Can Repeated Exposure to Music Mitigate Horses' Reactions to Sudden and Unexpected Stimuli?

The living conditions imposed on horses mean that they are inevitably confronted with situations that can induce stress. Music is a promising tool for managing such situations, but its benefits could be attenuated by repeated exposure. In this study, we aim to determine whether music can mitigate horses' reactions to unexpected stimuli and if playing the same music daily leads to a loss of its efficiency. We compared three groups of 12 horses that were led on a route punctuated by potentially stressful stimuli for 10 consecutive days. Each group of individuals wore headphones and was consistently subjected to one of the three experimental conditions: a "music" test condition during which the same music track was played, a "noise" condition during which pink noise was played, and a "no-music" control condition. We found that music has a relaxing effect on horse behavior and heart rate. Interestingly, parameters with the pink noise were intermediate between the music and no-music conditions. Regarding the music's loss of efficiency through repeated playing, our results show that this tool continues to effectively mitigate the behavioral expression of stress after seven consecutive exposures, but this effect was not found every day. Music can therefore help make human-horse interactions safer by limiting the stress of horses faced with unexpected events, but further investigation is needed to understand the underlying mechanisms and ensure a safe and consistently efficient use in the field.