DHA-rich microalgae supplementation to Rebecca Allan Rebecca moved to England from Spain in 2017 to further her education. While undertaking A levels, she completed BHS Qualifications where she developed a keen interest in equine health and nutrition. In 2019 Rebecca started a BSc (Hons) Veterinary Bioscience degree at the University of Surrey. Rebecca is currently on her placement year as an Assistant Nutritionist at Feedmark Ltd. Her aim is to qualify as a Veterinary Bioscientist and progress into Equine Nutrition in the future. 12 13have potential immune-modulating and anti-inflammatory actions (Bendich, 1993). A study conducted by Petersson properties for horses with Equine Metabolic Syndrome et al. (2010) found that Vitamin E supplementation of (EMS). Therefore, algae oil supplementation may help predominantly older horses enhanced their general cell- soothe and alleviate irritated skin as well as support the mediated immunity (immune response driven by T cells, immune system. cytokines, and macrophages) and humoral immune Vitamin E is recognised as a powerful antioxidant, functions (immune response mediated by antibodies). with human research indicating that it is regularly Vitamin E supplementation may therefore be particularly secreted on the facial skin surface, as this area is most beneficial for horse’s suffering from sweet itch to aid their exposed to environmental damage, and that it may play a overall immune system. pivotal role in the removal of free radicals from the skin, Herbal nutritional options to optimise skin health from Table 2. Herbal Remedies with their function and scientific evidence Herbal remedy Action Supporting evidence Marigold flowers Anti-inflammatory and Recommended for treatment for minor wounds and skin anti-bacterial properties inflammation (Nicolaus et al., 2017). Interestingly, farms (Parente et al., 2011) in Switzerland manufacture marigold flower ointments for overall skin health and wound repair of their livestock (Schmid, et al., 2012) Brewer's Yeast Brewer´s Yeast contains natural A study was conducted in humans who were administered B vitamins including Biotin, Brewer´s Yeast, which showed improvements in their skin which is essential for growth condition (Hibino et al., 2010). and maintenance of the skin tissues as well as for hoof growth support (Reilly et al., 1998). Burdock root/ Burdock root contains active A study performed in patients suffering from acne showed leaves ingredients which promote significant lesion improvements when supplemented with blood flow to the skin surface, burdock root for 6 months (Miglani et al., 2014). Furthermore, thus improving skin quality a study performed by nurses on burn wounds of Amish people, and texture (Chan et al., 2010). concluded trauma from dressing removals to be non-existent Whilst burdock leaves have using a paste containing burdock leaves on first- and second- analgesic and anti-inflammatory degree burns (Kolacz et al., 2014). Suggesting burdock leaves´ properties (Kolacz et al., 2014) soothing properties reduce discomfort. reducing cell damage and potentially benefiting skin health the inside out are also available. Table 2 offers some herbal (Thiele et al., 1999, Williams & Carlucci, 2006). A study options for optimum skin condition and to help alleviate conducted by Plevnik et al. (2014) on dogs suffering from itchiness, although herbal therapies are not limited to the atopic dermatitis, showed improved skin lesions in dogs herbs listed as there are many other herbs such as Nettle, supplemented with Vitamin E compared to those on the Clivers and Chamomile that can help soothe sensitive or placebo treatment. Improvement in the clinical signs such irritated areas. as excoriation (skin biting, chewing or licking) and alopecia FUTURE TREATMENT were noted after 8-weeks Vitamin E supplementation, Although currently a specific treatment has not been hence the view that Vitamin E may have beneficial effects established to deal with IBH, sweet itch has become a key on the skin's condition. research area, with studies showing that a vaccine may Vitamin E is also recognised for its immune-supporting 14 15effectively treat the condition. eosinophil counts and lesion scores as it was thought the As previously described, IBH involves Type I absence of IL-5 due to vaccination meant eosinophils did and Type IV hypersensitivity reactions. The Type IV not enter tissues. Alongside the internal response to the hypersensitivity reactions are characterised by Th2 cells vaccine, clinical signs of sweet itch also improved when which produce IL-5 cytokines attracting eosinophils, horses were vaccinated in comparison to the same horses creating an inflammatory response. Eosinophils account the previous season and with those horses on the placebo- for a large portion of the symptoms presented by IBH. controlled experiment. The benefit of this vaccine is that Due to these series of reactions, Fettelschoss-Gabriel et al. when administered, the antibodies are self-made by your (2018) decided to target the IL-5 cytokine as it is a master horse’s immune system meaning this vaccine can be regulator for eosinophils as it is in charge of eosinophils´ administered before the IBH season starts, so antibody survival, development, and activation. It was thought that production increases during IBH season and decreases blocking IL-5 cytokine would be a safe and efficient way again during unaffected times of year. in reducing eosinophil-mediated inflammation. Previous Overall, eIL-5-CMV is the first anti-cytokine TT studies using mice treated with IL-5 antibodies resulted vaccine to have shown clinical efficacy for the treatment in reduced blood eosinophils, meaning eosinophil counts of equine IBH disease. Targeting IL-5 cytokine limited R could be regulated by limiting IL-5 stimulation (Zou the development of eosinophils and the skins’ reaction, EPA et al., 2010). Also, studies in human patients suffering improving clinical signs. P D from eosinophilic-mediated diseases such as eosinophil- E SUMMARY LC mediated asthma and hyper-eosinophilia have also shown Y Insect bite hypersensitivity is a worldwide disease C positive results. Patients were treated with antibodies ER caused mainly by the saliva of female Culicoides species targeting IL-5 cytokine´s action, significantly reducing %0 of the biting midge. The onset of this disease is based 01 eosinophil counts. Due to this treatment, the clinical on the horse’s immune system exerting Type I and N signs presented by patients with inflammatory associated O Type IV hypersensitivity reactions which then induce D diseases were improved (Roufosse, 2018). Thus, these two ET inflammation at the allergic site. This inflammation then NI studies led to the investigations into the vaccine for horses. R triggers the presentation of external clinical signs, with P The vaccine was created on a novel, virus like particle the most common being intense itching and hair loss at (VLP) platform based on the cucumber mosaic virus. the base of the mane and tail. Insect bite hypersensitivity This contained the tetanus toxoid (inactivated toxin) can be determined through clinical signs but for further universal T cell epitope (specific part of the antigen evidence intradermal tests can take place. Management where the antibody binds itself to) also known as CMV . TT procedures to minimise the exposure of the biting midge CMV enhances T helper cell responses for antigens TT are key principles to control this disease as well as the displayed on the VLP surface. Thus, the vaccine consisted physical barriers such as sweet itch rugs and stable netting. of equine IL-5 (eIL-5) chemically linked to CMV - TT Likewise, nutritional supplementation also plays a crucial VLPs which induced anti-eIL-5 antibodies in horses role in soothing irritation and improving skin health, and so (Fettelschoss-Gabriel et al., 2018). in keeping horses comfortable. Furthermore, research has Icelandic horses suffering from IBH were used in the ) improves demonstrated that the vaccine (eIL-5-CMV Fettelschoss-Gabriel et al. (2018) study to trial the vaccine. TT clinical signs of IBH in affected horses by targeting IL-5 The results showed that the vaccine induced anti-IL-5 antibodies in horses and eosinophil-mediated symptoms cytokine, offering hope to the treatment and management were treated. There was no longer correlation between of this incurable disease. 14 15REFERENCES Baker, K.P. & Quinn, P.J., (1978). A Report on Clinical Aspects and Histopathology of Sweet Itch. Equine Veterinary Journal, 10 (4): 243-248. Baker, T., Carpenter, S., Gubbins, S., Newton, R., Lo lacono, G., Wood, J. & Harrup, L.E., (2015). Can insecticide-treated netting provide protection for Equids from Culicoides biting midges in the United Kingdom? Parasites & Vectors, 8: 604. Barbet, J.L., (2014). Chapter 59 - Ectoparasites of Horses. 