Preovulatory, postovulatory, and postmaternal recognition effects of concentrations of progesterone on embryonic survival in the cow

ABSTRACT Although fertilization rate usually is very high when male fertility is normal, pregnancy rates are below expectations when defined by the birth of live offspring in response to first service. Factors that affect establishment and retention of pregnancy include 1) preovulatory influences on the follicle and oocyte, 2) early postovulatory uterine and luteal function, 3) concentrations of hormones associated with trophoblastic and endometrial function during maternal recognition of pregnancy, and 4) less-well understood factors during the peri-attachment period. For example, decreased progesterone during preovulatory follicular development leads to a persistent follicle, premature resumption of meiosis, and a high incidence of embryonic death between the 2- and 16-cell stages. Elevated PGF_2α during d 4 to 9 of the estrous cycle not only caused luteolysis but also had a direct embryotoxic effect during the morula-to-blastocyst transition. Ideal conditions during placentation and attachment are not clearly defined. Late embryonic mortality might be increased after ovulation of persistent or immature follicles. Nominal increases in secretion of PGF_2α between d 30 and 35 might be important for attachment and placentation. Lower survival of embryos from wk 5 to wk 7 to 9 of gestation in the cow was associated with lower circulating concentrations of progesterone on wk 5. To maximize embryonic survival in the cow, management must provide high progesterone before estrus, quality detection of estrus, and timely insemination. Luteolytic influences of estradiol-17β or PGF_2α must be minimized early after mating and during maternal recognition of pregnancy, and high progesterone is needed during the late embryonic/early fetal period.

Key Words: Cows, Embryonic Survival, Pregnancy Rate, Progesterone

© 2004, by the American Society of Animal Science. All rights reserved.

J. Anim. Sci. 2004. 82(E. Suppl.):E24-E39

Implications

Both producers and researchers must be aware that the management required to maximize fertility in the cow is not simple. Very high fertility was observed in all animals in studies that involved frequent ultrasonographic scanning, careful observation of the cows, and breeding in relation to observed estrus. Based on these data, the continuing value of close observation for estrus in an artificial insemination program should be emphasized in educational programs. Treatments for synchronization of estrus must provide high progesterone, keep luteinizing hormone and estradiol low during treatment, and lead to development of a highly functional corpus luteum after mating. The reduction of luteolytic influences—such as excesses of prostaglandin F_2α or estradiol-17β early after mating, during maternal recognition of pregnancy, and during the late embryonic period—is important. Management systems designed to limit the metabolism of progesterone are needed during the estrous cycle before breeding as well as in these periods.