Researchers in Ireland and UK are undertaking further research into a potential treatment for headshaking syndrome in horses.
The use of Equilume masks to treat headshaking in horses in Australia has shown positive results, according to a recent preliminary study led by Associate Professor Barbara Anne Murphy, the Head of Equine Science within the School of Agriculture and Food Science at University College Dublin.
The commercial availability of a blue light mask that administers extended day length via a headpiece to horses from Equilume has proved successful at manipulating seasonal reproductive activity through its suppression of melatonin in horses.
While the causes of Equine Headshaking Syndrome are not fully understood, one hypothesis is that the increased release of gonadotropin-releasing hormone from the brain in the spring and summer affects the sensitivity of the trigeminal nerve which runs along the horse’s face.
Previous studies investigating treatments for headshaking have tried to alter the release of this hormone through vaccination or the administration of melatonin, but without success.
More research is now needed to validate these findings in a larger cohort of horses and with additional specialised expertise.
To that end, a new collaboration between veterinary researchers in Ireland and the UK has been established with the team currently recruiting horses to research further the use of blue light therapy to treat Equine Headshaking Syndrome.
That research team is led by Prof Murphy, in close collaboration with Drs. Veronica Roberts (University of Bristol), Kirstie Pickles (equine internal medicine consultant and researcher), Clodagh Kearney (UCD School of Veterinary Medicine) and David Marlin (AnimalWeb Ltd).
Read more about this new study and how to participate in our separate article here.
What is headshaking syndrome?
Whilst it’s normal for a horse to shake its head some of the time, 4.5% of the UK equine population shake their heads more than is normal. There are many causes of headshaking, but most horses are affected by trigeminal-mediated headshaking. This is a neuropathic facial pain syndrome, characterised by spontaneous, involuntary, violent flicking of the head, snorting, rubbing the face on legs or objects and striking at the nose with a forelimb.
Signs tend to worsen under specific environmental conditions such as exposure to heat, bright light, wind, high pollen count and when horses are exercised. Affected horses may exhibit mild to severe signs and symptoms that impact welfare and horse-owner interactions. Horses and ponies of any breed may be affected; however, it may be more prevalent in geldings. Therapeutic options are limited, and treatments are only partially successful.
How does trigeminal-mediated headshaking affect equines?
Trigeminal-mediated headshaking appears to be an acquired disorder, and its pathophysiology is unclear. The prevalent theory is that pathways implicating the trigeminal nerve play a role in the expression of the syndrome. The infra-orbital branch appears to be sensitised in affected horses, firing at a much lower threshold than normal. There appears to be functional but not structural changes to the nerve. Horses are long-day breeders, and photoperiod-driven increases in gonadotropin-releasing hormone (GnRH) from the hypothalamus regulate the release of gonadotropins that stimulate spring reproductive behaviour in horses.
In some studies, geldings are more likely than mares to be affected by TGM headshaking. Some trigeminal-mediated headshakers are only, or worse, affected in the spring and summer. Geldings might be predisposed to trigeminally mediated headshaking as they are unable to regulate springtime GnRH release, which occurs via negative feedback of testosterone produced by the testes. This could potentially lead to sensitisation of the trigeminal nerve and the development of neuropathic pain. However, there may be more than one cause with the same clinical manifestation, which may also justify the variable response rates to treatment and lack of an overall effective treatment option.
Affected horses suffering trigeminal-mediated headshaking are considered to have neuropathic facial pain, which negatively impacts welfare and quality of life. The degree of this negative impact is assumed to correlate with the severity of pain, currently explored by evaluating clinical sign frequency and severity.
As treatment options available only partially resolve symptoms, owners often seek euthanasia as a means of providing relief to their horses. The number of treatment options reported used by horse owners to manage this syndrome, and their perceived lack of efficacy demonstrate the importance of continuing to investigate alternative therapy.
Participate in the new study
If you own or manage a horse or pony with headshaking symptoms, and you would like to participate in this important research into blue light therapy, please complete the recruitment survey here: https://www.surveymonkey.com/r/Headshaking_recruit
