Comparative analysis of vocalizations of thoroughbred mares (Equus caballus) between estrus and diestrus.

We investigated the differences between vocalizations of mares in estrus and diestrus and determined the spectrographic parameters to discriminate estrus from diestrus. Thoroughbred brood mares (n=89) were exposed to a teasing procedure for 3 min, and we recorded all vocalizations emitted from them. Among the mares, 56.5% of estrus and 78.6% of diestrus mares emitted calls toward an approaching stallion, indicating that there was higher tendency in the occurrence rate of vocal responses in diestrus than estrus mares. We analyzed the spectrographic data of the mares (25 estrus and 22 diestrus mares) emitting calls in the form of a squeal toward an approaching stallion. Based on broad bandwidth spectrographic analysis, the duration and third formant of the call have a significant effect on discriminating estrus from diestrus.