Join Date: Oct 2009
Location: Just south of sanity
Is alfalfa hay the only type of feed he gets, or do you supplement with a grain product?
At his age, the alfalfa may be too rich for him to handle. Like people, the older a horse gets, the less likely they're able to digest rich foods.
Have you had a vet out to do a workup on him? That should be your next step if you change his diet and it doesn't stop the diarrhea.
It could be any number of things, some which are easily fixed, or others that take more than a change of food.