Preliminary research using Equilume Light Masks provides hope for headshaking

Introduction:

Headshaking Syndrome (HS) is a poorly understood facial pain condition in horses that affects 1% of all equines, with the condition reported to affect geldings more often than mares. Symptoms include uncontrolled violent flicking of the head, snorting, rubbing the face on objects and legs and striking at the nose. Treatments and therapies for HS are limited, and often only partially successful.

More than 60% of owners report an onset or worsening of clinical signs in spring and summer, indicating that season plays an important role. When a veterinarian has ruled out all other common causes of headshaking behaviour, it is assumed that hypersensitivity of the trigeminal nerve, a large branched facial nerve, might be a cause. As the days lengthen in the spring, the light signal stimulates increased release of hormones from the brain that regulate reproduction in horses. This increase in firing of specific neurons is thought to somehow interact to make the trigeminal nerve more sensitive to environmental triggers. This increased sensitivity may result in worsening of headshaking behaviour in some affected horses (Pickles et al., 2011).

Normally, the release of testosterone from the testes in stallions acts to feedback and reduce the release of seasonal hormone release from the brain. It has been proposed that prolonged absence of this ability for negative feedback in geldings, who lack testes, may cause instability of the trigeminal nerve that somehow gives rise to neuropathic pain (Pickles et al., 2011). Previous attempts to block the seasonal hormone release by using drugs showed only limited or no success. The study reported here aimed to reduce the change in seasonal daylength signals using a blue light treatment that maintained exposure to the same daylength from autumn through to spring. This study was presented at the British Society for Animal Science conference in Galway, Ireland from 8^th-10^th April, 2025.

Materials and Methods:

Seventeen owners of HS horses were recruited via an online survey in Australia. Study eligibility was confined to owners of geldings with a history of moderate to severe headshaking behaviour, who had received a veterinary diagnosis of HS, and whose horses displayed seasonal onset of clinical signs during the spring/summer months. Each horse acted as their own control in a longitudinal study spanning 12 months. Horses were fitted with Equilume™ light masks that provided 15 h of blue light exposure from 08:00 to 23:00 daily for six months, starting at the autumn equinox (March 21^st in Australia). Participants were instructed to only remove the light masks for exercise, grooming and to charge weekly. In addition to the pre-study recruitment questionnaire (where details were collected on peak symptomology during spring/summer), questionnaires were circulated to collect information on HS clinical signs and intensity at the start (March/April), middle (June/July), and end-of-study period (October/November). Clinical signs evaluated were vertical ticking (flicking head towards chest); tossing head up and down; striking at head with front feet; rubbing face on objects/self and humans; and tightness of muzzle/mouth/lower lip. Clinical sign intensity was assessed on a 5-point scale: Not observed = 0; Very occasionally (i.e. observed once per week) = 1; Sometimes (i.e. observed several times per week) = 3; Often (observed at least once per day) = 4; Constantly = 5 (observed multiple times per day). The end-of-study questionnaire also asked owners to comment on perceived changes in their horse’s quality of life and assess overall changes in HS clinical sign intensity compared to the same period the previous year. Appropriate statistical tests were used to analyse results.

Results:

Of the 17 initial study participants, data from 10 who were fully compliant with providing survey responses, and whose horses met the study eligibility criteria were included in the data analysis. The number of reported HS clinical signs reduced over time (P = 0.02, Fig. 1A). There was no difference in the number of clinical signs reported between the pre-study period and the start of study (P > 0.05). A decrease in clinical signs from the pre-study period to the mid-study timepoint (P = 0.03) and from the pre-study period to the end-of-study period (P = 0.02, Fig. 1B) was observed. Statistical tests indicated a trend towards reduced clinical sign intensity scores for vertical ticking (P = 0.06), snorting (P = 0.05), head swinging (P = 0.07) and face rubbing (P = 0.08). ‘Striking at face’ was a clinical sign reported by two participants in the pre-study questionnaire, but was no longer observed at the mid- and end-of-study periods. Seven out of 10 participants reported a reduction in the overall severity of their horses’ clinical signs. Of these, two participants reported complete resolution of the condition in their horse. Finally, 6/10 participants reported improvements in quality of life.

Limitations of this preliminary study include the likelihood of observer bias, as owners knew that their horses were wearing a blue light mask and may have expected a positive effect. There was a small number of participants and there was no control group, so results must be interpreted cautiously.

Conclusions:

While results suggest that blue light treatment used to block the perception of shorter winter daylengths may offer a treatment option for managing HS clinical signs, further studies are warranted to support these findings. Future studies should comprise larger numbers of veterinary diagnosed headshaking horses and expert assessment of clinical signs before and after treatment from blinded observers.

Authors: Barbara A. Murphy^a; Rhea Kyriazopoulou^b; Camilla Mowbray^c

^aSchool of Agriculture and Food Science, University College Dublin, Belfield, Dublin 4,,Ireland

^bEquilume Ltd., Naas, Co. Kildare, W91 TP22, Ireland

^cIndependent Researcher, Galston, NSW 2159, Australia

Reference: Pickles, K.J., Berger, J., Davies, R., Roser, J., Madigan, J.E., 2011. Veterinary Record 168, 19.

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