Abstract
Ova were found in the oviducts of 80% of immature mice at 0400 hours on day 4 following the subcutaneous injection of 5 iu of pregnant-mares' serum gonadotrophin (PMSG) on day 1. When sodium barbitone was administered between 14 30 and 16 00 hours on day 3 the percentage of animals ovulating on day 4 was reduced. Halothane anaesthesia did not inhibit ovulation when given between 08 30 and 17 30 on day 3. Neither anaesthetic altered the mean ovum count.