Hay diets tend to lower the risk of colic, or intestinal pain, in horses, according to a recent issue of the University of Minnesota Horse Newsletter. Good-quality hay free of dust, mold, weeds and other foreign matter should not give horses colic. However, quickly changing hay type or quality, such as from grass hay to alfalfa hay, can induce colic. Weedy, dusty or moldy hay or feed can also induce colic. The University of Kentucky Cooperative Extension Service says other causes of colic can include intestinal obstructions, intestinal parasites, diseases or twisted intestines, among others. University of Minnesota equine experts suggest that horses should get at least two-thirds of their nutrition from forage. Horses on pasture are said to face the lowest colic risk.