Summary. Oestrus was synchronized in ewes by (a) withdrawal of an intravaginal progestagen sponge after 12 days or (b) injection of PGF-2α on Day 11 of the oestrous cycle. In addition, ewes were treated with (a) no hormone, (b) 1500 i.u. PMSG 48 h before sponge removal or PG injection, or (c) 24 mg porcine pituitary FSH in multiple injections commencing 48 h before sponge removal or PG injection, in a 2 × 3 factorial design. Ewes were inseminated with 0·2 ml fresh undiluted semen into the neck of the cervix 48 h after sponge removal or PG injection. Normally cyclic ewes were similarly inseminated within 12 h of observed standing oestrus.
At 24 h after insemination one uterine horn and one oviduct were flushed for recovery of spermatozoa and ova. When compared with naturally cyclic ewes, PG synchronization resulted in a marked reduction in the numbers of spermatozoa recovered (P < 0·05), and sponge synchronization led to a small, non-significant, reduction. Within the synchronized ewes, PMSG and FSH resulted in an equivalent superovulatory response, but there was a marked reduction in sperm recovery when compared with unstimulated animals (P < 0·01), with the greatest reduction attributable to PMSG treatment. Spermatozoa were recovered from fewer ewes treated with PMSG than with FSH (P < 0·05). Despite the observed impairment of sperm transport, a high fertilization rate was observed within each group and there were no differences between treatments.