Sometimes occurring as a stand-alone, or going hand-in-hand with PPID, horses experience insulin dysregulation with high resting insulin blood levels, abnormal insulin responses to feeding and glucose administration, and tissue insulin resistance. This condition is most prevalent in overweight or obese individuals such as those that have developed equine metabolic syndrome (EMS) due to an excess intake of starch and sugars from too many calories. However, not all obese horses are insulin dysregulated and not all insulin dysregulated horses are obese.
Obesity is associated with chronic inflammation and insulin dysregulation, and these developments can lead to laminitis and/or osteoarthritis.
The objective in managing insulin dysregulation is to improve insulin sensitivity by feeding calorie-restricted diets with low non-structural carbohydrates (NSC) and implementing regular exercise regimens. An obese horse should be fed with a weight loss target. This usually entails offering 1.5% of its body weight in low-NSC (<12%) hay, i.e. about 15 pounds for a 1,000-pound horse. Use a scale to weigh the hay to ensure that no extra is fed. To reduce the sugar content of hay, soak it in water for 30-60 minutes, then pour off the supernatant to remove the dissolved sugars.
A horse with insulin dysregulation should be kept off pasture since pasture grasses are rich in fructans (sugars) and carbohydrates, especially when grass is stressed by drought or frost, and also at certain times of the day, like afternoon hours. Pasture grass is also at its richest in NSC after a rain, during rapid spring growth, and as it enters winter dormancy in the fall. Either restrict access to pasture altogether or only turn out for an hour or two with a grazing muzzle during the early morning hours. Do not offer supplements such as grain, complete feed products, or molasses-containing products. The only safe supplement to feed is a low-NSC feed that is commercially prepared with the insulin-resistant horse in mind.
Molasses-free beet pulp soaked in water provides some nutrition and fiber, and rice bran or vegetable oil provide useful calories for horses that aren’t necessarily obese but do suffer from insulin dysregulation.