Anogenital Distances Measurements Predict Heifer Reproductive Longevity and Success in Pubertal Classifications

A heifer's ability to attain puberty early and maintain estrous cyclicity is predictive of greater reproductive longevity. Our laboratory has identified 5 pubertal classifications from weekly blood collections collected between weaning to breeding (Oct to May). These five pubertal classifications are:1) Early, 2) Typical, 3) Start-Stop-Start (SSS), 4) Start-Stop-Discontinuous (SSD), and 5) Non-Cycling (delayed puberty) with Early and Typical heifers initiating and maintaining cyclicity during the collection period. Non-Cycling and SSD heifers had the fewest calves from artificial insemination in the first 21 days of calving and were the most sexually immature based on their reproductive tract scores. Heritability of pubertal classifications was moderate (0.36), and those that initiated and maintained cyclicity (Early + Typical) vs those that did not initiate or maintain cyclicity (Non-Cycling + SSD) were highly heritable (0.59). Both anogenital distance to vulva (AGDv) and AGDc (center of anus to base of clitoris) and the ratio of the two measures (AGDv/AGDc) in heifers have been associated with reproductive performance. Longer AGDv in rodents has been associated with androgen exposure during gestation resulting in reduced fertility. Our hypothesis was that AGDV, AGDC, or their ratio is associated with specific pubertal classifications, allowing for predictions of their reproductive efficiency and lifespan. Prior to breeding (May of each year), AGD data were collected from 337 heifers in the physiology herd born in 2020-2023. R-Studio was utilized for two one-way ANOVA analysis while a TUKEY determined associations between AGDv, AGDc, and AGDv/AGDc with our 5 pubertal classifications and the comparison of Typical + Early vs Non-Cycling + SSD. Non-Cycling heifers AGDv (45.51±1.0; n = 64) was longer than Early (41.98±0.87;n=82; p < 0.05) and Non-Cycling + SSD (45.31±0.88; n = 84) had longer AGDv than Early + Typical (43.14±0.52; n = 147; p < 0.05) indicating that the females with delayed puberty or irregular cyclicity may have reduced reproductive longevity, perhaps due to gestational exposure to androgens. Additionally, Non-Cycling (104.65±1.36; p < 0.01), SSS (105.65±1.56; p < 0.01) and Typical (105.89±0.89; p < 0.001) ADGc were shorter than Early (111.15±1.18; p < 0.01) suggesting that Early heifers may have more mature external genitalia with the potential for enhanced future reproductive performance success. Early heifer reproductive longevity was further reinforced by the Non-Cycling (43.98 ±1.08; p < 0.001) and Typical (41.17±0.71; p < 0.001) heifers having longer AGDv/AGDc ratios compared to Early (37.59±0.93; p < 0.001). Overall, these AGD measurements in our heifers demonstrate that Non-Cycling (delayed puberty) classification had the least favorable AGD measurements indicating increased androgen exposure during gestation resulting in reduced future fertility. In contrast, Early heifers have AGD measurements that are more favorable for reproductive performance and longevity. Thus, AGD measurements may allow producers to use this non-invasive measurement to select for females to retain in the herd increasing their operations profitability.