(The following is edited for anonymity and clarity.)

The post reads...

We have a new horse for my son. When we purchased him, he only tossed his head (as if a fly was bothering him) for 5 minutes or so, then he was fine. We had two weeks of non stop rain and in that time "off", he is doing this worse.

We had his teeth checked, a couple baby teeth pulled so that permanents would be straight and had his teeth floated and the problem persists. We have no problem getting the bridle on, He stands quietly when you're not asking him to do anything.

As soon as my son mounts, he starts the shaking. Sometimes the shaking is like a pulling affect, other times like a "no, I don't want to work"

During a lesson, he wouldn't stop. The next night at home he quit doing it after about 20 minutes, Today we tried draw reins and lots of serpentines and figure eights. He got better, which still makes me think because he has to concentrate on what hes being asked, he forgets temporarily to do "his thing", for about once around the ring. He's five, beautiful mover, lovely attitude, kind eye, Warmblood/ Thor. cross.

We're borrowing a KK bit that is rather fat. He really did not like a full cheek snaffle (unruly). Any more ideas? We have a Pony Club mounted tomorrow, so this should prove interesting with other horses in the ring.

There are several reasons why horses shake their heads. It can be resistance, a condition called photic head shaking, ill fitting tack, ear problems (ticks, mites, fungus), or even cervical subluxations.

In my experience with horses I find them to be very compliant as a rule and barring an obvious miscommunication or the asking for an action the horse is unable to perform, for the most part they will usually do what you ask. Since the horse stands quietly until mounted, I would tend to look elsewhere for the problem.

My guess would be photic head shaking.

The condition called photic head shaking is said to be caused by an allergy to sunlight. John E. Madigan, DVM, MS, Diplomate ACVIM, Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis who is one of the foremost researchers in this area offers the following...

"Headshaking in horses has been observed by horsemen and veterinarians for nearly 100 years. Several causes have been suggested, including middle ear disorders, ear mites, cranial nerve disorder, guttural pouch mycosis, and vasomotor rhinitis. But treatment has had little effect on this problem. In a study recently conducted at the University of California, Davis, it was discovered that headshaking was the result of a pathophysiologic mechanism similar to the photic sneeze in humans. Optic-trigeminal summation was suggested as the means by which the horse develops facial neuropathic pain in response to light stimulation.

This condition is characterized by shaking of the head side to side, up and down, acting like a bee has gone up the nose, snorting or sneezing with headshaking, and rubbing the nose on objects or on the ground while moving. The most common onset of headshaking is in spring and early summer when sunlight becomes more intense. These symptoms are usually enhanced when the horse is worked or exposed to direct sunlight. Outdoor behavior of horses which suffer from this condition suggests that the horses seek to diminish their exposure to sunlight naturally. For example, the horse will seek shady areas, or the horse may put his face right under the tail of other horses, such as following the horse in front of him on a trial ride so closely that his face is under the leader's tail.

It is thought that stress created by sunlight and exercise may trigger a response of the central nervous system that causes the headshaking response in affected horses. With these stimuli, the horse experiences a tingling sensation or inappropriate stimulation of the sensory branches of the trigeminal nerve in the muzzle area. It is also thought that alterations in blood flow could explain the sudden nasal rubbing, snorting, and flipping of the nose. The pain felt by the horse is referred to as neuropathic pain, and may be persistent or intermittent.

Also of note is that in humans it is thought that a central sensitization process following certain peripheral injuries can lead to central nervous system changes that permanently alter pain perception and thresholds, and this may hold true for equines as well.

Headshaking can manifest itself in all breeds and disciplines equally because it has a physiological basis and it can cause headaches for owners or riders. Horses which exhibit headshaking syndrome become unruly or even dangerous when they are worked, many times with the blame falling on the rider. It previously was thought that perhaps the bridle was illfitting or the rider was too busy with his or her hands. But now there is evidence that it is not the rider at all, but rather a response to the burning and tingling sensations stimulated by stress in the horse.

While nothing can be pinned down as to exactly why some horses develop headshaking and others do not, it is thought that horses which have been exposed to the EHV-1 virus are more at risk. With this theory, the herpes virus lies dormant in the horse's trigemina ganglia, then with heat and stress created by either direct sunlight or intense exercise, the virus becomes active again, this time affecting the central nervous system and producing the symptoms characterized by headshaking. More studies need to be conducted to determine if EHV-1 has a connection with headshaking, but evidence now available is pointing in that direction.

