Auditory brainstem responses: How to assess hearing in horses

There is limited information about assessment of hearing in horses, although age, ototoxic drugs, disease and genetics all have the potential to affect hearing. Horses, like most animals, rely on hearing, although mild to moderate loss of hearing, particularly if unilateral, may not be detected by routine examination. Electrophysiological testing is therefore necessary to accurately detect and determine the extent of hearing loss in the horse. The Brainstem Auditory Evoked Response (BAER) uses a range of click stimuli to stimulate the auditory nerve, with this activity able to be measured via subdermal probes at three positions on the horse’s head. In this study, we examined 4 horses, aged 6, 6, 18 and 22 years, respectively, for clinical health and BAER response. The older horses showed partial deafness as evidenced by their increased BAER thresholds and wave V latencies. It was concluded that older horses can suffer from partial deafness as shown on BAER assessment. As a result, older horses may not respond as well to auditory signals and may compensate for any hearing loss with other senses.