Endocrine Regulation of Reproductive Function in Dairy Cows

In addition to studying the paracrine regulation of early conceptus development, Dr. Ribeiro is also interested in understanding the endocrine regulation of reproductive function in dairy cows, as well as the use of blood biomarkers to assess reproductive and pregnancy health, and to inform management decisions. His studies with estrous synchronization programs, interferon-stimulated gene responses (ISGs), pregnancy associated glycoproteins (PAGs), bovine somatotropin (bST) and insulin-like growth factor-1 (IGF-1), steroid hormones, and anti-Müllerian hormone (AMH) provide good examples of this approach. For instance, he has shown in multiple studies that both ISGs and PAGs in peripheral blood during the peri-implantation period are reasonable predictors of pregnancy health status and its ability to survive to term.

Based on findings from a transcriptome investigation of conceptus cells during elongation, Dr. Ribeiro identified IGF-1 as a potential regulator of important changes in trophectoderm biology occurring during this process. Given that IGF-1 signaling might be deficient in lactating dairy cows due to metabolic factors, he tested the strategic supplementation of low doses of bST during the first 28 days after insemination to increase circulating levels of IGF-1 and, consequently, enhance its signaling in the gravid uterus, thereby improving conceptus development and survival. This treatment resulted in a 28% increase in pregnancy survival by the end of gestation. These results prompted discussions between pharmaceutical companies and regulatory agencies to extend the label of bST to reproduction purposes – a change that was successfully implemented in South America.

Serum AMH is an excellent biomarker for the size of the ovarian reserve (i.e. number of healthy follicles in the ovaries), repeatable within the same cow but highly variable among cows. Dr. Ribeiro’s investigation of serum AMH in 1,237 grazing cows subjected to a 100-d breeding season showed that lactation number, breed of the cow, and body condition score influence serum AMH concentrations. More importantly, he found no association between AMH concentrations and pregnancy at the first artificial insemination (AI) performed after synchronized ovulation. Additionally, AMH was negatively associated with detection of estrus on the day of timed AI. However, AMH concentrations was positively associated with pregnancy maintenance at the first AI and with pregnancy rate during the remainder of the breeding season following insemination after detection of spontaneous estrus. Based on these findings, he hypothesized that synchronization of ovulation used for first AI might have overridden the positive associations between AMH and fertility on the first breeding.