Ovarian response, ova recovery and fertility in merino ewes superovulated either during the luteal phase of their oestrous cycle or after intravaginal progestagen treatment.

Five groups of merino ewes were treated with 1000 i.u. of pregnant mare serum gonadotropin (PMSG) as a single injection per ewe. Three of these groups received treatment on days 7,9 and 11 of their oestrous cycle. Oestrus was synchronized with 125 mg of prostaglandin F2(alpha) (PG) given two days after PMSG. Oestrus in the other two groups was synchronized by intravaginal progesterone sponges inserted for 14 days. In one group, the sponges were inserted nine days after oestrus onset. In the other group the stage of the oestrous cycle was unknown. In both these groups, PMSG was given a day prior to sponge removal. No significant differences were recorded for either the mean numbers of corpora lutea, unovulated follicles or ova recovery between the five groups. However, progestagen synchronized ewes yielded significantly more fertilized ova (p < 0.05) than PG synchronized ewes.