PLASMA PROGESTERONE PROFILES, OVARIAN RESPONSE AND EMBRYO RECOVERY INCROSSBRED EWES SUPEROVULATED DURING BREEDING AND NON-BREEDING SEASONS

Corriedale X Nali ewes were superovulated using a Synchromate-B-FSH(E) -GNRH regimen and the embryos were collected surgically at Day 6 post oestrus. Plasma progesterone levels were monitored during the breeding season (n=6) and the non-breeding season (n=7) and the correlations b etween hormone profiles and embryo production parameters studied. Init ial mean progesterone levels, before insertion of Synchromate-B (now C RESTAR) implants, were significantly higher during the breeding season (1.23 +/- 0.31 ng ml(-1)) compared with the non-breeding season (0.36 +/- 0.03 ng ml(-1)). The lowest values were recorded in both superovu lated ewes (0.11 +/- 0.06 and 0.09 +/- 0.02 ng ml(-1) during the two s easons) and normal cyclic ewes (0.24 +/- 0.08 ng ml(-1)) at the onset of oestrus. Day 6 concentrations were not different between seasons, b ut significantly higher (P<0.05) in superovulated ewes compared with n ormal cyclic animals. Deviations of progesterone profiles affected the embryo recovery and transferable embryos. A positive, significant, co rrelation was observed between hormone concentration on the day of ini tiation of superovulatory treatment and transferable embryos (r=0.641) , and the levels on the day of flushing correlated with ovulation rate (r=0.661) and embryo recovery (r=0.553). It is concluded that progest erone deviations adversely affect embryo recovery and quality.