Suppression of oestrus in sheep with progesterone

Abstract

Progesterone in oil was given intramuscularly to groups of Merino ewes during the autumn breeding season in order to test various dosage levels and injection intervals for suppression of oestrus. Mean daily doses were 5, 10, or 20 mg. given either daily, or as a double dose every second day, or as a quadruple dose every fourth day. The follovving results were obtained:

1. Injections daily or every 2 days suppressed oestrus in most ewes. Injections every 4 days were less successful. There was a significant tendency for ewes in late cycle at the time of the first injection to come into oestrus at their expected date.
2. The intervals between the last injection and oestrus for the 5 mg mean daily dose were 1.6 days (daily injection) and 2.0 days (injection every 2 days); for the 10 mg dose 2.3 and 2.6 days; and for the 20 mg dose 3.8 and 4.4 days.
3. Of 19 ewes which mated during the injection period only one lambed.
4. Fertility in ewes mated after the injection period was greatest in those given injections of progesterone every 2 days.