Horses get three types of epilepsy. One type is just called epilepsy; the others are benign, or neonatal, epilepsy and idiopathic epilepsy. Some foals and young horses grow out of neonatal or regular epilepsy but it is not known why. Horse Owner's Veterinary Handbook suggests that this could be due to genetics. All three types produce similar symptoms.
Unless they have idiopathic epilepsy (which means the cause of that horse's epilepsy is unknown), horses with epilepsy usually will be under four years old. Arabians are the only breed known to suffer from neonatal epilepsy. Symptoms can develop anytime after birth to weaning. According to Current Therapy in Equine Medicine, Arabian foals, especially of the Egyptian Arabian variety, usually stop having symptoms by the time they are yearlings.
The main symptom of horse epilepsy is seizures. This can vary from just an uncontrollable twitching of the head and jaws to the horse collapsing on its side, thrashing about. The horse may spin awkwardly in a circle. The eyes often roll up into the head, showing just whites. The jaw will often bite uncontrollably, so keep away from the mouth. The horse will often lose consciousness for less than five minutes. The horse also may defecate or urinate suddenly.
In neonatal epilepsy suffered by some Arabian foals, the seizures can be dramatic. The foal will look twisted and do a frantic swimming motion with the legs. Often the head and neck will arch as far over the back as possible, as if someone were pulling on the head with an invisible rope. It's usually all over in 60 seconds.
In equine epilepsy, the horse usually has a post-seizure period of acting depressed or extremely tired. Sometimes the horse will seem to be blind or will stand still with head lowered in a kind of stupor. This usually lasts for several hours after the seizure. Horses with some other conditions that cause seizures, such as severe colic, will not go through this phase.
Epileptic seizures in horses are nearly the same as seizures resulting from other medical conditions, such as narcolepsy (where the horse falls asleep or collapses uncontrollably), long bone fractures, poisoning, severe colic, encephalitis, hypocalcaemia (where the calcium in the blood suddenly drops) or hyperkalemic periodic paralysis ( a genetic muscle disease in stock horse breeds). It is important to get the horse properly diagnosed by a vet in order to get the right treatment.