The relationship between periovulatory endocrine and follicular activity on corpus luteum size, function, and subsequent embryo survival

The objectives of this study were to examine the relationships between periovulatory endocrine events, ovarian activity, and embryo survival after artificial insemination (AI) in cattle (Bos taurus). Eighty-four reproductively normal beef heifers were estrus synchronized using a prostaglandin-based regimen. Artificial insemination was performed between 5 and 21 h after heat onset. Ultrasonic examination of ovarian structures began 12 h after the onset of heat and continued every 6 h until confirmed ovulation. Blood samples were collected for measurement of estradiol, progesterone, and insulin-like growth factor-1 (IGF-1). Pregnancy diagnosis was conducted on Days 30 and 100 after AI. Embryo survival was defined as the presence of an embryo with a detectable heartbeat in a clear amniotic sac at Day 30 postinsemination. There was no effect of the intervals from the onset of heat to AI or ovulation or from AI to ovulation on embryo survival (P > 0.10). There was a tendency (P = 0.09) of an inverse relationship between preovulatory follicle size and embryo survival that was unrelated to concentrations of estradiol or IGF-1 during the periovulatory period (P > 0.05). There was evidence (P = 0.08) of a positive association between embryo survival and concentrations of progesterone on Day 7; however, this relationship was independent (P < 0.05) of hormonal and follicular measurements during the periovulatory period. This study shows that heifers could be inseminated up to 31.5 h before ovulation without compromising the probability of embryo survival. This study suggests that there is an optimum range of follicle size within which high embryo survival rates can be achieved.