ABSTRACT

Bovine Estrous Cycle Endocrine parameters during the four primary phases of the 21 day bovine estrus cycle, proestrus (day 19 to onset of estrus), estrus (day 0), metestrus (days 1 to 4), and diestrus (days 5 to 18), show cyclic changes (Part A), similar to those of other ruminants, with control exerted by the hypothalamic-pituitary axis in concert with cyclic ovarian structures and the uterus. Cows exhibit a short period of sexual receptivity (estrus), about 18 hours, with ovulation occurring less than a day later. The duration of estrus in heifers is shorter, about 15 hours.