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Tahon, L., Baselgia, S., Gerber, V., Doherr, M., Straub, R., Robinson, N. & Marti, E., (2009). In vitro allergy tests compared to intradermal testing in horses with recurrent airway obstruction. Veterinary Immunology and Immunopathology, 127(1-2): 85-93. Thiele, J. J., Weber, S.U., & Packer, L., (1999). Sebaceous gland secretion is a major physiologic route of Vitamin E delivery to skin. Journal of Investigative Dermatology, 113(6): 1006 – 1010. Wagner, B., Miller, W.H., Morgan, E.E., Hillegas, J.M., ERB, H.N., Leibold, W. & Antczak, D.F., (2006). IgE and IgG antibodies in skin allergy of the horse. Veterinary Research, 37(6): 813-825. Weldon, S.M., Mullen, A.C., Loscher, C.E., Hurley, L.A. & Roche, H.M., (2007). Docosahexaenoic acid induces an anti-inflammatory profile in lipopolysaccharide-stimulated human THP-1 macrophages more effectively than eicosapentaenoic acid. Journal of Nutritional Biochemistry, 18(4): 250-258. Williams, C. & Carlucci, S., (2006). Oral vitamin E supplementation on oxidative stress, vitamin, and antioxidant status in intensely exercised horses. Equine Veterinary Journal, 38(S36): 617-621. Zou, Y., Sonderegger, I., Lipowsky, G., Jennings, G.T., Schmitz, N., Landi, M., Kopf, M. & Bachmann, M.F., (2010). Combined vaccination against IL-5 and eotaxin blocks eosinophilia in mice. Vaccine, 28 (18): 3192-3200. 16 17Equine metabolic syndrome Alison Morris, BSc(Hons), HND and FHEA Equine Metabolic Syndrome (EMS) is not a disease but a predisposition to weight gain, but obesity is not seen in a collection of risk factors for endocrinopathic laminitis all cases. (laminitis due to an underlying endocrine issue). Ericsson Diagnosis is based upon clinical evaluation, basal et al. (2021) describe it as similar to the human conditions insulin concentrations and response to glucose challenge. of metabolic syndrome and type II diabetes. Therefore Clinical presentation can be similar to that of Pituitary it can be described as a metabolic type. It describes an Pars Intermedia Dysfunction (PPID) (also called insulin resistant phenotype with core symptoms of insulin Cushing’s disease) and the two conditions can occur dysregulation (ID) and increased risk of current or historical simultaneously. The aim of diagnosis is to manage laminitis in horses, ponies and donkeys (Geor et al., 2013). the increased laminitis risk these animals are at and to Laminitis is a primary clinical consequence and more than allow for evidence-based management strategies to be 90% of equines with laminitis have developed it as a result implemented, that will minimise this risk. Management of endocrinopathic disease, Morgan et al. (2015) say this is of afflicted animals is based upon dietary control and if R often as a result of EMS. A consensus statement produced E possible increased exercise. PA in 2019 by the European College Equine Internal Medicine P OBESITY AND EMS D (Durham et al., 2019) states there is little epidemiological EL data defining the prevalence of EMS but that the condition Obesity is defined as excessive adiposity that has a CYC seems more likely in physically inactive animals. Generally, negative impact on health and is currently considered to ER our equine population is less active than it once was, be one of UK’s most serious welfare issues facing equines. %0 concluding it is probable this condition may be increasing Increasing rates of equine obesity are widely reported, with 01 in the population. UK rates reported as 31-54% of the overall population NO Insulin dysregulation can be described as (Furtado et al., 2021), rising to approximately 70% in DE hyperinsulinemia when excessive or prolonged responses native pony breeds (Rendel et al., 2018). Misinterpreted TNI occur to oral or intravenous carbohydrate challenge or workload and feeding regimes plus the increase in equines RP tissue level insulin resistance. Obesity has been linked with being kept purely as companions are factors linked with the condition and EMS affected equines typically exhibit increased obesity and its acceptance. Animals may generalised or regional adiposity (Rendel et al., 2018) or have generalised fat accumulation or regional adiposity. Alison Morris, BSc(Hons), HND and FHEA. Alison achieved her degree in Equine Science from the University of Wales Aberystwyth, having previously completed a Higher National Diploma in Equine Management. Post-graduation she spent four years working in the equine industry in Ireland. In 2002 she took up a lecturing position at the College of Agriculture Food and Rural Enterprise (CAFRE) at their campus in Enniskillen in Northern Ireland where she continues to educate students at Foundation and Honours degree level. Her main teaching focus and passion is equine nutrition, particularly equine weight management and geriatric nutrition. Alison has recently returned to education and is currently completing a MSc in Animal Nutrition at the University of Glasgow. 16 17Animals with EMS often have a predisposition to excessive (Furtado et al., 2018). adiposity or are challenging to achieve weight loss in. EXERCISE IN MANAGEMENT Fitzgerald et al. (2019) suggest that regional adiposity is Using exercise to increase the calories being used each a stronger indicator of EMS than generalised adiposity. day is advantageous for weight loss. Previously laminitic Adiposity should be evaluated through body weight (BW) horses should be sound, have lamellar stability and be determination, fat scoring and cresty neck scores. given veterinary approval to begin an exercise programme. MANAGEMENT OF EMS Alongside the weight loss benefits, exercise also improves We need to address the lifestyles of diagnosed horses, insulin sensitivity and even low intensity work of 5 with increased physical activity, weight loss (if obese) and minutes trotting per day was seen to normalise some blood dietary management frequently being required. Weight loss parameters in previously laminitic ponies (Menzies-Gow in theory is easy to achieve; if the amount of calories being et al., 2014). If horses are able to have increased exercise used each day is greater than the calories being ingested then programmes this can be a beneficial element to their weight loss should occur. Furtado et al. (2021) concluded management. To improve short term baseline insulin levels that UK leisure horse owners were unable to assess the ideal moderate intensity exercise is recommended. Durham et al. body condition and that they felt unable to identify when (2015) suggest that previously laminitic animals who are their own horse was overweight. They also stated that they now sound and with stable hoof lamellae should undertake found excess condition difficult to differentiate from the low intensity exercise (Heart rate 110-150 bpm) for 30 shape they thought their horse ‘was meant to be’. Owners minutes or more at least three times per week. For non- felt that weight management was difficult due to complex laminitic horses with ID they suggest moderate intensity changes required in the management of their animals and exercise (Heart rate 130-170 bpm) for 30 minutes or more described it as being a ‘battle or war’ and that they perceived at least five times per week. it had a negative impact on welfare. Professionals utilising BODY WEIGHT MANAGEMENT collaborative approaches with owners when attempting to address weight loss in horses were more effective In overweight or obese animals, the aim is weight loss Table 1. Approximate horse and pony weight guide (in kg) Height (in hands) Lightweight horse Middleweight horse Heavyweight horse Pony Cob (Thoroughbred) (Sport horse) (Draughts) 10 170-200 11 200-240 12 230 12.2 260 13 250-340 13.2 280-380 14 320-380 360-450 14.2 350-400 380-480 15 470-530 400-470 450-500 15.2 500-580 440-500 470-520 16 480-560 560-630 630-680 16.2 520-590 590-650 650-720 18 19Score Description 0 No visual appearance of a crest (tissue apparent above the ligamentum nuchae). No palpable crest. 1 No visual appearance of a crest, but slight filling felt with palpation. 2 Noticable appearance of a crest, but fat deposited fairly evenly from poll to withers. Crest easily cupped in one hand and bent from side to side. 3 Crest enlarged and thickened so fat is deposited more heavily in the middle of the neck than toward poll and withers, giving a mounded appearance. Crest fills cupped hand and begins losing side to side flexibility. 