Horses produce body heat when they chew and digest feeds. This internal body heat aids in keeping them warm in cold weather. But some feeds produce more body heat than others. In fact, some feeds produce little body heat. Fats, commonly added to horse rations today as an energy source, don't produce much body heat during digestion.
Fibrous feeds produce the greatest amount of body heat during the digestive process.
Hays, which are commonly fed to horses in winter since pasture isn't as readily available, produce considerable body heat. Oats, which has a fibrous hull, also produces body heat. Corn, a low-fiber feed, won't produce much body heat. This is in contrast to what some horse owners think. Some owners think that corn is a winter feed, and oats is a summer choice.