Indicator traits of fertility in beef cows II: The role of progesterone in uterine biology and embryo development

Authors: Cushman, Robert - Bob

Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 4/18/2024
Publication Date: 4/18/2024
Citation: Cushman, R.A. 2024. Indicator traits of fertility in beef cows II: The role of progesterone in uterine biology and embryo development. In Proceedings: 1st Annual Reproduction Symposium, April 18-20,2024. Lavras, MG Brazil. Virtual.

Interpretive Summary:

Technical Abstract: Parameters of the estrous cycle influence fertility and fecundity in bovine females. Retrospective analyses of circulating concentrations of progesterone in the early luteal phase after determination of pregnancy status demonstrates a small but significant advantage for the future pregnant females. There is, however, negligible positive predictive value of a blood sample collected at day 4 to 6 after insemination to guarantee future pregnancy. In addition, there is little benefit to providing exogenous progesterone after insemination. This is due to an increase in shortened estrous cycles as the exogenous progesterone induces an early onset of luteolysis before a presumptive conceptus can signal its presence. Thus, it is critical to understand the biological variation in endogenous progesterone production and its relationship to fertility. Sub-fertile cows have decreased circulating concentrations of progesterone during the early luteal phase and diminished numbers of antral follicles. Numbers of antral follicles can be determined by ultrasonography and bovine females differing in follicle numbers can be used as a model to understand how these differences in progesterone concentrations influence histotroph composition, early embryonic development, and maternal recognition of pregnancy. While bovine females with increased numbers of antral follicles make better embryo donors in multiple ovulation embryo transfer (MOET) and ovum pick-up (OPU) protocols, the objective of embryo transfer is to propagate the best genetics for production traits such as milk production or weaning weight, not for superior ovarian phenotypes. If the increase in circulating concentrations of progesterone in bovine females with increased numbers of follicles does result in a superior uterine environment and more efficient mechanisms of recognition of pregnancy, then bovine females with increased numbers of follicles may also make better recipients for embryo transfer; however, it will require large numbers of recipients with ovarian phenotypes to determine if this is true. Understanding the relationships of components of the estrous cycle and improving the effectiveness with which we measure these components will allow us to apply reproductive technologies more efficiently, to select the best replacement heifers, and to make the timeliest decisions on when to cull a mature cow at the end of her productive lifetime.