4 Crest grossly enlarged and thickened, and can R no longer be cupped in one hand or easily bent EP from side to side. Crest may have wrinkles/ AP creases perpendicular to topline. DEL 5 Crest is so large it permanently droops to CY one side. CER % Figure 1. Cresty neck score in horses and ponies Source: (Carter et al., 2008) 001 Reprinted from The Veterinary Journal, 179/2. Rebecca A. Carter, Raymond J. Geor, W. Burton Staniar, Tania A.Cubitt, Pat A. Harris. Apparent adiposity N assessed by standardised scoring systems and morphometric measurements in horses and ponies, 204-210., Copyright (2009), with permission from O Elsevier. DET of between 0.55–1% BW/week until an ideal body weight insulin dysregulated than those with a score below three. NIR As Furtado et al. (2018) determined that owners is achieved. However most animals will require continuous P considered weight loss as a negative experience body weight management after this. Regular body weight and something that would compromise the animal’s and body condition recording is recommended. Ideal body welfare, a reframing of owner perception may be weights are individual to each animal, however the Blue required. Pickering & Hockenhull (2020) concluded that Cross suggest approximate weights for horses on the basis horse owners tend to consult other people rather than of their height and type as outlined in table 1. If possible, professional organisations and that equine veterinarians weighbridges should be used to determine current body are an important source of information. Owners weight, however if this is not available an equine weigh were also found to like practical information on the tape is also suitable. implementation of welfare improvements. The use of fat scoring or body condition scoring procedures can be extremely useful and while these DIETARY MANAGEMENT are subjective, they can be used to assess excess fat and Factors associated with the feeding and nutrition of changes in fat level. Cresty neck scores (Figure 1) have the horse are often associated with divergence from the been suggested as more predictive than body condition animals natural feeding patterns and food types. Horses scores of insulin dysregulation in ponies (Fitzgerald have evolved as trickle feeders who are reported to graze et al., 2019). This study concluded that ponies with a cresty and browse for between 14–20 hours per day. They ideally neck score of 3 or more were five times more likely to be require high fibre diets eaten almost continuously, which 18 19that has been shown to exacerbate hyperinsulinemia in ponies. Durham et al. (2019) suggest that during the first 6-12 weeks of dietary adaptations in ID positive horses, pasture should be fully removed from the diet. Work by Ince et al. (2011) indicated that reducing grazing time is ineffective in ponies as they appear to alter intake to compensate for this. Longland et al. (2011) displayed that grazing muzzles decrease intake and therefore may be a useful tool to allow horses with ID that is under control, to have some grazing. See Managing our horse’s grass intake for further information. Figure 2. Horse with a cresty neck score of 4 on a scale of 0-5. Most horses when given ad-libitum access to forage are seen to eat between 2-2.5% BW DMI per day (NRC, may be at odds with restricted diets. Domestication and 2007). Starvation style diets are not recommended and current management practices often involve diets with can lead to the development of hyperlipidaemia and reduced fibre intake, highly nutritious fibre sources, and other health problems while also causing welfare issues. inclusion of concentrated feeds, all resulting in altered time Minimum forage intake of 1.5% BW DMI per day is budgets and possible weight gain. Providing a lower calorie, recommended to reduce dry matter intake. Overweight / more fibrous diet is recommended to encourage weight obese animals should receive 1.5% BW DMI per day but loss, with such dietary changes being made gradually over of a lower energy content forage, ideally over four meals, a period of ideally 14-21 days to allow the digestive tract although this may not be practical for some owners. Straw time to adapt to new feeds. may be very gradually introduced and included at up to All EMS diagnosed equines require dietary management. approximately 0.25% BW per day to reduce overall energy However all changes must occur with the animals overall intake, intakes higher than this may predispose the horse welfare at the heart of the diet and the diet should not to equine gastric ulcers (Sykes et al., 2015). Hay may be induce other health issues eg hyperlipidaemia or gastric soaked to reduce NSC content. Hay soaked for 7-16 hours ulcers. Careful management is required to allow horses to at ambient temperatures saw sugar and fructan levels meet their physical and physiological requirements to chew (water soluble carbohydrates – WSC) decrease between for extended periods. 24-43% (Durham et al., 2019) and was associated with For obese animals the aim is twofold increased body mass losses in comparison to dry hay. 1. To achieve weight loss and a normal BW and to Steaming this soaked hay would be ideal to reduce any make dietary changes that reduce the risk of future increases in microbial growth that have likely occurred. If weight gain ambient temperatures are increased or water temperature is tepid/warm, then soaking time should be reduced to 1-2 2. Reducing the intake of non-structural carbohydrates hours (Durham et al., 2019). If animals remain weight loss (NSC’s) resistant at these intake levels then intake can be reduced Reducing NSC intake is also required in non-obese to 1% BW DMI. Animals at this reduced intake should be EMS equines, to limit the postprandial (after eating) insulin monitored by a veterinary surgeon to manage the risk of response. Recommendations for both groups therefore other problems such as colic or gastric ulcers. If animals include - exclusion of grains from the diet, feeding forage appear to be weight loss resistant evaluate other potential with less than 10% NSC, soaking of forage for 7-16 hours food sources such as bedding, as Curtis et al. (2011) found in cool conditions, and exclusion of treats with high NSC that horses undergoing dietary restriction were calculated (Durham et al., 2019). to eat more than 3kg/day of wood shavings. If digestible Grass turnout is normally linked to high dry matter energy requirement has been calculated then intake at 64- intakes (DMI) and many pastures have high NSC levels 94% of DE maintenance requirements can be fed (Durham 20 21ID should occur in line with veterinary recommendation. et al., 2019). When intake restrictions are in place attempts should be made to extend eating time as periods of more SUMMARY than four hours without access to forage are linked with Equine Metabolic Syndrome is a collection of risk increased risk of gastric ulcers (Sykes et al., 2015). Horses factors for endocrinopathic laminitis and can be considered on restricted diets and those receiving soaked forages must a metabolic type. Core symptoms include ID, and current receive a vitamin and mineral supplement to allow for or historical laminitis. Obesity is linked with the condition deficiencies that are likely occurring. and EMS affected equines typically exhibit generalised In some cases the veterinary surgeon may recommend or regionally adiposity or a predisposition to weight gain. the use of pharmacologic aids to assist with the effects of However, obesity is not seen in all cases. the diet and exercise adaptions in place. When attempting Management of EMS should include exercise, and body to manage ID, a drug Metformin hydrochloride can be used weight and dietary management. Exercise in sound animals to manage postprandial blood glucose and insulin levels. can assist in reducing body weight and improving insulin Levothyroxine may be prescribed to increase weight sensitivity. Animals should be maintained at an ideal body loss alongside the dietary and exercise adaptions. These weight and fat/condition score. Cresty neck scores of below and other options are available and a detailed discussion three are ideal. Weight loss should be no more than 1% BW regarding the use of any medications should occur with the per week and intake levels should be 1.5% BW DM per day R veterinarian responsible for the horse’s care. It is possible E for weight loss. In weight loss resistant animals this can PA for horses to have PPID and EMS concurrently and these decrease to 1% BW DM per day but only under veterinary P D horses will likely be treated with Pergolide to minimise the supervision. Horses should be removed from pasture until EL effects the PPID will have on ID (Durham et al., 2019). C ID is under control and BW is considered ideal. Forage YC A key element of EMS for the horse owner or caregiver should have an NSC level of less than 10% and soaking ER is continued monitoring of the animal. Body weight, fat/ may be beneficial to achieve this. Inclusion of a suitable %00 ondition scoring and cresty neck scores should continue vitamin and mineral supplement will ensure adequate 1 N even after ideal bodyweight is achieved. Reassessing levels are provided. Continued monitoring of the horse is O responses to oral carbohydrate challenge tests to monitor required to maintain ID and body mass at suitable levels. DETNI REFERENCES RP Blue Cross (Unknown) Fat Horse Slim – A practical guide for managing weight loss in horses. Available at: https://www.bluecross.org.uk/sites/default/files/d8/2020-05/Fat%20horse%20slim.pdf Accessed: (18/02/2020) Carter, R.A., Geor, R.J., Staniar, W.B., Cubitt, T.A. & Harris, P.A. (2009) Apparent Adiposity Assessed by Standardised Scoring Systems and Morphometric Measurements in Horses and Ponies. The Veterinary Journal. 