Utilizing Body Temperature to Evaluate Ovulation in Mares

Although reproductive technology has added many dimensions to the horse breeding industry, less invasive and more efficient methods of evaluating follicular development and ovulation would be beneficial to both the commercial breeder and private horse owner. Because of the highly variable estrous cycle of the mare, it is difficult for breeders to coordinate insemination with ovulation, and much time is invested in evaluation via palpation, ultrasound, and teasing. In both dairy cattle and women, a significant change in body temperature has been measured during the hours immediately prior to ovulation. Research exploring the relationship of body temperature and ovulation in horses has been limited to one study in which no relationship between temperature and ovulation was identified. The current study utilized 38 mature mares and was conducted during the physiologic breeding season. Each mare was implanted in the nuchal ligament with a microchip capable of reporting body temperature, and rectal temperatures were obtained using a digital thermometer. Once an ovulatory follicle was detected using ultrasonography and the mare was exhibiting signs of estrus, the follicle size and temperature were recorded approximately every 6 h until ovulation. No difference was found in rectal temperature in relation to the presence or absence of a follicle. Under specific circumstances, temperatures obtained using the microchip were higher (P < 0.05) prior to ovulation compared with those temperatures collected immediately following ovulation.