Equine Metabolic Syndrome

By Horse & Hound Veterinary Services | Jan 04, 2010

Equine metabolic syndrome (EMS) is a term used by horseman and veterinarians alike to describe a group of clinical signs that may accompany pasture-associated laminitis or "founder". It is defined by evidence of insulin resistance, obesity or regional fat deposition, and previous or existing laminitis. In the past signs of EMS were attributed to hypothyroidism (low thyroid hormone), but it is now recognized that low resting thyroid levels accompany many systemic diseases in the horse.  Broadly defined, insulin resistance is a decreased response of the animal's tissues to circulating insulin, resulting in decreased uptake of glucose (sugar) by skeletal muscle, fat, and liver tissue.  EMS has been identified in many breeds of horses, ponies, and donkeys.  Most equids are 5 - 15 years of age when laminitis first occurs.  Physical characteristics include generalized obesity or development of regional fat desposits (cresty neck, fat at tailhead) or both and laminitis.  These horses may be at greater risk to colic due to pendulous lipomas (fatty tumors) within their abdomen.  Obese horses with EMS are often described as "easy keepers" because they require fewer calories to maintain optimum body weight. Factors that may contribute to the development of EMS include grazing on lush pasture, feeding concentrates and interference with seasonal weight loss. Overfeeding horses promotes obesity. Some concentrates (sweet feed) induce weight gain and also exacerbate insulin resistance (IR). Currently it is believed that laminits in horses with IR is caused by excessive soluable carbohydrates (similar to humans with type II diabetes mellitus) and the secondary alterations in the gut microflora. If you suspect your horse may be suffering from EMS, your veterinarian can test the horse or pony for resting serum insulin concentration or perform a glucose-insulin test. The glucose-insulin test is very labor intensive and is usually done in a hospital setting. Equine obesity can be managed by limiting caloric intake and eliminating the horse's access to pasture until the animal has reached ideal body condition. Concentrates should be eliminated and hay limited to 1.5% of the current body weight (15 lbs. for 1000 lb. horse). The hay fed should contain less than 12% simple sugars for obese IR equids. For hay greater than 12%, you can soak the hay for 30 mins. in a large tub, drain off the water, then feed the moistened hay only. There are now commercially available feeds (Purina) specifically made for IR horses.  If horses are not allowed access to pasture eating, they should be fed 1000 IU of vitamin E supplement. Vet-A-Mix, division of Lloyd, Inc., produces "Target IR" a vitamin-mineral supplement designed to give nutritional support to IR horses in dry lots on hay only diets. This product may be purchased through licensed veterinarians only. Insulin resistance can be managed by controlling body weight, routine exercise, and avoiding feeds that exacerbate the condition. Thyroid supplementation can be used to induce weight loss and improve insulin sensitivily in horses.  It should be used in horses when the animal cannot be exercised or laminitis threatens to cause permanent damage to the hoof integrity. Be sure to speak with your veterinarian before attempting to treat a horse you suspect of having IR and EMS. 

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