Managing and Maintaining the Horse's Body Weight

The body weight of the horse significantly impacts their performance, health, and overall well-being. Maintaining a healthy body weight mainly relies on suitable nutrition. A diet that exceeds or fails to meet the horse's daily needs subsequently leads to being overweight or underweight. Therefore, It is essential to regularly monitor the horse's body weight and adjust the diet when necessary.

An appropriate diet is formulated based on the daily nutrient requirements of the horse, which usually vary between each individual horse. Requirements rely on factors such as the horse's age, overall health, current body weight and the intensity of the daily exercise 1. One of the most important nutrients derived from the diet is energy. Energy is required for body maintenance, several important metabolic processes and provides the body with fuel during exercise 1. When the horse's daily needs are met by feeding a tailored diet, the horse's body weight will remain stable. However, a diet that consistently exceeds or fails to meet daily requirements will result in the horse becoming overweight or underweight 2,3. Too much energy derived from feed will be converted into fat which is stored in body tissue, causing weight gain. When the horse does not receive enough energy to meet the body's needs, the horse will use energy reserves stored in the body, which will eventually cause the horse to lose weight 3. If the horse loses a lot of weight for a prolonged period, this can result in the horse becoming underweight.

Because weighing the horse regularly by using a scale is impractical, their weight is estimated by using the Body Condition Score (BCS). Using a 9-point system, the horse's body weight can be estimated 4. Regularly estimating and monitoring the BCS provides insight into the overall health of the horse and the amount of energy provided to the horse through the diet. A high BCS indicates that the diet contains too much energy and exceeds the requirements of the horse. Conversely, a low BCS indicates that the diet provides too little energy. A BCS between 4 and 6 is considered an ideal score for an adult (sports)horse 5.

Table 1 The Body Condition Score scheme is used to easily estimate the horse's body weight. The scheme, developed by Henneke et al (1983), uses a 9-point system looking at the general condition of the body. This primarily assesses the distribution and amount of fatty tissue in different parts of the body.

Score	Description
1: Extremely thin	No fatty tissue can be felt on the horse The bone structure, ribs and hip are clearly visible You can feel the ribs The horse looks extremely thin
2: Very thin	Moderate amount of fat tissue visible Bones, ribs and hips are visible Ribs can be felt The horse looks thin
3: Thin	Visible fatty tissue around the spine Bones, withers, ribs and hip are slightly covered with fatty tissue Ribs are palpable
4: Moderately thin	The horse is very clearly not too thin The bones are covered with a layer of fatty tissue Ribs are slightly visible and can be felt
5: Moderate	The ribs are not visible but can be felt The horse's neck and shoulders gradually blend into the rest of the body The withers are round
6: Moderate fleshy	Fatty tissue around the ribs, withers and along the neck increases
7: Fleshy	Ribs can be felt but fat can be felt between the ribs Fatty tissue is visible along the neck and withers
8: Fat	The surface along the withers, shoulders and neck is filled with fatty tissue The neck is thicker Fatty tissue along the inner thighs increases
9: Extremely fat	Irregular distribution of fat tissue over the body increases Ribs are no longer palpable

Based on the results and information from monitoring the BCS, adjustments can be made regarding the horse's management to optimise the horse's well-being and performance. Since the requirements differ for each individual horse, it is important to adapt the management to the individual. A horse with a higher BCS score requires different management in comparison to a lower BCS score.

Management of an Underweight Horse

Underweight or weight loss in horses can be caused by various underlying medical issues 3. Therefore, if the horse loses a lot of weight in a short period even if the diet meets the horse's requirements, it is important to have the horse checked by a vet. However, there are also healthy horses with a fast-working metabolism that have difficulty gaining weight or maintaining it. Horses with a fast-working metabolism burn the energy, provided through the diet, quickly. As mentioned earlier, energy is required for maintaining body weight 1. Therefore, enough energy should be provided through the diet to meet the increased requirements of horses with a fast-working metabolism to support and maintain their body weight.

