425 Award Talk: The importance of estrus expression and endometrial function for the pregnancy success in beef cattle.

Abstract In cattle, pregnancy success is partially limited by estrus expression, uterine function, and breed composition. Whole-animal and in vitro systems approaches were used to define the importance of such components to fertility. In objective 1, we validate artificial intelligence for estrus detection and prediction of pregnancy using accelerometers. Estrus (day 0; D0) of grazing beef cows (N=400) was detected by accelerometers and patches, cows received an embryo transfer (ET) on D7. Accelerometers had 90% accuracy in estrus detection but did not predict pregnancy/ET. The value of activity from the accelerometer was associated with follicular diameter (P=0.022) and estradiol concentrations (P=0.0032). For objective 2, 3, and 4 we associated endometrial biology in vitro with fertility outcomes in vivo of the respective cow. First, we validated a minimally invasive methodology (endometrial cytology; cytobrush) to harvest endometrial cells of live cows. Cells were 95% epithelial and responded to interferon-tau in culture. In objective 3 we used the cytobrush to characterize the existence of an endometrial memory associated with pregnancy outcome. Cows were submitted to pharmacological manipulations (progesterone and flunixin meglumine), cells were collected after the manipulation and studied in vitro by receiving an interferon-tau treatment. Progesterone or flunixin treatment in vivo in the cow affected the in vitro response to interferon-tau of the cells (P=0.003 and 0.0079 respectively). The retained in vitro response in the cells to the treatment in the cow was the evidence of an endometrial memory. For objective 4, 50 recipient cows received 8 consecutive rounds of ET on D7. On D4 cytobrush was performed and cells were cultured. Cows were classified as fertile, moderately fertile, and subfertile, according to how many rounds they remained pregnant. Cells from subfertile and moderately fertile cows had reduced probability of propagation in vitro (P=0.047). Thus, there are intrinsic repeatable characteristics in the cows that affect in vitro responses and fertility in vivo. Further, we studied reproductive biology of Brahman cows. In objective 5, we used the cytobrush on D4 to define the transcriptomic signature of the uterus after artificial insemination in Brahman cows. Anti-inflammatory responses and cholesterol biosynthesis were the pathways associated with pregnancy success. In objective 6, we studied conceptus-stimulated genes in blood cells of cows with different proportions of Brahman genetics. The expression of conceptus-stimulated genes increased with the proportion of Brahman genetics. In conclusion, accelerometers are reliable alternatives to detect estrus in beef operations. The success of the pregnancy is associated with estrus expression and endometrial function. Endometrial function is programmed by intrinsic and estrous cycle-specific influences in the cow, such as breed and the ability to remain pregnant consecutive times. Thus, an integration of individual characteristics and cyclic stimuli are needed for the pregnancy success in cattle.