A study at the Maxwell Gluck Equine Research Center at the University of Kentucky, reported in the Journal of Reproduction, Fertility and Development, looked at the effects of treating obese insulin-resistant mares with Metformin — an oral medication used to control high blood sugar in diabetic humans.
It’s has been known for quite a while that overweight mares tend to continue to cycle over the winter, when leaner mares don’t, and that these overweight mares are insulin-resistant compared to more slender mares. Mares were given 3, 6 or 9 grams of Metformin per day. The study found improved insulin sensitivity after one month in the mares given 3 grams/day, but no effect with 6 or 9 grams per day at one month, and when tested two or more months after starting the 3 grams/day dose there was no longer any improvement seen. It was determined that the drug Metformin had no real, long-lasting effect for these horses.
Feeding a diet low in simple sugars and starches coupled with careful mineral balancing, with regular exercise unless the horse is already laminitic, remains the most, in fact only, effective treatment for insulin resistance in horses. Watch for our upcoming article on diagnosing and managing insulin-resistant horses.