Energy is provided through the addition of carbohydrates, fats and proteins to the diet 1. Carbohydrates and fats are the main energy providers in the diet. Proteins are only utilized as an energy source by horses when their diet lacks sufficient carbohydrates and fats to meet their daily energy needs. 6. This also reduces the amount of protein available for muscle development and maintenance.

Carbohydrates are divided into structural and non-structural carbohydrates. Structural carbohydrates, also known as fibre, are derived from roughage such as hay, silage, grass but also beet pulp. Fibre is digested into volatile fatty acids in the horse's intestines and provides 60-70% of the energy required for physical maintenance and metabolic processes in the body 7. In addition, these fatty acids are important for a well-functioning micro-organism composition in the hindgut 8,9. For more information on the importance of healthy microbiome composition, I would like to refer you to the article "The Importance of Optimal Gut Health". Non-structural carbohydrates, or sugars and starches, come from concentrates and provide the horse with a source of energy that is rapidly metabolised in the body 10.

Research suggests that feeding a high-starch diet is not desirable, due to various health issues this may cause. Therefore, it is important to select nutrients that will provide the required daily amount of energy without adding too many non-structural carbohydrates.

Fats are often supplemented to the horse's diet to support skin and coat and health. In addition to this supporting function, fats are energy-dense nutrients 11. Linseed oil is a product often used to supplement necessary fats to the diet because it is a plant-based product and contains the ideal balance of Omega 3 and Omega 6 fatty acids. Therefore, this product is an ideal supplement and source of energy for horses that struggle to maintain their weight, without the excessive addition of sugar and starch.

Managing an Overweight Horse

Excess weight in horses is linked to health problems such as insulin resistance, laminitis and Equine Metabolic Syndrome (EMS) 12. As mentioned earlier, excess weight in horses occurs when the diet exceeds the horse's requirements. Excess energy that the horse does not use will eventually be stored as body fat 2. To prevent health problems and optimise well-being and performance, diet adjustments should be made to reduce the amount of available energy. However, it is important to introduce dietary changes gradually because the digestive system, especially the microbiome in the hindgut, is very sensitive to sudden dietary changes 13. In addition, it is always important that the diet meets the horse's vitamin and mineral needs.

Concentrated feed is fed to horses to provide necessary vitamins and minerals. Besides, feeding concentrates provide an extra energy source to horses performing intensive activity 14. Ensuring that a horse's diet is in line with their level of physical activity is crucial in preventing weight gain due to a lack of exercise and an excess of concentrates in their diet. Therefore, it is important to monitor the energy intake of the horse through the diet in comparison to the intensity of the physical activity they perform. Horses with little or no physical exertion require less or even no concentrates to meet energy requirements and, for these horses, a vitamin and mineral supplement, in addition to the necessary roughage, is sufficient to meet the horse's needs.

Roughage is important for the health of the equine hindgut and microbiome composition 8,9. Horses naturally eat small portions of roughage throughout the day because the horse's digestive system is unable to digest large portions at once 15. There are various types of roughage, and the amount of available energy varies between them. To address the needs of overweight horses or those that tend to gain weight easily, it is recommended to opt for a type of roughage that is low in energy but still supplies enough fibre to maintain a balanced microbiome. Moreover, this type of roughage can often be fed in small portions throughout the day to prevent digestive problems such as stomach ulcers.

By implementing strip grazing, the horse's access to grass is restricted to a certain amount 16. Especially when the grass is rich in sugar, this is a helpful method to regulate and reduce the amount of available energy from the diet 16. To ensure adequate outdoor time for the horse, consider turning them out in a sand paddock with a hay rack or net filled with low-energy roughage. This can assist in fulfilling their necessities, without overfeeding and ensuring their overall well-being.

Proper exercise is just as important as a healthy diet for a horse to lose weight. Exercise assists in burning excess energy and losing weight 17.

In summary, to ensure a horse's optimal health, well-being, and performance, it is important to first rule out any medical issues if they are overweight or underweight. A veterinarian and nutritionist can provide support, and advice and can help formulate an appropriate diet to achieve this goal.

References

1. Ellis, A. D. (2013). Chapter 5 - Energy systems and requirements. In: Geor, R.J., Harris, P.A., & Coenen, M., (Eds.). Equine Applied and Clinical Nutrition. Saunders Elsevier: China.

