HORMONAL CONTROL OF REPRODUCTION IN EWES DURING THEIR NORMAL BREEDING SEASON

Abstract

Injected or orally-administered progestagens have been shown to synchronize estrus in mature ewes during their normal breeding season. Oral administration of 6–methyl-17-αα-acetoxyprogesterone (MAP) or 6-chloro-Δ6-dehydro-17-acetoxyprogesterone (CAP) for 10 days was more effective in synchronizing estrus than intramuscular injections of repositol progesterone. CAP appeared to be more active in controlling breeding activity than MAP (2.5 mg CAP per head vs. 60 mg MAP per head). The administration of 2.5 mg CAP per head per day for 18 days was as effective as the feeding of 3.5 mg per head per day for 10 days. CAP, at a dosage level of 2.5 mg, administered over a 10-day period to motivate first post-treatment estrus, was more effective when injected intramuscularly than when administered orally. The administration of Pregnant Mare Serum did not result in an increase of lambing percentage.