An evaluation of equine headshaking syndrome and its management
Headshaking is a general term for a syndrome of behaviours that are exhibited by some
horses when they are exercised. These include sudden, intermittent shaking of the head,
excessive snorting and attempts to rub the nose. Examination by the veterinary surgeon
is often inconclusive (Lane and Mair 1987) although such horses may become
unrideable and, if severely affected, destroyed. Advances in our understanding of the
causes of the syndrome have been hampered by the absence of effective treatments and
a preponderance of case reports over controlled, epidemiological studies.
In this thesis, a range of epidemiological techniques were employed to answer questions
relating to the presentation, aetiology and treatment of the syndrome. A case-control
survey of 83 headshakers found no evidence to suggest that aspects of the management
of the horse were significant, general risk factors. Inferences from the reports of 200
horse owners regarding the presentation of the syndrome, the intermittency of its
appearance and association with trigger factors supported a proximate aetiology of nasal
irritation. A field trial of a bitless bridle and a light-limiting facemask suggested that
the presence of the bit or light alone are not significant triggers for British headshakers.
This is in contrast to reports from the USA, which, in the absence of evidence of any
difference in presentation of the syndrome, suggests that headshaking syndrome is the
final common pathway for irritation caused by a number of different factors.
An appropriate methodology for the assessmenot f the efficacy of alternative and
complementary therapies for headshaking was described using the principles of clinical
trials. The use of the horse-ownera s the assessoor f changei n the headshakings igns
was supported by a demonstration of the consistency of their reports. Two doubleblinded,
placebo-controlledc ross-overt rials, conducteda ccordingt o the methodology,
reported no evidence of any specific effect of an herbal supplement or a magnatherapy
headcollar. However, significant improvement was reported in the horses under both
placebo and verum conditions. This supports the assertion that control for the nonspecific
effects of treatment by placebo is essential if progress is to be made in
understanding the aetiology and treatment of headshaking.