Reduced embryo yield obtained from superstimulated ewes with low circulating AMH concentration is improved by lengthening the FSH treatment.

The aim of the present study was to evaluate: 1) the association between AMH, AFC, superovulatory response and embryo yield in sheep; and 2) the effect of FSH treatment length during superstimulation of the first follicular wave on ovarian response and embryo yield, particularly in ewes with low and high AMH. The experiment was performed on 63 Polled Dorset ewes that received an ovarian superstimulatory treatment during the first follicular wave (Day 0 protocol). Ewes were administered a total dose of 240 mg of FSH distributed in six (6-dose regimen, n = 30) or eight (8-dose regimen, n = 33) decreasing doses administered 12 h apart. On Day -9 (random stage of the estrous cycle) and Day 0 (day of the first FSH dose) ovarian ultrasonography was performed and blood samples were collected for AFC and AMH determinations, respectively. A weak positive correlation between AMH and small AFC (follicles <4 mm) was observed (r = 0.23; P = 0.07), and AMH concentration was positively correlated (r = 0.29; P < 0.05) with the number of corpora lutea (CL) determined at embryo collection (i.e., 6 d after insemination). The length of FSH treatment tended (P = 0.06) to affect the ovarian response, such that the number of CL was greater in 8-dose than 6-dose treated ewes, while no differences (P > 0.10) in embryo yield outcomes were observed. For further analysis, ewes were classified into low (<7 ng/mL) and high (>10 ng/mL) serum AMH. In high AMH ewes, there were no differences (P > 0.05) in the number of CL nor embryo yield between the 6-dose and 8-dose treatment (e.g., 7.8 ± 2.4 and 8.3 ± 2.5 transferable embryos, respectively; P = 0.92). Conversely, for low AMH ewes, fertilized ova and embryo yield were greater (P ≤ 0.05) for ewes receiving the 8-dose than the 6-dose superstimulatory treatment (e.g., 8.4 ± 2.8 vs. 2.7 ± 0.9 transferable embryos, respectively, P ≤ 0.05). In conclusion, embryo production in poor responding ewes with low low circulating AMH is improved by extending the superstimulatory treatment length from 6 to 8 FSH doses.