Effect of season and duration of FSH treatment on embryo production in sheep

Abstract

Thirty-six mature Manchega ewes were used in two experiments to determine the effect of season and of 2- or 3-d FSHp treatment on the ovulation rate and number of transferable embryos produced. During the breeding season, estrus was synchronized with FGA (30 mg for 13 d). Begining 48 or 24 h before sponge removal, each ewe received two daily injections of 4-4-3-3-1-1 or 5-5-3-3 mg of FSHp. Concurrently with the two last injections both groups were administered 100 μg of LH. Ewes were tested for estrus and 6 or 7 d later were laparotomized and surgically flushed to recover embryos. The number of corpora lutea (CL), the total number of embryos and of viable embryos were recorded. Six months later (nonbreeding season) the design was repeated, with each ewe receiving the opposite treatment to that received in the fall. Response in ovulation rate and number of viable embryos did not differ between seasons. Mean (SEM) numbers of observed CL and embryos recovered were higher (P<0.001) with the 3-d treatment (8.7±5.8 and 7±4.8) than with the 2-d treatment (5.8±3.2 and 4.4±3) when pooled over the two seasons. The mean number of transferable embryos was higher (P<0.01) with the 3-d (4.2±3.9) than with the 2-d treatment (2.5±2.3).