Effect of two doses of progesterone on estrus response and fertility in acycling crossbred Bharat Merino ewes in a semi-arid tropical environment

The efficacy of two doses of progesterone (P4), i.e. 350 and 300 mg was evaluated in acycling crossbred ewes (50) during the autumn breeding season. Ewes were treated with intravaginal progesterone sponges with either 350 mg or 300 mg for 12 days. At standing estrus, ewes were hand mated (three cycles). Progesterone (350 mg) gave a better (P<0.05) estrus response (75%), compared to 300 mg dose (42%). Ewes treated with 350 mg P4 also showed better (P<0.05) synchronization response (93%) than those treated with 300 mg (56%) at 72 h after sponge removal. Lower doses of progesterone (300 mg) significantly delayed (P<0.01) the onset of estrus. However, dose had no significant influence (P>0.05) on estrus length, conception rate and the proportion of ewes lambing at term, This study indicates that dose of progesterone may have an effect on estrus exhibition and response time without altering the conception rate and lambing in acycling crossbred Bharat Merino ewes during the major breeding season in a semi-arid tropical environment. (C) 2000 Elsevier Science B.V. All rights reserved.