When humans get diarrhea, it’s usually not a big deal. Unpleasant, yes, but most cases resolve in a day or two. Dogs – especially those prone to eating whatever they find – are much the same: a few messy and uncomfortable hours and they are healthy again. (Of course, diarrhea can also be a symptom of something more serious, but most cases are not.) With horses, however, diarrhea – especially when the horse also has a fever – can signal that the animal is suffering from colitis.