179(2): 204-210 Curtis, G.C., Barfoot,C.F., Dugdale, A.H.A., Harris, P.A & Argo, C. (2011) Voluntary Ingestion of Wood Shavings by Obese horses Under Dietary Restriction. British Journal of Nutrition, 106(S1): S178 - S182 Durham, A,E., Frank, N., McGowan, C.M., Menzies-Gow, N.J., Roelfsema, E., Vervuert, I., Feige, K. & Fey, K. (2019) ECEIM Consensus Statement on Equine Metabolic Syndrome. Journal of Veterinary Internal Medicine, 33: 335-349 Ericsson, A.C., Jonson, P.J., Gieche, L.M., Zobrist, C., Bucy, K., Townsend, K.S., Martin, L.M., & LaCarrubba, A.M. (2021) The Influence of Diet Change and Oral Metformin on Blood Glucose Regulation and the Fecal Microbiota of Healthy Horses. Animals, 11(4): 976. Fitzgerald, D.M., Anderson, S.T., Sillence, M.N & DeLat, M.A. (2019) The Cresty Neck Score is an Independent predictor of Insulin Dysregulation in ponies. PlosOne. 14(7): e0220203 Furtado, T., Perkins, E., Pinchbeck, G., McGowan, C., Watkins, F & Christley, R. (2021) Exploring Horse Owners’ Understanding of Obese Body Condition and Weight Management in UK leisure horses. Equine Veterinary Journal, 53: 752-762. Furtado, T., McGowan, C., Perkins, E., Pinchbeck, G., Watkins, F & Christley, R. (2018) Lost in Translation: Examining Communication between Horse-Owners and Professionals about Equine Weight Management. Equine Veterinary Journal, 50(Suppl 52): 11 Geor, R.J., Harris, P.A. & Coenen, M. (2013) Equine Applied and Clinical Nutrition, Health, Welfare and Performance. London : Saunders Elsevier. Ince, J., Longland, A.C., Newbold, J.C. & Harris, P.A.(2011) Changes in Proportions of Dry Matter Intakes by Ponies with Access to Pasture and Haylage for 3 and 20 hours per day Respectively for six weeks. Journal of Equine Veterinary Science, 31(5-6): 283 Longland, A.C., Barfoot, C., & Harris, P.A. (2011) The Effect of Wearing a Grazing Muzzle v’s not Wearing a Grazing Muzzle on Pasture Dry Matter intake by Ponies. Journal of Equine Veterinary Science, 31(5-6): 282-283 Menzies-Gow, N.J., Wray, H., Bailey, S.R., Harris, P.A., & Elliott, J. (2014) The Effect of Exercise on Plasma Concentrations of Inflammatory Markers in Normal and Previously Laminitic Ponies. Equine Veterinary Journal, 46(3): 317-321 Morgan, R., Keen, J. and McGowan, C. (2015) ‘Equine Metabolic Syndrome’. Veterinary Record. August. Pp 173-179. National Research Council (USA) (2007) Nutrient Requirements for Horses. 6th edn Washington DC: National Academy of Sciences. Pickering, P., & Hockenhull, J. (2020) Optimising the Efficacy of Equine Welfare Communications: Do Stakeholders Differ in Their Information-Seeking Behaviour and Communication Preferences? Animals, 10(1): 21 Rendel, D., McGregor Argo, C., Bowen, M., Carslake, A., Harris, P., Knowles, E., Menzies-Gow, N., & Morgan, R. (2018) Equine Obesity: Current Perspectives. UK-Vet Equine, 2(5): 1-19 Sykes, B.W., Hewetson, M., Hepburn, R.J., Luthersson, N & Tamzali, Y. (2015) European College of Equine Internal Medicine Consensus Statement – Equine Gastric Ulcer Syndrome in Adult Horses. Journal Veterinary Internal Medicine, 29: 1288-1299 20 21The role of electrolytes in the exercising horse Dr. Femke Schaafstra, PhD Equine Nutrition, MSc, BSc Electrolyte supplements are often thought to be needed and a decreased water intake (Meyer, 1984). An acute only by high-level sport horses, especially those competing Sodium deficiency might result in uncoordinated muscle in endurance events. However, when horses sweat for a contraction and chewing (Meyer, 1984). When a diet has prolonged time electrolyte deficiency can occur. This might a marginal or excessive sodium content, the horse appears result in dehydration, impaired performance, fatigue, and in to regulate the external balance by restricting or increasing severe cases even ‘tying-up’. This article aims to improve urinary excretion (Tasker, 1967; Rose, 1990). In the diet, the understanding of electrolytes and their use in horses. Sodium is normally accompanied by Chloride, which is the Electrolytes are electrically charged minerals and are most common anion (negatively charged molecule) in the vital to many key functions in the body. They are needed for extracellular body fluid. Like Sodium, Chloride is involved basal processes in the body, including conducting nervous in maintaining acid-base balance and osmotic regulation impulses, contracting muscles, regulating hydration and is a component of gastric sections as hydrochloric acid and pH levels (acid-base balance) of body fluids. The and bile. When Sodium is sufficiently present in the diet, a electrolytes of primary importance for the horse include deficiency in Chloride is unlikely to occur. However, when + + - Sodium (Na ), Potassium (K ), Chloride (Cl ), Magnesium horses are supplemented with large amounts of Sodium 2+ 2+ + + (Mg ), and Calcium (Ca ) (Frape, 2010), with Na , K , bicarbonate metabolic alkalosis is induced and might result - and Cl as the principal ions (Groenendyk et al., 1988). in decreased food intake, weight loss, muscle weakness, Sodium, Potassium, and Chloride are major players in the dehydration, constipation, decreased milk secretion, and maintenance of the cellular and extracellular environment. depraved appetite (Tasker, 1980; Fettman et al., 1984; Sodium is the principal cation (positively charged Coenen, 1991). Whereas Sodium and Chloride are found molecule) in the extracellular fluid and is involved in the predominantly in extracellular fluids, Potassium is mainly maintenance of acid-base balance and osmotic regulation retained within cells and, in particular, in muscle tissue of body fluids (NRC, 2007). In the case of chronic Sodium (Meyer, 1987). In addition to maintaining acid-base balance depletion horses have decreased skin turgor, a tendency to and osmotic pressure, Potassium is the most quantitatively lick objects, a slowed rate of eating or even stop eating, 1 Table 1. Amount of electrolytes in constituents of equine diets (g/kg DM) Byproducts Electrolyte Grass, roughage Native grain Protein-rich seeds Milling Oil industry Na <1 <1 K >20 4-8 8-12 10-13 12-20 Cl 4-8 <1-1.5 1-1.5 1-1.5 0.4-1 1Adapted from Coenen (2013). 22 23important cation involved in neuromuscular excitability (Kronfeld, 2001). A diet high in forages generally provides an adequate amount of electrolytes to the horse (Table 1) (Coenen, 2013) and the excessive intake of electrolytes is counteracted in the horse by renal and faecal excretion. When horses are at rest, intake, absorption and faecal and urinary excretion are in a steady state. However, when horses start to exercise, the acid-base balance drops as soon as horses start to sweat (Coenen, 2005). During exercise, horses produce an enormous amount of metabolic heat and core body temperature can easily increase from 37°C at rest to 42°C (McKeefer, 2008). As for humans, the most effective way for horses to eliminate the excess heat produced is through evaporation of fluid from the body surface (sweating) (Figure 1) and the respiratory tract Figure 1. Considerable amounts of electrolytes and water can be RE lost in sweat and should be replaced. (Hodgson et al., 1994; Zeyner et al., 2013). When compared PAP and cations, which would then be available for absorption to human sweat, equine sweat is hypertonic with electrolyte DEL (Kronfeld, 2001). Based on a dry matter intake for concentrations higher than that of plasma. Equine sweat CY intensively exercising horses of 2.2kg/100kg BW/day (2.2% contains per liter approximately 3.1g Na, 1.8g K, and CER BW) a daily intake of approximately 1.3kg/100kg BW of a 6.3g Cl (Meyer, 1995; Flaminio & Rush, 1998; Waller & %0 high-quality roughage is recommended to fulfill electrolyte 0 Lindinger, 2021). Potassium sweat concentration is 10 to 15 1 N requirements (Coenen, 2005). When the gastrointestinal times greater than plasma Potassium concentration, whereas O D tract is not able to compensate for electrolyte losses, the Chloride concentration in horse sweat is twice as high as ET + - , and Cl excretion (Robert kidney may reduce water, Na plasma Chloride concentration. Sodium concentration in NIRP et al., 2010). Furthermore, to maintain sweating losses horse sweat is approximately equal to its concentration in of water and electrolytes, it is also likely that soft tissue, plasma (Flaminio & Rush, 1998). Cutaneous losses, other like skeletal muscle, are important sources of electrolytes than Sodium, Potassium, and Chloride can be neglected as and water. Although the gastrointestinal tract can serve as a factor for the external balance (Meyer, 1995; Flaminio a temporary reservoir, and the horse is able to conserve & Rush, 1998; McCutcheon & Geor, 1998). As sweat is + + - water and ions during prolonged exercise via renal tubular rich in electrolytes with Na , K , and Cl as the predominant conservation, these mechanisms seem to be insufficient ions, prolonged sweating and dehydration are associated to compensate for these losses (NRC, 2007; Robert et al., with significant water and electrolyte depletion in exercised 2010). Significant electrolyte losses via perspiration and horses (Coenen, 2005; Waller & Lindinger, 2021). To subsequent electrolyte imbalances may induce muscle balance these cutaneous losses internally, the horse can fatigue and might even contribute to