PS3-20. Using Anogenital Distance from Birth to Weaning to Predict Puberty Attainment and Pregnancy by Artificial Insemination in Yearling Beef Heifers.

Abstract

Anogenital distance (the distance from the center of the anus to the top of the clitoris [AGD-C] or the dorsal commissure of the vulva [AGD-T]) is programmed during fetal life and associated negatively with pregnancy/AI in dairy heifers. We hypothesized that AGD-C and AGD-T are associated negatively with puberty attainment and pregnancy by artificial insemination (AI) in beef heifers. Heifers (n = 451) were submitted to AGD-C and AGD-T measurements at 2-4 months and 6-8 months of age. At the same timepoints, age, body weight, and hip height were recorded. When heifers were ∼14 months, were enrolled in the breeding season and submitted to an estrous synchronization protocol. On the day of the progesterone device (CIDR) insertion, heifers were submitted to transrectal palpation to attribute a reproductive tracts score (RTS;1-3 pre-pubertal and 4-5 pubertal), antral follicle count, and endometrial thickness. On the day of CIDR removal, heifers were fitted with an estrous detection patch (ESTROTECT™, Rockway Inc., USA) and the diameter of the largest follicle and presence of a corpus luteum (CL) was collected (n = 263). Heifers whose ESTROTECT had 50% or more rubbed off were considered in estrus. AI was based on estrous expression or timed AI, depending on the ranch, using the semen of 20 sires. Pregnancy/AI was measured 30-35 days after. Statistical analysis was performed using linear mixed-effects models and logistic regression from SAS. 84.9% (383/451) of heifers were pubertal at CIDR insertion, 52.9% (239/451) displayed estrus, and 32.2% (145/451) became pregnant/AI. At 2-4 months there was a tendency for a positive association of AGD-T and the follicular diameter (P = 0.089) and AGD-C and the probability of having a CL at CIDR removal (P = 0.0060). At 6-8 months, AGD-C was positively associated with age (P < 0.0001), body weight (P = 0.0109), hip-height (P < 0.0001), antral follicular count (P = 0.0224), uterine diameter score (P = 0.0019), RTS (P = 0.0022), and the probability of CL at CIDR insertion (P = 0.0075), while AGD-T was associated positively with age (P = 0.0037), hip height (P < 0.0001), uterine diameter score (P = 0.0179), RTS (P = 0.0211), and the probability of a CL at CIDR insertion (P = 0.0096). ROC curve analysis indicated that AGD-C and AGD-T at 2-4 and 6-8 months had a poor ability to predict puberty or pregnancy/AI (AUC < 0.70). In conclusion, our results were contrary to our proposed hypothesis. Our interpretation is that in beef cattle AGD might reflect the developmental status of the animal since it was positively associated with uterine ovarian measures related to fertility. Further, AGD may serve as an additional indicator of heifer developmental status, reflecting physiological maturity rather than directly predicting pregnancy/AI.