The effect of ocular blinkers on the horses' reactions to four different visual and audible stimuli: results of a crossover trial.

OBJECTIVE To determine the effect of ocular blinkers on driving horses' reactions to visual and audible stimuli. DESIGN Balanced crossover trial with horses randomly assigned to either wear blinkers or not wear blinkers first or second, then subjected to repeated sequences of four distinct stimuli (chain rattle, cap gun, umbrella opening, and shaking of an aluminum can containing coins). Two weeks later, this process was repeated with the ordering of wearing blinkers reversed. ANIMAL STUDIED Eight driving horses of various breeds. PROCEDURES Responses were recorded quantitatively as inter-beat times (the time between each heart beat in msec) and qualitatively via video recording. Statistical analysis of the first 10 s of inter-beat times poststimulus assessed the effect of the presence of blinkers, order of blinker application and stimulus type using a linear regression model with a random effect for horse. RESULTS Wearing blinkers is significantly associated with a decrease in the inter-beat times (increase in heart rate) when they are worn by horses experiencing an unfamiliar sound. However, wearing blinkers is significantly associated with an increase in the inter-beat times (decrease in heart rate) when worn by horses experiencing a primarily visual, familiar stimulus. CONCLUSIONS AND CLINICAL RELEVANCE Trained driving horses, when they wear blinkers, have a decrease in inter-beat time (an increase in heart rate) when there is an unfamiliar sound. This may have relevance to horses who have limited vision caused by trauma or disease.