Associations between anti-Müllerian hormone concentrations, morphometric traits, and reproductive performance in Holstein and Simmental heifers

The objective of this study was to assess the associations of age, live weight, withers height, anogenital distance (AGD), follicle diameter at artificial insemination, and anti-M & uuml;llerian hormone (AMH) concentrations with fertility outcomes in nulliparous Holstein and Simmental heifers. A total of 100 heifers were enrolled in the study and subjected to a progesterone-based 6day Co-Synch ovulation synchronization protocol, during which AGD measurements were obtained at protocol initiation and serum samples were collected for AMH analysis. Serum AMH concentrations were not associated with pregnancy outcome at first timed artificial insemination (TAI) (P > 0.05). However, heifers that conceived after two or fewer inseminations exhibited higher AMH concentrations compared with those requiring three or more inseminations (P < 0.05). In addition, AMH concentrations were significantly lower in infertile (P < 0.01) and repeat breeder syndrome (RBS) heifers (P < 0.001) compared with healthy fertile counterparts. No direct association was detected between AGD and fertility outcomes (P > 0.05). Holstein heifers exhibited significantly greater AGD and pre-insemination follicle diameter measurements than Simmental heifers (P < 0.001), whereas AMH concentrations did not differ between breeds (P > 0.05). The logistic regression model incorporating AMH, AGD, and breed demonstrated promising discriminative ability for identifying infertile (AUC = 0.871) and RBS heifers (AUC = 0.911) within this study population. Although neither marker alone reliably predicted firstservice conception, their combined evaluation may contribute to improved risk stratification under controlled herd conditions. However, given the limited sample size, these findings should be interpreted cautiously and require validation in larger populations.