Reproductive physiological outcomes of dairy cows with different genomic merit for fertility: Biomarkers, uterine health, endocrine status, estrus features, and response to ovarian synchronization.

Our overarching objective was to characterize associations between genomic merit for fertility and the reproductive function of lactating dairy cows in a prospective cohort study. In this manuscript, we present results of the association between genomic merit for fertility and indicators of metabolic status and inflammation, uterine health, endocrine status, response to synchronization, and estrous behavior in dairy cows. Lactating Holstein cows entering their first (n = 82) or second (n = 37) lactation were enrolled at parturition and fitted with an ear-attached sensor for automated detection of estrus. Ear-notch tissue samples were collected from all cows and submitted for genotyping using a commercial genomic test. Based on genomic PTA values for daughter pregnancy rate (gDPR), cows were classified into a high (Hi-Fert; gDPR >0.6; n = 36), medium (Med-Fert; gDPR -1.3 to 0.6; n = 45), or low (Lo-Fert; gDPR <-1.3; n = 38) group. At 33 to 39 DIM, cohorts of cows were enrolled in the Presynch-Ovsynch protocol for synchronization of estrus and ovulation. Body weights, BCS, and uterine health measurements (i.e., vaginal discharge, uterine cytology) were collected from parturition to 60 DIM, and milk yield was collected through 90 DIM. Blood samples were collected weekly through 3 wk of lactation for analysis of BHB, nonesterified fatty acids (NEFA), and haptoglobin plasma concentrations. Body weight, BCS, NEFA, BHB, and haptoglobin were not associated with fertility groups from 1 to 9 wk after parturition. The proportion of cows classified as having endometritis at 33 to 36 DIM tended to be greater for the Lo-Fert than the Hi-Fert group. The proportion of cows that resumed cyclicity did not differ at any time point evaluated, and there were no significant associations between probability or duration and intensity of estrus with fertility group. Cows of superior genetic merit for fertility were more likely to ovulate, have a functional corpus luteum, have greater circulating progesterone, and have larger ovulatory size than cows of inferior fertility potential at key time points during synchronization of estrus and ovulation. Despite observing numerical differences with potential performance consequences for the proportion of cows that responded to synchronization of ovulation and were both cyclic and responded to the Ovsynch portion of the synchronization protocol, we did not observe significant differences between fertility groups. Although not consistent and modest in magnitude, the collective physiological and endocrine differences observed suggested that cows of superior genetic fertility potential might have improved reproductive performance, at least in part, because of modestly improved endocrine status, uterine health, and ability to ovulate.