Once your horse has been diagnosed with headshaking, there are a few options available as treatments. While there is no "cure all" when it comes to treating this condition, there has been some success with cyproheptidine therapy with or without environmental protection from sunlight, or light blocking eye protectors which have been shown to provide moderate to great improvement in three-quarters of the cases which headshake. Cyproheptidine, which is an anti-seratonergic, anti-cohligenic, and anti-histamine drug, works effectively in most horses inhibiting the normal activity in the trigeminal nerve.

Because headshaking is most commonly brought on by intense sunlight and exercise, the reduction of sunlight exposure usually helps reduce the symptoms. For example, many owners have found that if they work their horses at night, the symptoms are all but gone, but if they work their horse during the day, the symptoms appear within a few minutes and worsen the longer the horse is worked. The horse should also be kept in as dark an environment as possible. So in addition to treatment with cyproheptidine therapy, you should include environmental protection that shields the horse from as much direct sunlight as possible.

Additionally, headshaking tends to be a seasonal problem in most horses. It's usually the same time each year that the horse begins to exhibit headshaking symptoms. A horse might only headshake from March to August, or in severe cases, he might headshake year round. One of the reasons headshaking shows up seasonally is that seratonin and melatonin changes occur with the changes of the seasons."

The original of this quote appears at http://www.netpets.org/horses/healthspa/head.html

This is a condition that I have seen mostly in Warmbloods - Holsteiners, Trakes, Oldenburgers, etc and related crosses. It is a very perplexing problem.

The use of draw reins, serpentines, figure eights and other tricks seldom really correct anything and may cause your problem to worsen especially if it's stress related. Sepentines and figure eights are excellent limbering exercises, they really suck as vice correction methods.

Ill fitting tack should also be a fairly easy matter to resolve. One might do that by trying different headstalls and a variety of bits for the purpose of determining changes in tolerance only. I do not reccomend switching from bit to bit in hopes of stumbling across one he accepts. Bit changes have pretty deep effects and musical bits can cause you even more problems and confusion. If changing the bit changes the habit, THEN you can decide the best way to make the change permanent.

Quite some years ago I read an article about bits, their fitting and their action by Greg Darnell in Texas. It was a piece by someone who obviously understood bits and its logic was crystal clear to me. I do not remember whether he talked about English and Western uses or not. I lost the article and only recently came across his contact info.

My next bit problem is going to get tossed into the hands of Greg Darnell of
Greg Darnell Bits
Rt.2 Box 78-A-3
Lone Oak, Texas 75453
800-809-6131

As far as the matter of ticks, mites and fungal colonies in the ears that can usually be determined by a physical examination. Depending on the diagnosis, your vet will reccomend a suitable treatment.

At a clinic my business and horse partner, Kellie Sharpe, and I were conducting in New York I was demonstrating how a horse who is put through the Bonder (for a free copy of the procedure, send any email to my autoresponder, Bonder@MarvWalker.com ) allows you to stick your figures up its nose, in its mouth and into its ears and do pretty much anything else you want when the horse suddenly lowered its head to remove my finger and began severely shaking his head. The owner remarked that he had a bad habit of shaking his head while being ridden and at times made him unrideable.

Since it is almost unheard of for a horse to NOT allow me to do that after the bonder I persisted and was able to get my finger almost two inches into his ear when I felt a rock hard lump in the ear canal. I tried several times to get an idea what it was. I thought it was a very large tick, a stone or some other foreign object but the horse simply would not allow me to get near it to see what it actually was at the time.

While I was at it, I began examining the horse for another cause of headshaking, cervical vertebrae subluxations. I found several cervical vertebrae that were out of alingment and recommended the horse be examined by the equine chiropractor we were fortunate to have on the grounds.

Later I was told by the chiro that the horse had the worst case of axis rotation he had ever seen. The lump I felt bulging in the horse's ear was the horse's axis. When the subluxated axis, and its related atlas were pressed by the tack, headshaking occured.

The horse's axis is located just behind the jaw curve below the horse's ear. The distance between it and the horse's jaw should be the same on each side. Ideally, you would like the jaw and the axis to be at least a good finger width apart. If they are not, or are different, you'll have a horse that will have difficulty in coming onto the vertical and in making turns.

If your horse has a tight axis to jaw ratio or an obvious difference in the two sides, you'll need to have it seen by an equine chiropractor.