Q: Does hay give horses colic?
A: Hay diets (horses should receive at least 2/3 of their nutrition from forage, i.e., hay or pasture) tend to lower the risk of colic (horse on pasture pose the lowest risk). Good quality hay (free of dust, mold, weeds, and other foreign matter) should not give horses colic.
However, quickly changing hay types or qualities (i.e. changing quickly from a grass hay to an alfalfa hay) can induce colic, along with hay that is weedy, dusty or moldy. Several things can induce colic in horses, but quality hay is not usually one of them.
By Martinson, PhD, & Malone, DVM, University of Minnesota