The amount of energy in the diet is reduced to facilitate weight loss and the non-structural carbohydrate (NSC) content of the diet is lowered to reduce the glycemic response. Obese horses and ponies should be provided a low NSC grass hay diet with mineral/vitamin supplementation. The NCS content of hay can be determined by submitting a sample for nutrient analysis. In horses that are being overfed, removal of all grain from the diet is sometimes sufficient to induce weight loss. An obese horse should be fed 1.5 lbs of hay per 100 lbs body weight.
Until insulin sensitivity improves, horses should be restricted from pasture. Mildly affected horses can return to pasture once obesity and insulin resistance have been addressed, but care must be taken to restrict pasture access during changing growth phases such as the rapid growth phase of spring or preparation for cold weather during the fall. Strategies for limiting grass consumption include short (<1 hour) turnout periods (or hand grazing), confinement to a small paddock, and/or the use of a grazing muzzle. Unfortunately, severely insulin resistant horses with recurrent laminitis are best kept off pasture permanently.
Regular physical activity improves insulin sensitivity. With the exception of horses and ponies painful due to laminitis, an increase in exercise is recommended to improve insulin sensitivity and promote weight loss. A general recommendation is to start with 20-30 minutes of riding and/or longeing 2-3 times per week with a gradual increase to 5 sessions per week.
Most horses and ponies with EMS can be effectively managed with changes in diet and exercise. However, weight loss can be induced and insulin sensitivity improved by administering levothyroxine sodium (thyroid hormone). However this is only an appropriate treatment in certain circumstances and should always be prescribed and monitored by a licensed veterinarian.
*This project was supported by Agriculture and Food Research Initiative competitive grant no. 2009-55205-05254 from the USDA National Institute of Food and Agriculture Animal Genome Program.