South African Equine Veterinary Association Congress 2015 Protea Hotel Stellenbosch
imaging are required to detect such pathologies. It seems unlikely that these abnormalities alone
would lead to a 1% prevalence of head shaking amongst horses.
In humans with HTN “trigger zones” can often be identified. These are areas which when
stimulated, lead to pain. These can be anywhere within the trigeminal sensory field. Could this be
true for horses?
Many headshaking horses have factors which owners recognise to exacerbate the clinical signs.
These include changing season, exposure to light, exercise, rain and wind. It is possible that these
factors may cause or be associated with stimulation in an area that derives its sensation from the
trigeminal nerve.
The challenge remains, as to how to improve the welfare and rideability of these horses. There are
many options for the management of headshaking in horses. Unfortunately none of them are
reliably effective over a prolonged period of time. Reducing the horse‟s exposure to risk factors is
an important consideration. If symptoms are exacerbated by light, the horse could be ridden
indoors or wear an ultraviolet shaded mask. If the symptoms are exacerbated by increasing
exercise intensity, this could be avoided. Unfortunately many such measures are impractical and
would in fact prevent the horse from being used for its proposed purpose. Nose nets have become
a popular part of management for many head shakers. The mechanism by which these help is
unknown. Theories include minimising allergens, irritants and fast airflow from entering the nasal
passages, thus reducing stimulation in the nasal mucosa. Another theory is that the presence of a
constant stimulus down regulates the sensation from other areas in the trigeminal field. Neither of
these are confirmed.
Some horses will respond to medical management. No medication is licensed for headshaking in
horses and although some is available, none of the medications used have extensive
pharmacological or safety data available. Carbamazepine can be used at a dose of 2-8mg/kg orally
two to four times daily (ideally four). This drug may need to be administered tactically within two
hours prior to work. Unfortunately carbamazepine is often associated with signs of sedation.
Cyproheptadine may be given separately or in combination with carbamazepine and can also lead
to sedation. A dose of 0.3mg/kg orally twice daily can be used. A higher efficacy of treatment has
been reported for the two drugs combined than for either used alone. Increasing experience with
gabapentin is likely to lead to an increase in its use for the treatment of head shaking horses. A
recommended starting dose would be 5mg/kg orally twice daily. No side effects have been
reported at doses of up to 20mg/kg (only assessed after a single administration) and there are
published reports of a good effect in some patients. Unfortunately all three of the above
medications are prohibited substances, both under FEI rules and according to the NHRA.
Detection times are unknown, making the use of these drugs in competition horses difficult.
Surgical intervention can be used in the management of head shakers. Caudal compression of the
infraorbital nerve can be performed using platinum coils placed under fluoroscopic guidance.
This surgery has a 49% success rate, when judged up to eighteen months post operatively. It is
possible that some horses may deteriorate following surgical intervention. It is recommended that
surgery only be undertaken as a last resort, in cases where euthanasia is the only other option.
Infraorbital neurectomy is no longer recommended, due to its poor success rate combined with a
high rate of post-operative complications. The use of an infraorbital nerve block in the assessment
of headshaking is also not recommended. This is due t o the fact that it is neither sensitive nor
specific for trigeminal disease. Furthermore, it can lead to a severe exacerbation of headshaking
behaviour. In addition to this, the posterior ethmoidal nerve block is neither sensitive nor specific
for trigeminal disease and is associated with a number of potential complications, including
blindness. For these reasons it is also not recommended.
Initial working looking at the use of percutaneous electrical nerve stimulation (PENS) as a
management tool for equine idiopathic headshaking is encouraging. Following treatment a
significant improvement in clinical signs was observed in 85% of cases. Unfortunately using the
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