Equine Obesity

Introduction
Obesity is a growing welfare issue in the horse world, and has even been recognized as an epidemic by some authors (Giles et al, 2014; Sillence, 2012). Sillence even says that horse owners have difficulty recognizing when a horse is overweight. Because weight, body condition score (BCS), and level of activity are all very important factors in determining what nutrients a horse needs to live a healthy life, a lack of understanding among owners about the condition of their horse means that many horses do not receive proper nutrition. Estimates have set the number of obese horses (defined as those scoring 8 or 9 out of 9 on the Henneke scale) at 45% of the equine population in developed countries (Johnson, 2009), while other studies have set the number at 27 to 35%, depending on the season (Giles et al, 2014).

Johnson (2009) recognizes that it is natural for a horse to gain and lose weight throughout the year. The gain usually occurs during the late summer and autumn, and is in response to proopiomelanocortin (POMC) peptides produced by the hypothalamic-pituitary axis. These peptides also govern the growth of a winter hair coat (Johnson, 2009). Both the thickened coat and the increase in body fat stores are designed to prepare the horse for winter, when food will become more scarce. This is an invaluable resource for the undomesticated horse, and it is likely the only reason some of them survive without human help. These fat stores should be used up by spring (Johnson, 2009), and the horse will again be in proper condition. But in the domesticated horse, which has a regular and plentiful supply of food year-round, this yearly reserve of fat is unnecessary, and over the winter, the horse often does not lose the weight it gained during late summer and autumn, resulting in an overweight horse come spring.

Clinical Signs
Obesity is a relatively easy condition to combat, because with a little knowledge, it is simple for anyone to recognize. The sooner it is recognized, the less traumatic treatment will be, both for the horse and the owner. Using the Henneke Body Condition Scoring system (Easley, 2009), an owner can feel the horse all over and rate the amount of body fat present on each major section according to the assessment details. Averaging these figures will provide the horse’s overall body condition score. From there the owner, advised by their veterinarian or nutritionist, can take action. If the horse’s score is 7, it is considered overweight. Scores of eight and nine, however, are both classed as obese by Giles (2014), because it is very hard to tell the difference between the two. While scores of 7, 8, and 9 are all undesirable, 8 and 9 are dangerous.

Effects
Many other health problems are caused, in part or in whole, by obesity (a score of 8 or 9). An obese horse is more likely to have equine hyperlipemia (NRC, 2007), insulin resistance which can lead to laminitis (Johnson, 2009; Hoffman et al, 2003), developmental orthopaedic disease, which is also called osteochondrosis (Johnson, 2009), pituitary pars intermediary dysfunction, known as PPID (Johnson, 2009), and osteoarthritis (Giles et al, 2014). Obese horses are even prone to liver and kidney damage (NRC, 2007), which, along with the other diseases listed above, will affect the horse for its lifetime, even if its weight is later returned to an acceptable or ideal level.

Cause
Johnson (2009) makes it very clear that the cause of obesity in domesticated horses is the management practices it is subjected to, but there are also some genetic and environmental factors over which the owner has no control that can place a horse at risk of becoming obese (Giles et al, 2014). Older animals, those with an injury, and certain breeds have a higher risk of obesity unless they are carefully managed (Giles et al, 2014). Breeds that are easy keepers, or do not require high quality, high quantity feed can easily receive more protein and energy than they require, resulting in fat stores. When an older animal stops working or growing, or the horse is injured and cannot work, often their ration is not adjusted accordingly, and they begin receiving too much energy, non-structural carbohydrates (NSCs), starch, and protein for their needs, resulting in weight gain (NRC, 2007; Johnson, 2009). Proper ration balancing according to the individual horse’s needs is therefore important.

Management Strategies
There is not much agreement amongst scientists about how to remedy obesity. The Blue Cross for Pets (n.d.) provides the advice of reducing the obese horse’s ration to 1.5% of their ideal body weight, tweaking the ration regularly thereafter as needed according to BCS and weight reassessment. They recommend reassessing weekly, as well as increasing the horse’s physical activity. Getty (n.d.), Curtis et al (2011), Dugdale et al (2010), and Argo et al (2012) all agreed with the basic points made by Blue Cross concerning adjusting the horse’s ration and providing exercise. But they all disagreed about how best to approach this.

 

All of the studies also advocate an increase in the horse’s physical activity to complement the diet, when possible. But since owners often don’t recognize obesity until it is too late and the horse has foundered or has developed another disease which prevents them from moving comfortably, exercise is not an option for these horses. In these cases, the diet alone must be relied upon to reduce the horse’s weight to an ideal level. Kentucky Equine Research (2015) suggests soaking the affected horse’s hay for half an hour to an hour. This will not affect fibre levels, but will leach out some excess carbohydrates, making the hay healthier for the overweight horse. If no results are achieved from a diet and exercise program, Geor (2007) suggests treatment with levothyroxine sodium, which increases cell metabolism, encouraging weight loss, but he notes that this is a last resort.

