Synchronization of follicular wave emergence in the seasonally anestrous ewe: The effects of estradiol with or without medroxyprogesterone acetate

Fertility is often lower in anestrous compared to cyclic ewes, after conventional estrus synchronization. We hypothesized that synchronization of ovarian follicular waves and ovulation could improve fertility at controlled breeding in anestrous ewes. Estradiol-17β synchronizes follicular waves in cattle. The objectives of the present experiments were to study the effect of an estradiol injection, with or without a 12-d medroxyprogesterone acetate (MAP) sponge treatment, on synchronization of follicular waves and ovulation in anestrous ewes. Twenty ewes received sesame oil (n = 8) or estradiol-17β (350 μg; n = 12). Eleven ewes received MAP sponges for 12 d and were treated with oil (n = 5) or estradiol-17β (n = 6) 6 d before sponge removal. Saline (n = 6) or eCG (n = 6) was subsequently given to separate groups of ewes at sponge removal in the MAP/estradiol-17β protocol. Estradiol treatment alone produced a peak in serum FSH concentrations (4.73 ± 0.53 vs. 2.36 ± 0.39 ng/mL for treatment vs. control; mean ± S.E.M.) after a short-lived (6 h) suppression. Six of twelve ewes given estradiol missed a follicular wave around the time of estradiol injection. Medroxyprogesterone acetate-treated ewes given estradiol had more prolonged suppression of serum FSH concentrations (6–18 h) and a delay in the induced FSH peak (32.3 ± 3.3 vs. 17.5 ± 0.5 h). Wave emergence was delayed (5.7 ± 0.3 vs. 1.4 ± 0.7 d from the time of estradiol injection), synchronized, and occurred at a predictable time (5–7 vs. 0–4 d) compared to ewes given MAP alone. All ewes given eCG ovulated 3–4 d after injection; this predictable time of ovulation may be efficacious for AI and embryo transfer.