1143 Plasma anti-Müllerian hormone in dairy heifers and associations with reproductive performance in two reproductive programs for first artificial insemination.

The objective was to investigate associations between plasma anti-Müllerian hormone (AMH) and reproductive performance in dairy heifers inseminated after detection of estrus or synchronized ovulation. Heifers (n = 601) in three farms were enrolled in the study 6 d before moving to the breeding pens. A randomized complete block design was used to assign one of two reproductive programs (RP) for first artificial insemination (AI): estrous detection (ED, n = 297) or timed AI (TAI, n = 304). Heifers in the ED group had their tailheads painted with chalk and were evaluated for signs of estrus once daily. Heifers receiving TAI were enrolled in the 5-d TAI protocol. On the day of enrollment, blood was sampled and analyzed for concentrations of AMH using an immune assay (AnshLite Bovine AMH CLIA). Within farm, concentrations of AMH in plasma were ranked and categorized as low (20% lowest values), high (20% highest values), or intermediate (60% intermediate values). Reproductive performance was evaluated for 84 d and the remaining AIs were performed after detection of estrus in both RP groups. Pregnancy was diagnosed on Days 32 and 60 after AI. Binary data were analyzed by logistic regression using the GLIMMIX procedure of SAS, and pregnancy rate was analyzed by the Cox's proportional hazard model using the PHREG procedure of SAS. Statistical models included the effects of AMH, RP, and their interaction, farm and semen. Concentration of AMH in plasma ranged from 2.6 to 566.3 pg/mL, and averaged 12.9, 30.9, and 85.4 pg/mL for low, intermediate and high AMH, respectively. Pregnancy per AI on Days 32 and 60 after first AI were not affected by AMH (d 32: 57.5, 65.9, and 64.2%, P = 0.21; d 60: 56.7, 62.6, and 58.3%, P = 0.38; for low, intermediate, and high AMH, respectively) or RP (d 32: 62.3, and 65.5%, P = 0.16; d 60: 58.2, and 62.8%, P = 0.11; for ED and TAI, respectively). Compared with low AMH, rate of pregnancy during the 84 d was similar for intermediate (AHR = 1.19, P = 0.12) and high AMH (AHR = 1.11, P = 0.46). Nonetheless, TAI had a faster rate of pregnancy (AHR = 1.58; P < 0.01) than ED. No interactions between AMH and RP were detected. In conclusion, plasma AMH was not associated with reproductive performance of dairy heifers in neither one of the two RP evaluated.