Once weight has been reduced, it is important to keep the horse at that level and not let its BCS slide up the scale again. The Blue Cross for Pets advises continual monitoring of the horse’s BCS, with adjustments to feed and exercise as needed to maintain weight. And Argo et al (2012) maintains that educated owners are less likely to have obese horses. Every owner should know how to use the BCS system, and should know the risks associated with obesity. Veterinarians and nutritionists play a vital role in keeping horses healthy, but obesity is an often overlooked disease that can have serious consequences. This epidemic can be stopped!

Take-Home Points

  • Obesity is a growing welfare issue in well-developed countries.
  • 27 to 35% of the equine population in developed countries is overweight (Giles et al, 2014)
  • Obesity can cause a wealth of other health issues, some of which are debilitating.
  • Obesity is largely caused by the management of horses, particularly the overfeeding of certain nutrients.
  • Starch, NSC, sugars, protein, and energy in excess of horse requirements can cause obesity.
  • Some breeds of horses are more susceptible to obesity, and must be managed more carefully than others.
  • A careful diet of feeds high in fibre combined with exercise can help to reduce weight slowly to an acceptable level.
  • Restricting the diet too much causes an enormous amount of stress, creating another welfare issue.
  • A restricted diet results in a 1% reduction in weight per week.
  • Horses on a restricted diet may begin to eat things that are not edible, resulting in a decrease in efficacy of the diet, and potential harm to the horse.
  • Growing horses and aging horses need to be managed differently than those in the prime of life, as growing horses need a lot of energy, and aging horses tend to lose weight easily.
  • Emaciation is just as dangerous as obesity, so as the horse begins to lose weight, the diet must be kept carefully controlled so too much weight is not lost.
  • Once the horse is at an acceptable BCS, the diet must be modified to suit its maintenance requirements, or weight will continue to be lost.
  • Knowing how to use body condition scoring and applying it to the horse regularly can catch issues early so treatment is easier.

References:
Argo, C; Curtis, G; Grove-White, D; Dugdale, A; Barfoot, C; Harris, P. (2012) Weight loss resistance: A further consideration for the nutritional management of obese Equidae. The Veterinary Journal, 194(2): 179–188. http://journals2.scholarsportal.info.subzero.lib.uoguelph.ca/pdf/10900233/v194i0002/179_wlrafctnmooe.xml.

Blue Cross for Pets. (undated) Horse Obesity Prevention and Management. Accessed June 6, 2016. https://www.bluecross.org.uk/pet-advice/horse-obesity-prevention-and-management.

Curtis, G; Barfoot, C; Dugdale, A; Harris, P; Argo, C. (2011) Voluntary ingestion of wood shavings by obese horses under dietary restriction. British Journal of Nutrition, 106(Suppl 1): S178–S182. http://journals.cambridge.org.subzero.lib.uoguelph.ca/download.php?file=%2FBJN%2FBJN106_S1%2FS0007114511000547a.pdf&code=fb0786389c6c17a8417e3dfa463249ff.

Dugdale, A; Curtis, G; Cripps, P; Harris, P; Argo, C. (2010) Effect of dietary restriction on body condition, composition and welfare of overweight and obese pony mares. Equine Veterinary Journal, 42(7): 600-610. doi: 10.1111/j.2042-3306.2010.00110.x. http://onlinelibrary.wiley.com.subzero.lib.uoguelph.ca/doi/10.1111/j.2042-3306.2010.00110.x/epdf.

Easley, R. Body Condition Scores: The Henneke System. http://www.gerlltd.org/Education/Equine%20Body%20Condition%20Score%20Presentation.pdf.

Geor, J. (2007) Management of obesity and insulin resistance in horses. Journal of Animal Science, 85(Suppl 1):205.

Getty, JM. (undated) Restricting Forage is Incredibly Stressful; Choose a different method to help your horse lose weight. Getty Equine Nutrition. Accessed June 6, 2016. http://gettyequinenutrition.biz/Library/RestrictingForageisIncrediblyStressful.htm.

Giles, S; Rands, S; Nicol, C; Harris, P. (2014) Obesity prevalence and associated risk factors in outdoor living domestic horses and ponies. PeerJ. 2014 Mar 20;2:e299. DOI 10.7717/peerj.299. https://peerj.com/articles/299.pdf.

Hoffman, RM; Boston, RC; Stefanovski, D; Kronfeld, DS; and Harris, PA. (2003) Obesity and diet affect glucose dynamics and insulin sensitivity in Thoroughbred geldings. Journal of Animal Science, 81(9): 2333-2342.

Johnson, P; Wiedmeyer, C; Messer, N; Ganjam, V. (2009) Medical Implications of Obesity in Horses—Lessons for Human Obesity. Journal of Diabetes Science and Technology, 3(1); 163–174. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2769846/.

Kentucky Equine Research. (2015) Fighting Equine Obesity: Some Practical Suggestions. Equinews, Kentucky Equine Research Nutrition and Health Daily. http://brooks.equinews.com//article/fighting-equine-obesity-some-practical-suggestions.

National Research Council. (2007) Nutrient Requirements of Horses. Sixth Revised Edition. The National Academies Press, Washington, D.C. ISBN-10: 0-309-10212-X (cloth)

Sillence, MN. (2012) ‘Supersize me’: On Equine Obesity. The Veterinary Journal, 194(2): 137–138. http://www.sciencedirect.com/science/article/pii/S1090023312003450. doi:10.1016/j.tvjl.2012.08.004

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