ACushing’s disease is caused by a tumor or hyperplasia of part of the pituitary gland. Sometimes the pituitary gland becomes enlarged, but often it is not physically enlarged, just producing larger amounts of hormones than usual. (A complete summary of Cushing’s is online at TheHorse.com/12534.)

Seizures are rare in the horse, and adult horses especially have a high seizure threshold. Cushing’s disease can cause seizures, but they are very rarely seen with this disease. It is hard to say for sure why some Cushing’s horses have seizures, but it might be from associated liver disease (sometimes seen with Cushing’s), hyperglycemia (high blood sugar, which is common in Cushing’s), or from the pituitary gland becoming enlarged with the tumor and compressing other structures of the brain (as mentioned above, not normally seen with Cushing’s). I have worked with a number of horses with Cushing’s, and none had seizures.

Your horse sounds a bit unusual to me. If he has not had a laboratory diagnostic test for Cushing’s, then I would recommend you get one. If he truly did have a seizure and that seizure is associated with Cushing’s, then you need to get him on appropriate medication.