Overweight Horse? Microbes May Be Partially to Blame

The perils of obesity in horses are increasingly understood, yet approximately 30% of horses in the United States, United Kingdom, and Scotland are estimated to be overweight or obese. Overconditioned horses have decreased reproductive and athletic performance and are at risk for insulin resistance and laminitis.

Obesity, in general, stems from horses consuming more energy than they require. Frequently horses become obese secondary to being offered concentrate feeds that aren’t necessary to maintain moderate body condition. Some horses can become obese on pasture alone.

What makes some horses more likely to become obese than others? One group of researchers* explains the population of microscopic organisms that help break down fiber in the large intestine differ from horse to horse. Microbes capable of fermenting fiber produce volatile fatty acids, which are used for energy. In sum, a horse having an abundance of fiber-fermenting microbes could be more likely to pack on the poundage compared with a horse that has fewer fiber-fermenting microbes, despite the same diet.

To more definitively determine if the microbes in the hindgut do explain, at least in part, why some horses are obese, the research group compared the microbes in obese and nonobese mares and measured the volatile fatty acids produced by those microbes.

Although no difference in specific microbe populations included in this study was identified between obese and nonobese mares, one particular volatile fatty acid, acetate, was higher in the bloodstream of obese mares. The authors concluded, “The cause and significance of this finding should be further explored as a mechanism linking obesity and gut microbes.”

*Shepherd, M.L., M.A. Ponder, and A.O. Burk. 2014. Fibre digestibility, abundance of faecal bacteria and plasma acetate concentrations in overweight adult mares. Journal of Nutritional Science 3:e10.