the development of enforce electrolyte absorption from the gastrointestinal exertional rhabdomyolysis (“tying up”) in some horses tract, reduce renal excretion and release electrolytes from eg. muscle tissue (Coenen, 2005). Intake of roughage could (Harris, 1989; Furman, 2015). Therefore, it is important to enforce the reservoir function of the gastrointestinal tract, estimate the electrolyte losses of horses during training and as fermentation of fibers from roughage releases water competition by estimating the amount of sweat loss. 22 23However, unstandardised methodological practices to movement, individual athletic fitness, transport, climatic determine sweat loss can produce inaccurate results. To adaptation, the character of the subsoil, and the temperament develop a novel sweat scoring system Zeyner et al. (2013) or degree of arousal of the horse (Ecker & Lindinger, 1995; studied the exercise-induced body weight losses in 35 Jansson et al., 1995; McCutcheon & Geor, 1998; Zeyner Warmblood-type horses subjected to a low (LW) and a et al., 2013). medium (MW) intensity exercise regimen under German Not surprisingly, when the environmental temperature conditions. Following each exercise, the horses were and humidity increase the thermal gradient between the visually inspected and 5 distinct ‘sweat’ scores could be skin and environment (skin-ambient vapor pressure) is determined and associated with a defined sweat loss range reduced and cutaneous heat loss is impaired (Hodgson et (Table 2). Based on this technique, a horse performing al., 1994). The horse’s body can even gain heat from the light work (LW) at an ambient temperature of 20°C and environment when the ambient temperature exceeds skin a sweat score of 1 excretes approximately 4L of sweat temperature (greater than 35-36°C) (McCutcheon & Geor, corresponding to 40grams of electrolytes containing 2008). In these circumstances, the cooling effect of sweat + + - 12.4g Na is limited as horses produce more sweat which just runs , 6.4g K and 22g Cl (Meyer, 1995; Zeyner et and drips off their body. In response to this extensive sweat al., 2013). The researchers concluded that this technique loss, large amounts of Sodium and fluids are lost, which permits accurate estimation of exercise-induced sweat results in hypotonic dehydration (Hodgson et al., 1994). losses on an individual basis with higher accuracy than Dehydration of as little as 1.2% of body weight impairs other available methods. However, this technique can be thermoregulation and exercise performance (Hyyppä et affected by several factors, including weather conditions al., 1996). Therefore, oral electrolyte supplementation in (ambient temperature, relative humidity, precipitation), air Table 2. Sweat scores with assigned sweat pattern (observed immediately after exercise without the saddle), their associated sweat and 1 electrolyte loss ranges for practical use 2 Sweat score Sweat pattern Total sweat loss (L) Total electrolyte loss (g) 1 The area under the saddle is partly dry, 1-4 ±10-40 partly dark, sticky, and moist. The throat area is sticky, and the flanks are darker than normal. 2 The area under the saddle and the throat are 4-7 40-70 both wet, there are small white areas at the edges of the saddle corners, and foaming may occur at sites of friction between the throat and reins and between the limbs. 3 There is foam on the back of the bridle 7-9 70-90 and noseband, the flanks are clearly wet, and the area under the saddle and girth are consistently wet. 4 The throat and flanks are completely wet, 9-12 90-120 above the eyes are moist and have dark wrinkles, and there is pronounced foaming between the limbs 5 The horse is actually dripping fluid above 12-18 120-180 the eyes and under the belly. 1Adapted from Zeyner et al. (2013). 24 25combination with water is recommended to restore the GLOSSARY water and electrolyte balance. ACID-BASE BALANCE: the integrated sum of many As already discussed, equine sweat is isotonic or slightly simultaneously acting physiological processes, like hypertonic relative to plasma, containing high concentrations cellular respiration, ventilation at the lungs, renal + + - of Na , K , and Cl and electrolyte supplements should function, hepatic function, and cellular (primarily therefore contain these ions. Additionally, small amounts of skeletal muscle) ion transport, on the physical and 2+ 2+ Ca and Mg are also lost, and because these are important chemical state of body fluids. for cellular function, they should also be replaced (Meyer, EXCITABILITY: the condition of reacting strongly to 1995). Normally, Potassium intake greatly exceeds stimuli (= things that cause a physical reaction). + requirements due to the high K concentrations in most EXTRACELLULAR FLUID: fluid that is found types of roughages (Table 1) and there will be no need for in blood, lymph, body cavities lined with serous Potassium supplementation if the horse has a normal food (moisture-exuding) membrane, in the cavities and intake post-exercise (Jansson et al., 1995; Nyman et al., channels of the brain and spinal cord, and muscular 1996). However, the Sodium content of the horse’s diet and other body tissues. It differs from intracellular is often low and Sodium deficits should be replenished R fluid (fluid within the cells) in that it generally has a EP in exercising horses. It is, therefore, important that they high concentration of sodium and low concentration of AP have free access to common salt (NaCl) to prevent Sodium potassium, while intracellular fluid is high in potassium DEL depletion. However, providing horses with a salt block and low in sodium. CYC would not be of any benefit. According to Jansson et al. E HYPERTONIC: having a higher osmotic pressure than R (1996), voluntary salt intake of exercising horses was not % body fluid (extracellular fluid) or intracellular fluid. 00 increased when they were offered salt blocks. This might be 1 HYPOTONIC: having a lower osmotic pressure than N since a salt block is a concentrated salt solution, which may O body fluid (extracellular fluid) or intracellular fluid. D cause taste aversion and/or a temporary inhibition of the ET ISOTONIC: having the same osmotic pressure as body N Sodium appetite (Jansson et al., 1996). So, additional NaCl IR fluid (extracellular fluid) or intracellular fluid. P intake could therefore be improved in the form of a salty, NEUROMUSCULAR: relating to the nerves that high palatable feed or adding table salt to your horse’s daily control muscles. ration on exercise days (Coenen et al., 1995). As Sodium is absorbed from the intestinal lumen by diffusion through OSMOSIS: a process by which molecules of a solvent waterfilled channels, cotransport with organic solutes (eg. tend to pass through a semipermeable membrane - from a less concentrated solution into a more glucose and amino acids), cotransport with Cl and the + + concentrated one. countertransport of Na in exchange for H , Sodium uptake could be increased by the addition of glucose and glycine to efficient restoration of fluid loss and electrolyte imbalances the electrolyte solution (Wright & Loo, 2006). However, the in exercise-like dehydrated horses could be achieved by addition of glucose in an isotonic electrolyte solution might providing the horse with an isotonic electrolyte solution fail to adequately replenish electrolyte losses and impair similar to equine sweat (Monreal et al. , 1999). the rehydration process. To be isotonic, fluids containing Trainers/riders apply different methods to avoid glucose have fewer electrolytes, and subsequently dehydration and decrease horse performance capacity. decreased amounts of electrolytes could be absorbed (Sosa In general, procedures to stimulate water intake through León et al., 1995; Monreal et al., 1999). Hence, rapid and 24 25electrolyte consumption to compensate for fluid and excretion of water with additional electrolytes (Lindinger electrolyte losses are used. Supplementation during or after & Ecker, 2012). Thus, providing only water would not be exercise as well as preloading is practiced, but there is still as successful in rehydrating the horse as the administration no specific procedure recommended. During endurance of a glucose-electrolyte solution (Hyyppä et al., 1996). As training or rides, fluid losses appear to be balanced by Sodium and fluid loss after exercise result in hypotonic water intake and as renal absorption seems insufficient to dehydration, an insufficient osmotic stimulus may lead + - compensate for Na and Cl , supplementation of these ions to a lack of desire to drink (Flaminio & Rush, 1998). could be of benefit (Robert et al., 2010). Carlson (1985) Therefore, providing the horse salt in their feed and free suggested an easy and cheap recipe for an electrolyte excess to water would be recommended (Jansson et al., solution very similar to 1L of equine sweat containing one 1996). Preloading a large volume of electrolytes is another level tablespoon (17grams) of Sodium chloride (common strategy that could be applied. Waller & Lindinger (2021) salt) and one level tablespoon