209 Ovarian stimulation with FSH in low AMH heifers increases ovarian response and oocyte developmental competence in a dose-limited manner

Cattle with lesser circulating anti-Müllerian hormone (AMH) concentrations present reduced antral follicle population, which in turn leads to reduced embryo yield after in vitro embryo production. In addition, circulating FSH is chronically elevated in low AMH cattle and their granulosa cells have diminished responsiveness to FSH stimulation. The aim of this study was to evaluate the effect of FSH dose on ovarian response and in vitro embryo production in low AMH heifers. Pregnant Holstein heifers had a blood sample collected at 46.9 ± 4.7 days of gestation, and heifers with circulating AMH concentrations in the lowest 25% of the population (<192 pg mL⁻¹) were selected and enrolled in the study. Heifers (n = 31) were randomly assigned to receive either 0 mg (FSH0), 160 mg (FSH160), or 300 mg (FSH300) of porcine FSH (Folltropin, Vetoquinol-USA) in a crossover design. Heifers were subjected to ovum pickup (OPU) at 51.9 ± 4.7, 65.9 ± 4.7, and 80.0 ± 4.8 days of gestation with a 14-day “washout” between OPU sessions. Before each OPU session, follicle ablation (d 0) was performed to synchronize follicular wave emergence, and FSH administration (four decreasing dose injections 12 h apart) was initiated 36 h later (Day 1.5). OPU was performed ~40 h after the last FSH administration (Day 5), and cumulus–oocyte complexes (COCs) were subjected to in vitro embryo production using standard procedures. Follicle numbers and size distribution were determined on Day 5 using B-mode ultrasonography. Differences between treatment groups were evaluated using generalized linear mixed models and orthogonal polynomial contrasts. There was a quadratic effect (P ≤ 0.05) of treatment on the total number of follicles at OPU and the proportion of medium (6–10 mm) and large (>10 mm) sized follicles. The total number of follicles and the percentage of medium and large-sized follicles increased as FSH dose increased; however, this increase was greater between 0 and 160 mg than between 160 and 300 mg. The total number of COCs and the number of viable COCs increased linearly (P < 0.0001) with increasing FSH dose. Although the number of blastocysts produced per heifer increased linearly (P < 0.0001) with increasing FSH (FSH0, 1.9 ± 0.4; FSH160, 3.8 ± 0.6; FSH300, 4.8 ± 0.8), a quadratic effect (P = 0.05) was observed for blastocyst rate. Increasing the FSH dose from 0 mg (48.4 ± 5.2%) to 160 mg (64.3 ± 4.1%) increased the blastocyst rate; however, increasing FSH dose from 160 to 300 mg (61.5 ± 4.0%) had no effect on blastocyst rate. Furthermore, there was a tendency (P = 0.07) for a quadratic effect on the proportion of heifers producing two or more blastocysts, following a similar pattern as described for blastocyst rate. In conclusion, the use of FSH before OPU in low AMH heifers increases superstimulatory response and oocyte developmental competence. However, these effects appear to be dose-limited, with greater improvements observed from 0 to 160 mg than from 160 to 300 mg of FSH. Collectively, these results suggest that moderate FSH doses might be preferable during ovarian superstimulation for in vitro embryo production in low AMH cattle.