2. King, C., & Mansmann, R. A. (2004). Preventing laminitis in horses: Dietary strategies for horse owners. Clinical Techniques in Equine Practice, 3(1): 96–102.

3. Jarvis, N., & McKenzie, H. C. (2021). Nutritional Considerations when Dealing with an Underweight Adult or Senior Horse. Veterinary Clinics of North America - Equine Practice, 37(1): 89–110.

4. Dugdale, A. H. A., Grove-White, D., Curtis, G. C., Harris, P. A., & Argo, C. M. C. G. (2012). Body condition scoring as a predictor of body fat in horses and ponies. Veterinary Journal, 194(2): 173–178.

5. Jensen, R. B., Danielsen, S. H., & Tauson, A. H. (2016). Body condition score, morphometric measurements and estimation of body weight in mature Icelandic horses in Denmark. Acta Veterinaria Scandinavica, 58(1): 20-23.

6. Joh Johnson EL, Duberstein KJ. How to Feed a Horse : Understanding Basic Principles of Horse Nutrition. University of Florida, IFAS Extension, 1-5.

7. Bergman, E. N. (1990). Energy contributions of volatile fatty acids from the gastrointestinal tract in various species. Physiological Reviews, 70(2): 567-590.

8. Raspa, F., Vervuert, I., Capucchio, M. T., Colombino, E., Bergero, D., Forte, C., Greppi, M., Cavallarin, L., Giribaldi, M., Antoniazzi, S., Cavallini, D., Valvassori, E., & Valle, E. (2022). A high-starch vs. high-fibre diet: effects on the gut environment of the different intestinal compartments of the horse digestive tract. BMC Veterinary Research, 18(1): 1-11.

9. Moore-Colyer, M. J. S., Hyslop, J. J., Longland, A. C., & Cuddeford, D. (2000). Intra-caecal fermentation parameters in ponies fed botanically diverse fibre-based diets. Animal Feed Science and Technology, 84(3–4): 183-197.

10. Longland AC, Byrd BM. Pasture nonstructural carbohydrates and equine laminitis. In: Journal of Nutrition, 136(7): 2099-2102.

11. Warren, L. K., & Vineyard, K. R. (2013). Chapter - 7 Fat and fatty acids. In: Geor, R.J., Harris, P.A., & Coenen, M., (Eds.). Equine Applied and Clinical Nutrition. Saunders Elsevier: China.

12. Chapman, S. J. (2015). Obesity and the health and welfare of the leisure horse. The Veterinary Nurse, 5(2): 94-99.

13. De Fombelle, A., Varloud, M., Goachet, A. G., Jacotot, E., Philippeau, C., Drogoul, C., & Julliand, V. (2003). Characterisation of the microbial and biochemical profile of the different segments of the digestive tract in horses given two distinct diets. Animal Science, 77(2): 293-304.

14. Jose-Cunilleras, E., Hinchcliff, K. W., Sams, R. A., Devorand, S. T., & Linderman, J. K. (2002). The glycemic index of a meal fed before exercise alters substrate use and glucose flux in exercising horses. Journal of Applied Physiology, 92(1): 117-128.

15. Métayer, N., Lhôte, M., Bahr, A., Cohen, N. D., Kim, I., Roussel, A. J., & Julliand, V. (2004). Meal size and starch content affect gastric emptying in horses. Equine Veterinary Journal, 36(5): 436–440.

16. Cameron, A., Longland, A., Pfau, T., Pinnegar, S., Brackston, I., Hockenhull, J., Harris, P. A., & Menzies-Gow, N. J. (2022). The Effect of Strip Grazing on Physical Activity and Behavior in Ponies. Journal of Equine Veterinary Science, 110: 1-31.

17. Walshe, N., Cabrera-Rubio, R., Collins, R., Puggioni, A., Gath, V., Crispie, F., Cotter, P. D., Brennan, L., Mulcahy, G., & Duggan, V. (2021). A Multiomic Approach to Investigate the Effects of a Weight Loss Program on the Intestinal Health of Overweight Horses. Frontiers in Veterinary Science, 8: 1-16.6.