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Feeding Horses with Equine Metabolic SyndromeBy Kentucky Equine Research Staff · August 4, 2014

Planning a diet for a horse with equine metabolic syndrome (EMS) depends on how severe the insulin resistance is and how obese the horse is. Most, but not all, horses with EMS are obese, and those that are not obese must be managed differently.

For obese horses with EMS, intake of nonstructural carbohydrates (NSC) should be controlled, as this can reduce glucose and insulin responses to feeding. Grazing should be eliminated or drastically reduced until obesity and insulin resistance are moderated, and some equines with recurrent insulin resistance will never be able to graze freely. Particular care must be taken to keep susceptible horses off pasture during periods of rapid growth, after cold nights, during sunny days, and when grass is stressed by drought or overgrazing, as these are times when NSC levels rise.

Forage NSC should be 10 to 12% of the dry matter or less to reduce the risk of hyperinsulinemia and laminitis. Hay intake needs to be restricted to help with weight loss, and NSC content should be tested and the hay soaked if necessary to lower NSC levels. No grain concentrates or treats should be fed other than a low-intake, low-calorie source of nutrients such as a balancer pellet or a vitamin and mineral supplement. Obesity is characterized by oxidative stress, and an antioxidant supplement is recommended.

Non-obese horses with EMS need energy for work, so the aim is to supply increased energy intake with low glucose and insulin responses after feeding. This can involve the use of commercial feeds with a moderate NSC content of less than 18 to 22% NSC as fed, or the addition of foodstuffs with a low glycemic index such as soaked beet pulp, soaked soy hulls, oil, and stabilized rice bran. These can be added to the diet of forage and a balancer pellet. Alfalfa (lucerne) hay or chaff may be fed to these horses, as the higher energy content is valuable and its NSC content is often lower than grass hay. Protein content of the diet has not been shown to influence insulin dynamics. Feed management measures to reduce glycemic and insulinemic responses to feeding are useful, such as multiple small meals, obstacles in the feed bin to slow the intake of feed, and feeding hay after concentrates.

High fat diets have the potential to worsen or create insulin resistance, as shown in a study at Kentucky Equine Research. In the study, a diet with 30% of digestible energy supplied as fat significantly impaired glucose tolerance in aged, non-obese horses compared to a more traditional diet. Moderate carbohydrate intake (31% of digestible energy supplied as NSC) improved glucose tolerance during intravenous glucose tolerance tests compared to both a high fat and an all grass hay diet. The addition of 60 mL of fish oil to the diet of aged horses that were not insulin resistant improved glucose clearance in the high fat model compared to a corn oil control. Small doses of fish oil could be beneficial for obese horses with EMS as it will not contribute many calories and could be fed to the non-obese horse to counter the negative impact of higher amounts of regular vegetable oil on glucose tolerance.