Despite the fact that horses evolved on a forage-based diet that is high in fiber and low in calories, some horse owners and trainers just can't resist feeding a low-fiber, calorie-dense diet.

"Horses are grazing animals," explains Katherine A. Houpt, VMD, PhD, Dipl. ACVB, a professor emeritus of Cornell University's College of Veterinary Medicine. "When they are denied access to pasture to partake in this natural activity, health and behavior issues arise, like the development of gastric ulcers and destruction of wood fences and stall walls."

To determine if horses' welfare, in addition to their health, was compromised when denied fiber, Houpt and co-author Jaime Elia assessed the "motivation for fiber" of eight mares fed two different diets, either orchardgrass hay ad libitum or a complete pelleted feed, for three weeks. The horses were also trained to press a panel to obtain a food reward.

"We found that when horses were fed pellets, they worked harder to obtain a hay food reward than when they were fed hay," said Houpt