Photic headshaking in the horse: 7 cases.

The research article explores the occurrence of photic headshaking in horses, its potential triggers, and possible methods of intervention. The authors discovered that light might play a role in inducing this behavior and they were able to alleviate these symptoms with a number of methods, including eye coverings or darkness, as well as the use of certain drugs.

Research Methods and Case Description

• The research team studied a total of seven horses who were experiencing headshaking. Notably, they found no physical abnormalities in any of these horses.
• Six out of the seven horses first showed signs of headshaking during the springtime. This correlation led the researchers to believe that some external factor associated with this season may be contributing to the onset of these symptoms.
• To assess the potential role of light in triggering headshaking, researchers used blindfolds or dark grey lenses to block light from reaching the eyes. They also observed how the horses behaved in total darkness.
• In one unique case, the researchers found that a horse developed headshaking symptoms within two calendar weeks of the same date for three consecutive years. This spurred further investigation into any links between seasonality and headshaking.

Findings

• Light was found to play a crucial role in headshaking. When the horses’ eyes were blocked from light via blindfolding, they stopped headshaking. This occurred in five out of the five horses tested along these lines.
• Four out of four horses also ceased headshaking when placed in outdoor locations that were totally dark.
• Two out of three horses stopped showing symptoms when they wore dark grey lenses.
• These findings led the researchers to conclude that the horses’ outdoor behaviour was, in fact, an attempt to avoid exposure to light. This confirmed their hypothesis that light was a key factor in triggering their headshaking behavior.

Treatment and Conclusions

• Five out of seven horses improved upon treatment with cyproheptadine, a drug often used to treat certain types of allergies. The dosage used was 0.3 mg/kg of the horse’s body weight, administered twice daily.
• The researchers postulated that “neuropharmacological alterations associated with photoperiod mechanisms leading to optic trigeminal summation” could be the reason for the onset of headshaking during spring.
• A correlation between photic headshaking in horses and the photic sneeze reflex in humans was suggested, which indicates the possibility that these two phenomena could share an underlying mechanism.