of Lite Salt (Sodium and studied the effect of supplementation of water (1L) or Potassium chloride) dissolved in 4L of water. However, electrolytes dissolved in 1L or 3L water before exercise horses might refuse the saline solution due to taste aversion on horses' performance, plasma, and sweating response. and should be trained to drink during competition. In the They concluded that provision of a hypotonic electrolyte case of post-exercise replacement, providing concentrated supplement 1h before exercise provides a source of water electrolytes may have a detrimental effect as water and ions that potentially support muscle and whole-body absorption may be impaired during recovery (Chapman, ion balance during periods of prolonged sweat ion losses 2011). Because when horses ingest concentrated (Waller & Lindinger, 2021). electrolyte solutions (slurries and pastes) a net flux of SUMMARY water from the extracellular fluid compartment into the upper gastrointestinal tract is caused. So, water is moving Electrolytes play an important role in hydration and in the wrong direction and induces further dehydration of cellular function in horses. Horses at rest are perfectly the horse. In contrast, the provision of water alone results able to fulfill their electrolyte requirements by a high- quality forage-rich diet. However, during prolonged or in a dilution of the extracellular fluid and results in renal Dr Femke Schaafstra, PhD, MSc, BSc. Femke is a Senior lecturer in Animal Nutrition at HAS University of Applied Sciences (‘s-Hertogenbosch, The Netherlands). Femke studied BSc Animal Husbandry at the International Agricultural College Larenstein in Deventer, with a specialisation in Equine Management. When this study was successfully completed, she started with the MSc Animal Science at Wageningen University in Wageningen, with a specialisation in Animal Nutrition. After graduation, she worked for a pet food manufacturer as part of the nutrition team before moving on to work for HAS University of Applied Sciences. During her work as a Senior lecturer, Femke completed a Ph.D. in equine nutrition, where she studied the use of TiO 2 as a digestibility marker in equine at the Faculty of Veterinary Medicine at Utrecht University. Femke has a passion for helping others to learn and understand the importance of nutrition and its role in animal welfare. 26 27high-intensity exercise horses lose large quantities of oral isotonic electrolyte supplementation similar to equine sweat is recommended. Providing salt topped on feed electrolytes and fluid by sweating. To determine the amount and free access to water or iso- or hypotonic solutions of electrolytes lost, sweat rate could be scored with help of before ingestion of dry feeds at least 1h prior to training a novel sweat scoring technique. Replenish of electrolytes or competition benefits muscle function and exercise performance during periods of prolonged sweating. and rehydration of the exercising horse is important and REFERENCES Carlson, G.P. (1985). Medical problems associated with protracted heat and work stress in horses. The Compendium on Continuing Education for Practicing Veterinarians, 7:542-550. Chapman, B. (2011). Comparison of the efficacy of preloading versus reloading electrolyte supplementation in novice competition horses. Dissertation BSc (Hons), Moulton College. Coenen, M. (1991). Chlorine metabolism in working horses and the improvement of chlorine supply. Proceedings of the Equine Nutrition and Physiology Symposium 12, p. 91. Coenen, M., Meyer, H. & Steinbrenner, B. (1995). Effects of NaCl supplementation before exercise on metabolism of water and electrolytes. Equine Veterinary Journal, 18:270-273. Coenen, M. (2005). Exercise and stress; impact on adaptive processes involving water and electrolytes. Livestock Production Science, 92:131-145. Coenen, M. (2013). Macro and trace element in equine nutrition. In: Geor, R.J., Harris, P.A. & Coenen, M. (eds) Equine Applied and Clinical Nutrition. Health, Welfare and Performance. London, Elsevier Saunders, p. 190-228. Flaminio M.J.B.F. & Rush, B.R. (1998). Fluid and electrolyte balance in endurance horses. Veterinary Clinics of North America: Equine Practice, 14:147-158. Fettman, M.J., Chase L.E., Bentinck-Smith, J., Coppocdk C.E. & Zinn, S.A. (1984). Effects of dietary chloride restriction in lactating dairy cows. Journal of the American R Veterinary Medical Association, 185:167-172. EP Frape, D. (2010). Feeding for performance and the metabolism of nutrients during exercise. In: Frape, D. (ed) Equine Nutrition and Feeding. Wiley-Blackwell, p. 222-264. AP Furman, J. (2015). When exercise causes exertional rhabdomyolysis. 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Animal Physiology and Animal Nutrition (Berl.), 9:246-250. 26 27Nutrition of the stallion Anouk Frieling, MSc Equine Sciences, BSc (Hons) Horses are seasonal breeders and the breeding season BODY CONDITION SCORE for horses in the northern hemisphere generally lasts It is important for an active breeding stallion to maintain from April to October (Davies Morel, 2015), although for a healthy body weight and body condition throughout the Thoroughbred stallions this can be as early as February. breeding season as it has been shown that an increased Semen collection for artificial insemination (AI) at most body condition in bulls has negative effects on sperm studs starts early on in the year, before the start of the quality and quantity, with sperm motility after collection breeding season, and is carried out throughout the breeding from heavier bulls being lower, meaning the sperm were season (Janett et al., 2003; Aurich, 2016). To perform less active (Beran et al., 2011). Research suggests that well as a breeding stallion, whether that be for natural the body condition of the pregnant mare has an influence covering or AI, it is important that the diet of the stallion on the pregnancy and the foal (Morley & Murray, 2014). meets their daily requirements to maintain body condition Currently there is limited research available about the effect and overall health (Hiney, 2018) (Figure 1). The nutrient of body condition of the stallion on fertility (Geor et al., requirements for a stallion are similar to those of an adult 2013), but optimal body condition is known to support horse, except when actively covering when it is suggested the general health of the horse (Thatcher et al., 2008). that the nutrient requirements increase about 25% (Gibbs & The body condition of a horse can be scored using body Pas, 2011). Like all horses though, requirements can differ condition scoring (BCS) or fat scoring. It is suggested that between breeding stallions depending on their age, general a BCS between 5 and 6 is ideal for a stallion during the health, behaviour, breeding frequency during the breeding breeding season, using the 9 point BCS system developed season and if the stallion is also an active competition horse by Henneke et al. (1983) (Table 1) (Geor et al., 2013). (Geor et al., 2013). The equivalent would be a score of 3 on a scale of 0 to 5. Assessment of fat stores is a helpful tool to manage the energy intake of the horse and will help to avoid over or underfeeding of the stallion (Houssou et al., 2020). ENERGY AND PROTEIN REQUIREMENTS Stallions that do not compete require energy for maintenance during the non–breeding season (Harris, 1997), whilst during the breeding season the stallion requires energy for maintenance plus additional energy for reproductive activities (Ellis, 2013). Dietary energy is an essential component in the diet to maintain the stallion’s body condition which, as mentioned earlier, is essential for the general health of the stallion (Potter & Gibbs, 2011). The energy requirements of the breeding stallion during the breeding season depend on the breeding frequency and are Figure 1. Stallions are seasonal breeders and therefore the breed- ing season generally lasts from April to October. Due to increased similar to the requirements of a horse performing exercise activity the diet should meet the stallion’s requirements during the (Mantovani & Bailoni, 2011; Martin-rosset, 2015). Inactive breeding season. 