PSI-13 Using anogenital distance at pre-breeding examination to predict pregnancy by artificial insemination in yearling beef heifers.

Abstract Approximately 50% of beef heifers do not become pregnant after artificial insemination (AI) which affects the profitability of beef operations. Anogenital distance (the vertical distance from the center of the anus to the top of the clitoris; AGD) is programmed during the fetal life and was associated negatively with pregnancy/AI in dairy heifers. We hypothesized that, yearling heifers with a shorter AGD during the pre-breeding examination have a greater probability of pregnancy/AI than heifers with a longer AGD. Heifers (n = 554) from 3 different farms, were submitted to an estrous synchronization protocol using an intravaginal progesterone device (CIDR; Eazi-Breed™ Cattle insert, Zoetis Animal Health, NJ, USA). At CIDR insertion, body weight and age were collected, heifers were submitted to transrectal palpation for reproductive tract score (ranging 1-5; 1-3 pre pubertal and 4-5 pubertal) and using a rice pelvimeter the pelvic area was calculated. Concomitant, AGD from the center of the anus to the top of the clitoris (AGD-C) and AGD from the center of the anus to the dorsal commissure of the vulva (AGD-T) were measured. Each farm used the following estrous synchronization protocol: Farm 1 (7-, 8-, or 9-day CIDR and AI), Farm 2 (14-day CIDR and timed-AI), and Farm 3 (7- or 8-day CIDR and timed-AI). On the day of CIDR withdraw heifers were fitted with an estrus patch (ESTROTECT™, Rockway Inc., USA), and the diameter of the largest follicle (n = 308) was measured. AI was performed using the semen of 5 bulls. Pregnancy/AI was measured 35 days after AI. Statistical analysis was performed using a linear mixed-effects model and logistic regression considering protocol as a block. 85% (471/554) of heifers were pubertal, 62% (344/554) displayed estrus, and 59% (167/283) were pregnant/AI. Pregnancy/AI on Farm 3 was 19.5% (53/271) and eliminated from statistical analysis. ADG-C and AGD-T were associated positively (P < 0.001, R2 = 0.1982). For each unit of increase in body weight, AGD-C increased 0.0064 units (P = 0.0003). AGD-C was associated positively with the probability of puberty during the pre-breeding examination (P = 0.0019) and probability of pregnancy in heifers without a corpus luteum (CL) at pre-breeding examination (Interaction AGD*CL P= 0.10). No association between pelvic area and follicular diameter with AGD-C or -T were observed (P > 0.05). ROC curve analysis found a poor area under the curve for both AGDs (AUC= 0.59) to predict pregnancy/AI. The association with AGD and reproductive measurements were contrary to our hypothesis and what is found in dairy heifers. Perhaps the prenatal effects on the AGD are diluted overtime and are not as influential to the reproductive outcome when the calf is an adult.