Effects of season and superovulatory treatment on embryo yields in fine-wool Merinos maintained under field conditions.

The aim of the study was to assess the effects of superovulatory treatment (multiple FSH-dose vs single-shot FSH treatment) and seasonality on embryo yields in fine-wool Merino ewes. Treatment based on multiple FSH-dose consisted of 200 mg of FSH (Folltropin(®)) administered in seven decreasing doses. Single-shot treatment consisted of a single dose of 70 mg of FSH + eCG. In ewes treated with multiple FSH doses, number of recovered embryos was higher (6.0 ± 0.5 vs 3.5 ± 1.0), while non-fertilization rate was lower (12.8 ± 3.9 vs 40.3 ± 9.5) during the breeding season when compared to the non-breeding season (p < 0.05); although similar values of recovered Grades 1-2 embryos were observed between seasons. During the breeding season, proportion of responding ewes (98.1 vs 57.1%), ovulation rate (13.9 ± 0.8 vs 3.2 ± 1.2), recovered structures (7.9 ± 0.6 vs 1.7 ± 0.7), total recovered embryos (6.0 ± 0.5 vs 1.2 ± 0.6) and good-quality embryos (5.1 ± 0.5 vs 0.9 ± 0.6) were higher for the multiple FSH-dose treatment than for the single-shot protocol. In a similar way, in the non-breeding season, ovulation rate (11.3 ± 1.8 vs 6.0 ± 1.1) and recovered structures (6.6 ± 1.2 vs 2.7 ± 0.6) were higher for the multiple FSH injections protocol than those for the single-shot treatment, resulting in higher recovered Grades 1-2 embryos (3.2 ± 0.9 vs 1.4 ± 0.5). Current results indicate that seasonal anestrus affected embryo yields when applying multiple FSH-dose superovulatory treatment in Merino ewes, by decreasing the number of recovered embryos although the number of recovered good-quality embryos was not affected. During both seasons, multiple FSH injections produced higher ovarian response and number of viable embryos than the single-shot treatment.