A summary of a few bits of information, some from studies, and some from 20 years of observation;
- Firstly and most importantly (and possibly the hardest point for non-veterinarians to understand; the pathology of the trigeminal nerves that have been examined at post mortem are normal. This does not mean that trigeminal mediated headshaking does not exist; it implies that the condition is caused by a dysfunction (abnormal function) of the nerve rather than by actual damage to the nerve. The reason that this is so significant is that it implies the possibility of returning the physiological state of the nerve to normal.
- Headshaking can develop at any age (the average age of onset is 9)
- Headshaking can develop in any sex
- 50% to 85% of affected horses are geldings but headshaking occurs in mares and stallions as well
- 64% of headshakers are affected seasonally
- Geldings are more likely than mares to be seasonally affected
- Seasonal headshaking tends to be significantly worse on sunny days but improves on rainy days, windy days, at night and indoors. (however, some individuals are made worse by the wind)
- 50% of headshakers only show symptoms during exercise
- Horses who are overweight are over-represented (are more likely to develop headshaking)
- Having a period of layup (a period when the horse is out of work) may contribute to onset of headshaking
- Some horses in "remission" can be stimulated out of this remission by an electric shock, such as from an electric fence
- Some horses do "outgrow" headshaking. After headshaking for several years, they stop. This may occur in as many as 20-30% of cases based on some observations
- Some horses have headshaking symptoms so severe that following failed attempts to treat with existing medications, because of welfare issues, the horse has been humanely euthanised
Common misconceptions about headshaking; True or False?
1. The nerve in horses with headshaking syndrome is damaged.
2. A true headshaker shakes its head constantly.
- Headshaking occurs to varying degrees
- In some rare cases horses only headshake during the process of consuming hay and improve dramatically if switched to a soaked pelleted feed
- Many horses start and stop headshaking at different times of the year (some start in the fall and stop in spring, while most start in the spring and stop in the fall); this pattern is repeated each year in the same horses.
For example; the owner of one horse that was in our study felt that the onset of headshaking was associated with vaccination as the horse was vaccinated in April, just before the onset of the behavior. The following year no vaccinations or medications were administered, yet the behavior began in the same calendar week. This fits the theory that normal physiological seasonal events are associated with the onset of seasonal headshaking.
Don’t forget your horse sheds in the springtime and grows hair in the fall, both are seasonally related. Many physiologic changes occur during the year. For example, studies on ACTH and adrenal feedback loops in horses are distinctly different at different times of the year. Seasonal changes in reproductive hormone levels, even in geldings, are very dramatic. We have much to learn about the endogenous changes that occur seasonally in the horse, and how they relate to headshaking.
3. Is headshaking contagious?
4. Are the symptoms of headshaking related to the Rhino Virus or vaccination?
5. My friend's horse was normal one day and then suddenly showed symptoms while warming up before a competition the next. Is this possible?
It is not uncommon for headshaking symptoms to begin quite suddenly (your veterinarian would call this "acute onset").
6. I can not identify any triggers. Is this common?
Despite the fact that many owners understand what triggers episodes in their horses, there are many who are unable to identify the triggers for their horse's headshaking.
7. Has there been ANY progress in finding a treatment or cure?
We are doing research directed toward finding the cause of headshaking so that an effective cure for this condition can be developed. Research is time consuming, expensive, and painfully slow. We could do more if we had more funding.
8. Is there a surgical procedure that can help with, or fix, this condition?
There is currently no surgical procedure that has been shown to consistently correct the syndrome.
There is some research taking place in England that involves surgical implantion of metal coils around the trigeminal nerve which are said to blunt the nerve firing.
9. Would a radiograph (x-ray) of the skull or a scoping of the nasal passage be beneficial? Visit the "How Can My Vet Help?" page.