Differential effects of follicle-stimulating hormone dosage on in vitro embryo production in high- and low-anti-Müllerian hormone Holstein heifers

Female cattle with low-anti-Müllerian hormone (AMH) have fewer antral follicles and reduced in vitro embryo production (IVEP) potential than high-AMH females. In addition, granulosa cells of low-AMH females have a diminished responsiveness to FSH, despite elevated circulating FSH concentrations. However, AMH phenotype is generally not considered when establishing FSH dosage for ovarian superstimulation. Thus, this study aimed to assess the effect of FSH dosage on IVEP outcomes in high- and low-AMH female cattle. Pregnant Holstein heifers (∼50 d of gestation) with high (>331 pg/mL; n = 31) and low (<192 pg/mL; n = 31) circulating AMH were enrolled at 2 different locations for experiment 1 and experiment 2, respectively. Heifers were assigned to receive 0, 280, or 525 IU of FSH in a crossover design at 14 d intervals. Follicular wave emergence was synchronized using follicular ablation and FSH treatments, comprising 4 decreasing doses administered 12 h apart, were initiated 36 h after follicular ablation. Cumulus oocyte complexes (COC) were retrieved using ovum pick-up (OPU) 40 h after the last FSH administration and subjected to IVEP. Data were analyzed using generalized linear mixed models and orthogonal polynomial contrasts. In high-AMH heifers, total follicles and COC increased in a linear FSH dose-dependent manner. Similarly, blastocyst percentage increased linearly with increasing FSH dose, resulting in a linear increase in blastocyst yield (0 IU: 2.8 ± 0.4; 280 IU: 4.9 ± 0.7; 525 IU: 6.5 ± 0.8). In low-AMH heifers, there was a quadratic effect of FSH dose on total follicles, whereby there was a greater increase in number of follicles between 0 and 280 IU of FSH than between 280 and 525 IU. Conversely, the number of COC increased linearly with increasing FSH dose. There was a quadratic effect of FSH dose on blastocyst percentage, whereby the blastocyst percentage increased between 0 and 280 IU of FSH but not between 280 and 525 IU. Nevertheless, the number of blastocysts produced increased linearly with FSH dose (0 IU: 2.0 ± 0.4; 280 IU: 3.8 ± 0.6; 525 IU: 4.8 ± 0.8). In conclusion, the administration of FSH before OPU enhances IVEP in both high- and low-AMH heifers in a dose-dependent manner. Notably, the FSH-driven improvement in oocyte developmental competence reached a threshold at 280 IU of FSH in low- but not high-AMH heifers, suggesting that the optimal FSH dosage to maximize IVEP efficacy may be less for low- than high-AMH phenotype heifers.