28 29Table 1. The 9-point Body Condition Score system developed by Henneke et al. (1983) which can be used to score the condition of the body of the horse and is a useful tool for managing the diet and overall health of the horse. Stallions during the breeding season should score between 5 and 6 which is between moderate and moderately fleshy and should avoid higher or lower scores which indicate obesity or underfeeding in horses. Score Description 1: Poor • No fat tissue can be felt on the horse • Bone structure, ribs and pelvis can be easily seen • Ribs can be easily felt • Horse looks extremely skinny 2: Very thin • The horse is slightly covered in some fat tissue • Bone structure, ribs and pelvis can be seen • Ribs can be felt • Horse looks skinny 3: Thin • There is visible fat build up about halfway up the spine of the horse • Bone structure, withers, ribs and pelvis are slightly covered in fat • Ribs can be felt 4: Moderately thin • Horse is not obviously thin R • A layer of fat can be felt on the horse’s bone structure EP • Ribs are faintly visible and can be felt AP 5: Moderate • The ribs are not visible but can be felt DEL • The neck and the shoulders blend into the body of the horse CY • Withers are rounded CER 6: Moderately fleshy • Fatty tissue is increasing over the ribs, withers and along the sides of the neck %0 7: Fleshy • Ribs can be felt but fat can be felt between the ribs 01 • Fat is deposited along the neck and withers NO 8: Fat • Difficult to feel the ribs DE • The area around the withers, shoulders and neck is filled with fat TN • Thickening of the neck IRP • Increase of fat deposit along the inner thighs 9: Extremely fat • Increase of patchy fat on the body of the horse • Ribs cannot be felt breeding stallions (stallions performing a covering every 2 (Potter & Gibbs, 2011). Non-structural carbohydrates, such days) have similar energy requirements to those of horses as starch, are transformed into quickly accessible energy in light work, whilst active breeding stallions (stallions for immediate use or are stored in the form of glycogen performing two or more coverings per day) require an in the horse’s muscle tissue when starch supply exceeds energy intake comparable to horses performing moderate immediate energy demands. The stored glycogen is useful exercise (Geor et al., 2013; Martin-rosset, 2015). Energy to the horse as it can provide energy when blood glucose is mainly derived from structural carbohydrates (fibre), levels decrease (Potter & Gibbs, 2011). About 60 to 70% non–structural carbohydrates (starch and sugar) and of the daily energy intake from the stallion’s diet is derived fats in the diet (Duren, 1955). When protein is overfed from the fermentation of structural carbohydrates (fibre) the excess protein can be used as an energy source by into the volatile fatty acids acetate, butyrate and propionate the horse but this is not one of the main energy sources (Argenzio et al., 1974; Bergman, 1990). Therefore, it is (Johnson & Duberstein, 2010). Fat is a slowly released important to include high fibre feedstuffs, such as hay, energy source and therefore provides long-term energy in the stallion’s diet. Providing a high fibre diet is also 28 29essential for a healthy hindgut microbiome composition 2011). It is important that daily protein requirements are which aids efficient digestion of nutrients (Grimm et al., not exceeded because excess protein will be excreted in 2017). It is also important that the stallion consumes at least the form of ammonia instead of being absorbed by the 2.0% of their bodyweight in dry matter (NRC, 2007). This body which is inefficient use of dietary protein (Johnson is equal to at least 10 kilograms of dry matter for a 500kg & Duberstein, 2010). In table 2 the energy and protein horse (NRC, 2007). To meet the energy requirements of the requirements for the adult breeding stallion are shown stallion, especially for very active breeding stallions who based on the breeding frequency of the stallion. require more energy for their performance, energy dense MINERALS AND VITAMINS cereal grains or oils can be added to the diet (Harris, 1997). Vitamins and minerals are only required in small amounts A fibre-based diet supplemented with oils/concentrates in the diet in comparison to other nutrients, however supplies the stallion with long-term and short-term energy, they have many important functions in the body such as helping to maintain ideal body condition and supporting supporting healthy tissue and bone development (Raub, gastrointestinal and mental health throughout the breeding 2010). Therefore it is important that the diet fed meets the season (see Your horse’s gut: gastrointestinal structure vitamin and mineral requirements of the stallion (NRC, and function). 2007). Minerals can be divided into macro minerals and The digestion of dietary protein provides the body trace minerals. Macro minerals (Calcium [Ca], Phosphorus with amino acids which are essential for the production [P], Magnesium [Mg], Potassium [K], Sodium [Na] and of proteins which have different functions in the body of Chloride [Cl]) are required in grams per day whilst trace the horse (Johnson & Duberstein, 2010). The mature horse minerals (Iron [Fe], Copper [Cu], Zinc [Zn], Manganese normally does not require high levels of protein in their [Mn], Cobalt [Co], Selenium [Se] and Iodine [I]) are diet (Johnson & Duberstein, 2010), with recommendations required in milligrams per day (Geor, 2008). Similarly, stating that approximately 10% of the diet should consist vitamins can be divided in fat-soluble (Vitamins A, D, E of protein to meet the maintenance requirements of an and K) and water soluble (Vitamins B and C), with fat- adult horse (Potter & Gibbs, 2011). In contrast, the protein soluble vitamins able to be stored in the body whilst excess requirements for a stallion during the breeding season B vitamins and Vitamin C are excreted from the body via changes slightly due to increased activity (Graham-Thiers the urine. Horses mainly derive minerals and vitamins from et al., 2001). Level of activity has an effect on the retention the forages and concentrates comprising their daily diet of nitrogen. Stallions that sweat due to increased activity (Potter & Gibbs, 2011). Vitamin and mineral supplements have greater nitrogen losses, leading to a slight increase in also offer an option for providing such nutrients and can be dietary protein requirement to compensate for these losses particularly useful for stallions who have a tendency to gain (Miller-Graber et al., 1991; Lawrence, 2008). Protein is weight easily as supplements are generally low energy. also important for growth and therefore the young growing Under and overfeeding of minerals and vitamins due stallion will need extra protein in addition to the protein to an unbalanced diet can cause various health issues and required for maintenance and activity (Potter & Gibbs, should therefore be avoided by creating a tailored diet Table 2. Energy and protein requirements of a 600 kg breeding stallion depending on breeding frequency (NRC, 2007; Geor et that will suit the nutritional needs of the stallion (Lewis, al., 2013). 1982; Geor, 2008). For example, a Vitamin E deficiency Breeding can result in decreased sperm motility and an increase of Nutrients Non-breeding Breeding actively abnormal spermatozoa in stallions (Bazzano et al., 2021). Digestible 76.1 100.4 117.2 Similar to energy and protein requirements, mineral and Energy (Mj/day) vitamin requirements of the stallion increase slightly Crude Protein 648 839 921 during the breeding season due to their increased activity. (g/day) Table 3 displays the mineral and vitamin requirements for 30 31Table 3. The daily mineral, trace mineral and vitamin requirements but also for body cells that require water to function for non-breeding, breeding and breeding actively 600 kg breeding (Geor et al., 2013). stallions according to NRC (2007). Breeding NUTRIENT SUPPLEMENTATION FOR FERTILITY Nutrients Non-breeding Breeding actively Semen quality and quantity of natural covering stallions Minerals (g/day) should be as optimal as possible as natural covering stallions Ca 24.0 36.0 42.0 can only cover a certain number of mares per breeding P 16.8 21.6 25.2 season. Optimal quality and quantity results in higher Mg 9.0 11.4 13.8 K 30.0 34.2 38.4 pregnancy rates in mares which increases reproductive Na 12.0 16.7 21.3 performance (Contri et al., 2011). Quantity and quality Cl 48.0 56.0 63.9 of semen used through AI should also be optimal to be Trace minerals (mg/day) able to cool and freeze the semen for storage and travel Fe 480.0 480.0 540.0 (Bazzano et al., 2021). Techniques have been developed to Cu 120.0 120.0 135.0 be able to successfully store semen and inseminate mares Zn 480.0 480.0 540.0 (Alvarenga et al., 2016). Even though cooling and freezing Mn 480.0 480.0 540.0 of the semen improves reproductive efficiency, the process RE Co 0.6 0.6 0.7 P of cryopreservation can also cause oxidative damage A Se 1.2 1.2 1.4 P (Aurich, 2005; Peña et al., 2019). Such damage reduces D I 4.2 4.2 4.7 EL sperm motility and fertility which has a negative effect on C Vitamins (IU/day) YC pregnancy rates of inseminated mares (Peña et al., 2019). A Vitamin A 18000 27000 27000 ER such, there is an interest in developing methods to decrease Vitamin D 3960 3960 3960 %00 semen susceptibility to cold shock (Goedde, 2016). One Vitamin E 600 960 1080 1 N of the methods which has been studied to improve stallion O D fertility is supplementation of different nutrients to optimise E the adult stallion according to the NRC (2007) based on T metabolic pathways in the body of the stallion (Freitas et NI breeding activity. R al., 2016; Bazzano et al., 2021). Polyunsaturated fatty acids P WATER REQUIREMENT (PUFAs) are nutrients found in the lipid composition of the semen of the stallion (Wolkmer et al., 2019). One of these An adult horse requires approximately 4 to 6 litres of PUFAs is docosahexaenoic acid (DHA) (Wolkmer