Strategies to increase circulating progesterone in late metestrus and early diestrus in recipient dairy heifers and cows: A focus on induction of accessory corpus luteum formation.

Abstract

The capacity of recipients to support transferred embryos is a challenge for dairy cattle production systems. This review explores methods for increasing P4 to improve early pregnancy establishment in dairy cattle. A key aspect of P4 supplementation during the critical first weeks of pregnancy is its correlation with successful embryo elongation. Moreover, P4 was correlated to an increased chance of embryo survival after maternal recognition of pregnancy. Internal releasing devices increase circulating P4 concentrations but may negatively impact fertility possibly due to unwanted health pathologies such as vaginitis and the still undefined mechanism of haste luteolysis. The accessory corpus luteum (CL) induction in recipient dairy cattle increases endogenous P4 output increasing circulating P4 concentrations. Two ovulatory inducers are commonly used: gonadotropin-releasing hormone (GnRH) and human chorionic gonadotropin (hCG). Despite their distinct structures, GnRH and hCG are equally capable of inducing ovulation in cattle. The P4 supplementation by an accessory CL formation was widely used in fixed-time artificial insemination breeding programs, but still not exhaustively studied in embryo transfer (ET) programs. The induction of an accessory CL in ET programs has yielded inconsistent results depending on parity, embryo type production, embryo stage of development, and type of hormone used. Although maternal physiological mechanisms support the idea of increasing P4 for higher fertility and better embryo development, the actual results in creating a high-P4 maternal environment are still uncertain.