Predictive markers for superovulation response and embryo production in beef cattle managed in northwest Mexico are influenced by climate

Abstract

Important components of a successful embryo transfer program in cattle are the superovulatory response and embryo production. Anti-Müllerian hormone (AMH) and antral follicle count (AFC) have been proposed as biomarkers of the reproductive response in superovulated cattle; however, their predictive ability appears to be influenced by climate. Objective herein was to evaluate AMH and AFC as predictors of the number of ovarian follicles, corpora lutea, collected embryos and transferable embryos in cows managed in northwest Mexico under different climates. Multiparous Simmental beef donor cows were assigned in two experimental climatic groups, cool (January 15– May 14; n=66) and warm (May 15– September 14; n=62). All cows were given a superovulatory treatment, and then subjected to artificial insemination and non-surgical embryo collection. Transrectal ultrasonography was performed to determine AFC. Blood samples were collected to measure blood AMH concentrations. A mixed effects model was used to analyze superovulatory and embryo production responses in cattle including AMH, AFC and climate as fixed effects, age as covariate and herd as random effect. All fixed effects resulted as significant (P<0.05) sources of variation for the evaluated traits, and interactions between AMH/AFC with climate were observed but only for transferable embryos. Pearson correlations were calculated between AMH/AFC with superovulatory and embryo production variables for cool and warm experimental groups, and a regression analyses was performed to quantify these relationships. Cows with either AMH>400 pg/mL or intermediate to higher AFC increased (P<0.05) mean values for superovulatory and embryo production variables, suggesting both AMH and AFC as predictors. Climate also influenced cow responses as number of follicles, corpora lutea, as well as collected and transferable embryos increased 33, 38, 40 and 35%, respectively, during cool- (8-23 °C) compared to warm-climate (24-34 °C; P<0.05). Both AMH and AFC were moderately correlated with number of follicles, corpora lutea and collected embryos (P<0.05) and highly correlated with transferable embryos (P<0.01) during cool climate; conversely, these correlations were low (P>0.05) for donor cows managed in the warm months. Regression analyses suggested that total number of transferable embryos increased 0.005 per 1 pg/mL of AMH and improved 0.484 per 1 unit of AFC. In conclusion, superovulatory and embryo production responses in Simmental beef cows appear to be closely associated with AMH and AFC, which are proposed as predictors for transferable embryos; however, such relationships were only detectable in absence of heat stress.