I am not a vet, but have been around horses all my life. Horses colic for a variety of reasons, the most likely cause is their feed. They can colic from moldy hay, hay that is too rich, too much grain, an abrupt change in the type of feed, etc. Horses have a very poor digestive system so when they have any type of problem with their stomach or intenstines it is very serious. When they have colic (a bad belly ache), their first instinct is to lie down and roll around. If they are allowed to do this their intestines can become twisted around one another and then only surgery can fix the problem. Many horses die from this ailment, even if they are given prompt care. It also seems to be true that once a horse colics it is more likely to colic again in the future, so many horses are sold cheap because of their tendancy to do this. Horses are prone to a variety of ailments related to food and exercise, colic is just one of them.