Research Reference:

Bulmer, Louise S et al., 2019. High-starch diets alter equine faecal microbiota and increase behavioural reactivity. Scientific reports, 9(1), pp.18621–11.

The equine digestive tract is better suited to a high fiber-fat low starch diet. This type of diet results in healthier microbial populations within the intestines and results in a more settled pattern of behavior. Horses are designed to eat small amounts more frequently mimicking grazing/trickle feeding behavior.