The effect of head size on the auditory brainstem response for two breeds of dog.

Many studies have shown that the auditory brainstem response (ABR) is influenced by the sex of the subject. The explanation offered most often for this sex difference is the smaller head size and brain dimensions in the female. Since breeds of dog have different head sizes, this makes them useful subjects to test the hypothesis that ABR latency covaries with head size. Subjects comprised 20 Dalmatians and 20 Jack Russell terriers. The maximum width of the head was 123 +/- 8 mm in the Dalmatian and 88 +/- 5 mm in the Jack Russell. An auditory brainstem response was carried out using a click stimulus at 75 dB nHL. The latency of wave V and the I-V interval was longer (0.3 and 0.17 ms respectively) in the Dalmatian, although the correlation of these measurements with head size (which ranged from -0.2 to +0.3) was not statistically significant. These findings do not support the theory that differences in ABR latency are due to differences in head size per se. Correlation of latency with body temperature and with age was also weak and not statistically significant.