Repeatability of antral follicle counts and anti-Müllerian hormone and their associations determined at an unknown stage of follicular growth and an expected day of follicular wave emergence in dairy cows

•Antral follicle count is less repeatable between unknown and known stages of follicular growth.•Anti-Müllerian hormone is highly repeatable between unknown and known stages of follicular growth.•Antral follicle count and anti-Müllerian hormone are moderately correlated in dairy cows.

The objectives were to determine (1) the repeatability of antral follicle counts (AFC) and anti-Müllerian hormone (AMH) concentrations at an unknown stage of follicular growth (FG) and at an expected day of follicular wave emergence (FWE) in dairy cows, and (2) the association between AFC and AMH at the above two stages. Transrectal ultrasound imaging of the ovaries and blood sample collection were performed on 91 lactating Holstein cows (33 primiparous, 58 multiparous) to determine AFC and serum concentrations of AMH at an unknown stage of FG (mean ± SEM; 14 ± 0.5 d postpartum) and an expected day of FWE (mean ± SEM; 73 ± 0.5 d postpartum, approximately 36 h after the 2nd GnRH of Ovsynch protocol). The AFC ranged from 10 to 53 (mean ± SEM; 26.1 ± 1.0) and 6 to 45 (mean ± SEM; 23.4 ± 1.0) at an unknown stage of FG and expected day of FWE, respectively (P = 0.02). Serum concentrations (pg/mL) of AMH ranged from 13.9 to 528.8 (mean ± SEM; 187.3 ± 13.1) and 38.2 to 774.1 (mean ± SEM; 218.7 ± 14.5) at an unknown stage of FG and expected day of FWE, respectively (P < 0.01). The repeatability estimates for AFC and serum AMH concentrations between an unknown stage of FG and the expected day of FWE were 0.37 and 0.73 (P < 0.01), respectively. The correlation between AFC and AMH was moderate at an unknown stage of FG (r = 0.54; P < 0.01) and at an expected day of FWE (r = 0.59; P < 0.01). In summary, both AFC and AMH were repeatable when measured at an unknown stage of FG and an expected day of FWE, but the repeatability was greater for AMH. Thus, if cows are tested at an unknown stage of FG, serum AMH may be a more reliable phenotype than AFC to test association with reproductive outcomes. Furthermore, AFC and AMH were moderately correlated at the two stages examined.