Greater Reproductive Performance in Holstein Dairy Cows with Moderate Length of Anogenital Distance at First Service Postpartum

BACKGROUND: Previous studies have indicated negative association of anogenital distance (AGD) with fertility in dairy cows; however, the mechanism of inverse relationship is not completely understood. In this regard, postpartum uterine infections and their corresponding risk factors could diminish fertility of cows, yet there has been no research exploring the relationship between AGD and postpartum disorders. OBJECTIVES: The aim of this study was to investigate the relationship between AGD and postpartum reproductive performance in dairy cows. METHODS: AGD of Holstein dairy cows of a commercial dairy herd (n = 290) was measured at the first postpartum examination (days 28 to 32 postpartum) in millimeter. Cows were classified into three categories based on AGD length, including short anogenital distance (20% of cows with lowest values), intermediate anogenital distance (60% of cows with moderate values) and long AGD (20% of cows with highest values). Additionally, data of postpartum reproductive variables were retrieved form herd database. Dara were analysed using SAS software version 9.4.RESULTS: Rate of dystocia, twinning, retention of fetal membranes, puerperal metritis and clinical endometritis, calf birth weight and days to first service did not differ among the various AGD categories (P > 0.05). However, proportion of male offspring was lower in short AGD cows than intermediate and long AGD cows (P < 0.05). Furthermore, first service conception rate was greater in intermediate anogenital distance group than short and long anogenital distance groups (P < 0.05). CONCLUSIONS: In conclusion, the present study showed suboptimal first postpartum conception rate in cows with minimal and maximal length of anogenital distance and indicated that this inferior fertility was not mediated through alteration in rate of postpartum reproductive disorders.