Ask the Vet: Equine Seizures

Dear Dr. Lowder: My name is Susan. I live in northwest Pennsylvania approx. 15 miles from the New York State line. I own a 22-year-old saddlebred mare who began having "fainting spells" during the summer of 2001. The first incident was in July when I was getting ready to trail ride. As I adjusted her saddle, she suddenly started to tremble in her front legs, lost her balance in her hindquarters and fell violently over on her side. She recovered fairly quickly; we were able to remove the saddle before she stood up again. The very same behavior occurred again in late August or early September. Again, we were getting ready to ride but had to abandon our plans.

Story originally posted by: Michael Lowder, DVM, MS

The third incident, early October 2001, was similar but occurred in her stall when the stable owner entered it to check her mouth for possible sores. As soon as she was approached, she began to quiver, lose her balance, and collapsed right in her stall. The stable owner already knew about the previous episodes and safely exited the stall. After crashing around for a few minutes in the stall, my horse got up and seemed OK. Everyone was a nervous wreck by then and strict orders were given that no one was to handle my horse except me and the stable owner and her staff.

The final and most frightening episode with my horse was on or about October 29, 2001. I was free-exercising my horse in our covered arena and getting ready to return her to her stall. She was calm and quiet. Just as I was speaking to the stable owner, my horse suddenly raised her head, stiffened up, her front legs began to tremble and she started falling backwards. This time, however, she flipped over on her side with such violence that her head hit the ground rather hard and blood dripped from her nose. Her entire body became stiff and her legs were straight out from her body. We thought she was dead! After a few minutes, she seemed to relax somewhat but was unable to stand up. In fact, she struggled to get into an upright position. Finally, she was able to right herself into an upright position. She laid upright for approx. 15 minutes or more and eventually was able to stand. She was very disoriented, off balance, and stumbled around as though she was drunk. She looked dazed and “far away.” Soon after standing up, she had a bowel movement. As time passed that day, she gradually became less disoriented and returned to somewhat normal behavior (quiet, eating, and drinking).

My stable owner has a niece who suffers from epilepsy. Her comment to me that day was that Rose, my horse, seemed to exhibit the classic symptoms of a grand mal seizure.

We contacted our local large animal vet, who does not really specialize in horses, and he suggested we start her on Phenobarbital in an attempt to quiet the activity in her brain that could be causing these seizures. We are 3 1/2 hours from Cornell University and I was very reluctant to trailer my horse where a full exam could be performed. If she went down while in the trailer, the result could have been disastrous for her and the driver of the trailer. We could only really feel our way along with her. My vet stated he had no experience with this type of problem in horses, but had seen it in dogs.

Now we get to this year. My horse did well on the Phenobarbital over this last year. In time, we gradually reduced her dosage from 40 tabs per day, then to 20, then finally, 10. In mid-July of this year, we stopped the dosage completely. Everything seemed fine. No symptoms of seizures had ever been seen during the entire past year.

Then on November 9th, my horse experienced the same seizure behavior. Once again, we happened to be in our covered arena. All I was doing at that moment was wiping her face off with a towel (she has a chronic problem with her eyes draining/tearing). Suddenly, her head went up, her front legs began to tremble, and she started falling backwards onto her hindquarters. Once again, she fell over onto the ground. As with the very first incident, she recovered very quickly and seemed OK. I refer to this type of episode as a petite mal seizure. Based on a recent eye injury on her left side, however, we believe she may also have had a spell out in our pasture – one of the stable workers had seen her “rolling near the fence” about a week and a half prior to this. If that is indeed the case, then it would have been almost exactly one year to the day when she had her “grand mal” seizure!

I discussed the episode with my vet, and he suggested that we not medicate her just yet because he wanted to find out if the seizures happen only occasionally, or if they occur more frequently (several times a week etc). She has been confined to her stall with daily turnout in the covered arena. So far, she has had no repeat episode that anyone has observed.

My questions to you is this: Can you offer any type of explanation as to why a mare of this age, with no real medical problems prior to this, suddenly develops this type of “idiopathic” seizure? My vet had run 2 blood tests, one in November, 2001, and another in June, 2002, and found nothing out of the ordinary even with the anticonvulsant medication she had been taking all that time. As far as I know, there are no toxic plants or trees in our pasture/turnout area. However, it is partially wooded. If she was eating something toxic, wouldn’t the other horses also be exposed and exhibiting the same behavior?

I would give anything to understand what has happened to my horse. She is such a sweet kind animal. It’s bad enough I can no longer ride her, but I’m not sure she should even go out to pasture for fear she’ll fall and injure herself.

PLEASE, DO YOU HAVE ANY IDEA OR EXPERIENCE WITH THIS TYPE OF BEHAVIOR? We just don’t have anyone locally who can help me. What advice can you offer for our consideration? Should I have my vet contact you with his findings?

Thank you for replying to my letter.


First, I would suggest you take your horse to Cornell and let one of the internal medicine people take a look at her. Second, your mare has the potential to be harmful to you and others and you need to think about the liability of keeping a mare like this. Thirdly, prior to taking the horse anywhere you need to make sure you want to spend the money to try to find a diagnosis. In the end, you may not be able to. There may be a tumor growing.
Dr. Lowder