“Not all obese individuals are insulin-resistant, and not all IR-affected horses are obese. But IR-associated medical problems are more likely to develop in concert with obesity in individuals born with IR,” said Nat Messer, DVM, Dipl. ABVP, an associate professor of equine medicine and surgery at the University of Missouri, at the 2006 AAEP Convention. “Thus, obesity may be an ‘add-on’ risk factor,” much as obesity in humans contributes to diabetes.

“The obese ‘easy keeper’ is poorly defined scientifically,” said Nicholas Frank, DVM, PhD, Dipl. ACVIM, associate professor of large animal clinical sciences at the University of Tennessee. “Presumably this characteristic is inherited as a difference in metabolism where the horse is able to maintain weight on fewer calories–he’s evolutionarily adapted to live on less food in harsh conditions. When you take this adapted horse and put him on a high-carbohydrate diet (including good pasture), he tends to become obese. Grain can make it even worse.”

The theory of how obesity contributes to insulin resistance is as follows, he said: “The accumulation of lipids (fat molecules or diacylg lycerol) in cells alters the normal signaling events within the cell. Skeletal muscle is the most susceptible to this. The theory is that as animal gets more obese, intracellular lipids interfere with insulin activity. Insulin resistance develops as lipids disrupt insulin receptors. Initially this is a reversible process, but chronic IR causes irreversible damage.”

Get research and health news from the American Association of Equine Practitioners 2006 Convention in The Horse’s AAEP 2006 Wrap-Up sponsored by OCD Equine. Files are available as free PDF downloads