A randomized double blind placebo-controlled clinical trial of Cetirizine in horses affected by seasonal headshaking

Headshaking is a threat to the welfare of affected horses.As seasonal headshaking may be triggered by allergic conditions, this clinical trial investigated whether the second-generation antihistamine cetirizine decreased headshaking.The objective was to assess the clinical effect of cetirizine versus placebo on seasonal headshaking.The hypothesis was that it would reduce headshaking by 50 % in 50 % of the horses.Thirty client-owned horses with seasonal headshaking were selected on the basis of information from the owner and a general clinical examination.In this crossover randomised double-blind placebo-controlled clinical trial, horses were given cetirizine (0.4 mg/kg twice daily PO for 7 days) or placebo (same number of tablets twice daily PO for 7 days) in a randomised order, with a washout period of 1 week in between.A 9-minute lunge protocol was recorded on video at the start and after both treatment weeks, and the number of headshakes in this 9-minute period was scored by two assessors in a blinded manner.Data of 29 horses were analysed.The number of headshakes decreased by more than 50 % in 10 horses when they were given cetirizine and in 8 horses when they were given placebo.This difference was not significant (p = 0.73).In a mixed linear model incorporating weather conditions no significant treatment effect was found either.In conclusion: no significant effect of cetirizine on seasonal headshaking was found in the group of horses included in this study.