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The Brainstem Auditory Evoked Response (BAER) is the gold standard for testing the auditory system in many animals, including canines. The procedure involves measuring electrical responses that occur at various locations along the auditory pathway and brainstem. Electrical activity occurs as a result of auditory stimulation, presented either via air conduction or bone conduction, and can be measured via small subdermal electrodes. Since this method measures a physiological response to sound, a behavioral response from the animal is not required, resulting in an objective assessment of that animal’s auditory function. Previous studies have been conducted, namely Kemper et al. (2013), in which the effect of head size on the air-conducted BAER in dogs was examined. It was found that there was no significant difference on the response waveform between various head sizes. Munro, Paul, et al. (1997) conducted a study to establish normative data for bone conduction BAER waveforms in dogs. They reported a consistent observable difference in Wave latency between the two breeds tested, one small breed and one large breed. The purpose of the following study was to further investigate how head size affects the waveform of a bone conduction BAER in dogs, following the findings of Munro, Paul, et al. (1997) and Kemper et al. (2013). The following research questions were investigated: What effect does head size have on the absolute latency of Wave V for bone conduction BAER testing in canines? Does the average amplitude of Wave V of a bone-conducted brainstem auditory evoked response (BAER) differs between the two test groups? It was hypothesized that there would be a positive correlation between head size and Wave V latency and that no significant difference would be found between the amplitude of Wave V of small dogs and of large dogs.

Data were collected and analyzed from twenty dogs: ten small dogs and ten large dogs. Head size was calculated using two measurements taken using a caliper. An air conduction BAER screening was performed on each dog prior to testing to confirm normal auditory status. Bone conduction BAER waveforms were obtained and replicated for each subject. Absolute peak latencies and peak-to-trough amplitudes were analyzed for Wave V for each subject. There was an observable difference in Wave V latencies between the groups, but it was not found to be statistically significant when a Mann-Whitney U-test was performed. A positive correlation (r = 0.4929) was found between head size and Wave V latency. A difference between the average Wave V amplitudes for each group was observed. This difference was found to be statistically significant along with a negative correlation (r = -0.5789) between head size and Wave V amplitude. It was hypothesized that these findings relate to the differences in anatomical dimensions; a longer auditory pathway from the cochlea to the brainstem would therefore result in longer transmission times of the electrical signal, manifesting in longer peak latencies of Wave V. Similarly, smaller anatomical dimensions result in the recording electrodes to be closer in proximity to the source of the electrical potential in the brainstem. It was suspected that this is responsible for the differences seen in Wave V amplitude, as the voltage of the electrical potential decreased with increased distance between the source and recording electrode (Atcherson & Stoody, 2012). Future studies should be conducted with larger sample sizes to replicate and further validate these findings.