ENVIRONMENTAL-TEMPERATURE HAS AN INFLUENCE ON TIMING OF THE FIRST OVULATION OF SEASONAL ESTRUS IN THE MARE

A 10-yr retrospective analysis of the time of onset of seasonal ovulat ion derived from the records of a Thoroughbred horse stud at latitude 35 degrees S revealed a significant variation between years. The onset of seasonal ovulation was closely related to both the maximum (correl ation coefficient r=-0.56; P=0.09) and minimum (r=-0.67; P<0.01) envir onmental temperatures. The trend of the temperature rise and the level s attained in the weeks immediately prior to ovulation were similar fo r both the environmental maximum and minimum temperatures in all years of the study. Environmental temperature may therefore play an importa nt adjuvant zeitgeber for the timing of the first ovulation of estrus in the mare.