et al., water per 100 kg of body weight (NRC, 2007; Geor, 2008), 2019). Brinsko et al. (2005) supplemented the feed of eight although requirements can increase due to environmental fertile stallions with DHA for 14 weeks during a crossover temperature and activity (Frape, 2007). Depending on trial. The DHA levels in semen of the supplemented the intensity and duration of activity, the horse’s water stallions increased by 50%. Results showed that after requirements can increase at least 20% as result of water cooling the sperm for 48 hours the total and progressive lost in sweat (Frape, 2007; Geor et al., 2013). Requirements motility of the sperm increased (Brinsko et al., 2005). can also vary between different housing situations. Stallions Total motility is the overall percentage of moving sperm, that are mainly kept in the stable or are turned out in a sand whilst progressive motility is the percentage of sperm that paddock will require more water in comparison to stallions somewhat moves in a straight line. The supplementation of that have access to fresh forages such as grass which DHA increased the motility of sperm from stallions which contains approximately 80% water (Geor et al., 2013). had a sperm motility of less than 40% after 24 hours of Providing enough water is essential for digestive purposes cooling, prior to supplementation (Brinsko et al., 2005). 30 31Therefore it is suggested that supplementing stallions with DHA has a positive effect on the motion characteristics of semen, which is beneficial for natural covering stallions, and will increase freezability of semen which is beneficial for AI (Brinsko et al., 2005). For more in depth information about PUFAs, DHA and the effect of DHA on reproductive processes, please refer to Nutrient spotlight: essential fatty acids. Besides DHA, the effects of pomegranate seed oil on stallion fertility has been studied. In a study carried out by Nouri et al. (2018) 200ml of pomegranate seed oil was supplemented to eight Arabian stallions for a period of 90 days. The results showed no significant effects on fresh collected semen but did show a positive effect on cooled Figure 2. Supplementing the stallions feed with nutrients such as semen, where the pomegranate supplementation increased DHA and vitamin E has been shown to have positive effects on their fertility. integrity and viability of semen (Nouri et al., 2018). Total motility of post-thawed sperm was also increased the antioxidant improved the total and progressive motility in stallions supplemented with pomegranate seed oil of sperm which had been cooled for 48 hours and had been (Nouri et al., 2018). warmed up afterwards for 10-30 minutes (Gee et al., 2008). The compound L-carnitine has been found in the Goedde (2016) evaluated the effect of supplementing a composition of epididymal secretions of the stallion. combination of DHA derived from micro-algae, Vitamin E Therefore, it is suggested that L-carnitine is able to function and Selenium to stallions. Results of this study suggest that the combination of these nutrients improves the motility of as a marker for semen quality in the stallion (Stradaioli et fresh and also cooled sperm after 60 day supplementation al., 2000). Stradaioli et al. (2004) supplemented 20mg of (Goedde, 2016; Wood et al., 2017), with this benefit being L-carnitine to eight low (progressive motility <50%) and considerable for sperm collected from stallions with a high motility (progressive motility >50%) stallions for progressive motility of less than 40% which were classified 60 days which resulted in a higher sperm concentration as ‘poor coolers’ as the supplement considerably increased and progressive motility in low fertility horses. Therefore total and progressive motility of stallion sperm (Goedde, L-carnitine can have a positive effect on sperm motility of 2016). For more in-depth information about Vitamin E stallions producing low motility sperm, making L-carnitine please refer to Nutrient spotlight: vitamin E. beneficial for sperm production of natural covering stallions The results of studies mentioned above show that the and stallions used for AI. The L-carnitine supplementation supplementation of certain nutrients can enhance fertility did not affect semen of the high motility stallions of stallions through improved sperm motility and ability to (Stradaioli et al., 2004). cool and freeze sperm, and by limiting oxidative damage Research has also focussed on the effects of antioxidant after using these storage techniques. Such benefits may supplementation on stallion fertility. One of the also apply to natural covering stallions as the greater sperm antioxidants that has been studied is Vitamin E. Gee et al. motility will increase their fertility which has the potential (2008) supplemented 3000IU of vitamin E per day to 15 to translate to increased pregnancy rates. Limiting oxidative stallions for 14 weeks and found that supplementation of stress after sperm storage for AI increases the insemination 32 33success rate in mares with the potential to result in higher stallion maintains a healthy body condition score (score 5 to 6 on a 9-point scale). To achieve this body condition the pregnancy rates. stallion must be provided with enough energy in their diet, SUMMARY with this energy being derived from structural and non- structural carbohydrates and fats. In addition to energy, The stallion is a seasonal breeder and is mainly active protein, minerals and vitamins should be balanced as they during the breeding season which for most stallions lasts have important functions within the body, especially for from April until October. During the breeding season the production of healthy sperm. 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(2008) Prevalence of obesity in mature horses: an equine body condition study. Journal of Animal Physiology and Animal Nutrition, 92(2): 222. Wolkmer, P., Stumm, A. M. G., Borges, L. F. K., Ferreira, E. P. T., Favaretto, B. & Siqueira, L. C. (2019) Plasma Lipid Peroxidation as a Marker for Seminal Oxidative Stress in Stallion. Journal of Agricultural Science, 11(6): 401-406. Wood, P. L., Scoggin, K., Ball, B. A., Troedsson, M. H., Brennan, K. M. & Squires, E. L. (2017) Lipidomics Evaluation of the Effects of Feeding a Yeast- Based Supplement Containing Algal Docosahexaenoic Acid ( DHA ) on DHA-Containing Glycerophospholipids in Stallion Spermatozoa. Journal of Veterinary Medicine and Research, 4(2): 1078. 32 33Glossary A condition where body fluids have excess base (alkali). This condition is the Alkalosis opposite from acidosis. Organic molecules that combine to form proteins, also known as the building blocks Amino acids of proteins. Anion A negatively charged ion, which means that they have more electrons then protons. A positively charged ion which moves towards negative parts in an electric cell Cation during electrolysis. Chromanol ring Part of the vitamin E structure that is involved in neutralising free radicals. Cutaneous Relating to or affecting the skin. Endocrine Relating to or denoting glands secreting hormones or other products into the blood. Relating to the branch of medicine dealing with incidence, distribution and Epidemiological control of diseases. A polysaccharide stored in bodily tissues which can be transferred into glucose to Glycogen provide energy to the body. Hyperlipidaemia When the blood contains too many lipids such as cholesterol and triglycerides. When the amount of insulin in the blood is higher than what is considered to be Hyperinsulinemia normal. Lipid-soluble The capability of a substance to dissolve in fats, oils or fatty tissues. Electrically charged particle formed by an aggregate of molecules forming a colloidal Micelles particle, helping the body to absorb lipid and fat-soluble vitamins. Non-structural Defined as free, low molecular weight sugars such as glucose, fructose and sucrose. carbohydrates Starch is also a non-structural carbohydrate. Pharmacological aids A substance used to enhance physical performance. A set of observable characteristics of an animal resulting from the interaction of Phenotype genotype with the environment. Progressive motility The percentage of sperm that is mostly moving in a straight line. Saturated tail Tails that have no double bonds in their structure and as a result have straight tails. Molecules that have the same molecular formula but differ in how their atoms are Stereoisomers arranged. Also referred to as ‘fibre’ including cellulose, hemicellulose and pectin which make Structural carbohydrates up the cell wall of the plant. These are digested through microbial fermentation in the hindgut of the horse. Total motility The percentage of sperm making any sort of movement. Unsaturated tail Tails that have double bonds and therefore have no straight tails. 34 35Hungry for knowledge? REPAP DELCYC To get every edition of The JEN ER to your inbox for free, sign up today at %001 feedmark.com/JEN NO DETNIRP You will receive no marketing literature, and you will be the first to receive The JEN! 34 3543 YEARS AT THE CENTRE OF EQUINE NUTRITION 36 PB