PSIV-A-4 - Evaluation of the correlation between anogenital distance and other body size phenotypes in beef heifers

Abstract: The objective was to determine how anogenital distance (AGD) correlates to other body size phenotypic traits in beef heifers and if the relationships change from nine to twelve months of age. Reproductive success is one of the most important components in beef cattle production. The AGD is measured from the center of the rectum to the base of the clitoris. Shorter AGD has been associated with improved fertility in various species. Understanding the relationship between AGD and body size phenotypic traits is important for future breeding programs. Angus and Simmental ´ Angus heifers were weaned at 83±7 days of age (n = 121) or at 226±3 days of age (n = 9) and used in the analysis. After weaning, heifers rotationally grazed predominantly tall fescue pastures starting in April. Heifers were supplemented 1.36 kilograms of DDGS per heifer per day during the grazing season. Four monthly data collections took place from June to September, with heifers being 262±9 days of age at the time of the first collection. Phenotypes collected included heifer AGD, shoulder height, hip height, body length, and body weight. As the heifers were restrained in a squeeze chute with their tail held in an upright position, the AGD was measured using a digital caliper. Shoulder height was determined with a measuring stick from the withers to the base of the hoof, and hip height was determined from the hip bone to the base of the hoof. The body length was determined with a tape measure spanning from the point of the shoulder to the tail head. The association of AGD measurements and body size phenotypes were evaluated using the CORR procedure of SAS 9.4. Shoulder height was correlated to AGD (r ≥ 0.23; P ≤ 0.01) in 10-month-old and 11-month-old heifers but was not in 9-month-old and 12-month-old heifers (r ≤ 0.11; P ≥ 0.22). Hip height was correlated to AGD (r ≥ 0.17; P ≤ 0.05) in 10-month-old and 12-month-old heifers, but not in 9-month-old and 11-month-old heifers (r ≤ 0.11; P ≥ 0.21). Body length was correlated to AGD (r ≥ 0.19; P ≤ 0.03) in 11-month-old and 12-month-old heifers, but not in 9-month-old and 10-month-old heifers (r ≤ 0.10; P ≥ 0.24). Body weight tended to be correlated to AGD (r = 0.17; P = 0.06) in 9-month-old heifers, and was correlated to AGD in 10-month-old, 11-month-old, and 12-month-old heifers (r ≥ 0.21; P ≤ 0.01). In conclusion, anogenital distance is weakly correlated to body size phenotypic traits in beef heifers from nine to twelve months of age, with the most consistent relationships observed for body weight.