7 Relationships between antral follicle count, serum concentration of anti-Müllerian hormone, and fertility in dairy cows

In cattle, size of ovarian reserve can be estimated by means of antral follicle count (AFC) or peripheral anti-Müllerian hormone (AMH) concentration. Low AFC and low AMH concentration have been associated independently from each other with poor fertility. The aim of this study was to analyse the potential of a single AFC and AMH determination during postpartum period to predict subsequent fertility of dairy cows. For this purpose, 121 primiparous (31 ± 4 months), 112 biparous (45 ± 6 months), and 280 pluriparous (75 ± 22 months) cows were enrolled in the study. The cows belonged to four different breeds: Holstein Frisian (n = 241), Red Holstein (n = 128), Brown Swiss (n = 112) and others (n = 32, mostly Montbèliard, except for one Jersey and two crossbreeds) and had a predicted 305-day milk yield of 8359.1 ± 2260.9 kg. A single AFC determination was performed at 28 to 56 days after parturition by transrectal ultrasonographic evaluation. At the same time, blood was collected, and serum stored frozen (−20°C) until analysis for AMH, using a bovine AMH ELISA kit (A79765, AMH Gen II ELISA, Beckman Coulter). Cows were subjected either to AI or bred by bulls, and the number of inseminations and last date of breeding were recorded. Pregnancy diagnosis was performed using transrectal ultrasonography at least twice in every cow, on days 28–35 and days 50–70 after insemination, respectively. If cows were open for more than 200 days after parturition, they were classified as not pregnant. Based on number of antral follicles, cows were classified as having low (≤15 follicles, mean 10.5 ± 3.0, n = 246), intermediate (16–24 follicles, mean 19.3 ± 2.8, n = 202), or high (≥25 follicles, mean 28.7 ± 3.4, n = 65) AFC, respectively. Statistical analysis (SPSS version 27; IBM Corp.) was performed using nonparametric tests. Primiparous cows had lower AFC (P < 0.001) than biparous and pluriparous cows (13.6 ± 6.2 vs. 17.4 ± 6.9 vs. 17.0 ± 7.0). There was a strong interaction between parity and AFC group (P = 0.002), with a higher distribution of primiparous cows in the low AFC group (63.6% vs. 42.9% vs. 43.2%) and lower in the high AFC group (5.8% vs. 15.2% vs. 14.6%) than biparous and pluriparous cows, respectively. AFC was not affected by breed or by milk yield. In 204 (39.8%) cows, AMH concentration was below the detection limit of the assay (0.05 ng mL⁻¹), but it was not affected (P > 0.05) by parity. Cows with AMH concentration above detection limit had lower (P < 0.05) milk yield than those below detection limit (8177.2 ± 2334.4 kg vs. 8635.2 ± 2120.4 kg), but also a shorter (P < 0.05) calving to first service interval (84.0 ± 36.7 days vs. 93.8 ± 43.8 days) and a tendentially shorter (P = 0.07) calving to conception interval (122.4 ± 52.5 days vs. 131.3 ± 53.3 days). A moderate correlation (r = 0.34; P < 0.001) was observed between AMH concentration and AFC for cows with AMH above the detection limit. First-service conception rate (34.9%) and overall conception rate (67.4%) were not affected by AMH concentration or by AFC. Results of this study show that AMH concentration influences calving to first service interval and calving to conception interval, but also milk yield, suggesting its association with productivity in dairy cattle.