Effect of maternal heat stress at different stages of pregnancy on the reproductive performance and antral follicle count of the progeny of Holstein cows.

The objective was to evaluate the effect of maternal exposure to heat stress conditions at different stages of pregnancy on the reproductive performance and antral follicle count of progeny. The study was conducted at five commercial dairy farms located in southeastern Brazil. Retrospective data (2002 and 2015) on reproductive indices of daughters of Holstein cows that were exposed to heat stress conditions in the first (n = 447), second (n = 729) or third (n = 746) trimester of pregnancy and daughters of cows not exposed to heat stress (n = 359) were analyzed. Antral follicle count (AFC) and ovarian size were determined in a subgroup of animals (n = 242) by transrectal ultrasound. Statistical analysis was performed using the SAS GLIMMIX procedure. The number of services after first calving was lower in daughters of cows not exposed to heat stress conditions than in those exposed during different trimesters of pregnancy (P = 0.03). The calving interval was longer for daughters of cows exposed to heat stress conditions in the second and third trimesters of pregnancy than for those not exposed to heat stress (P = 0.01). In addition, the probability of pregnancy at first AI, (P = 0.01) and the AFC (P = 0.001) were greater in daughters of cows not exposed to heat stress conditions than in those exposed during the different phases of the gestational period. These findings indicate that maternal heat stress in different stages of pregnancy negatively affect the future fertility and AFC of bovine offspring.