Abstract
Total of 40 crossbred ewes were divided into five treatment groups (8 ewes each). Ewes in the first group (G1) represented the control ewes which were allowed for natural mating. The control ewes were exposed to fertile ram from the contemporary to that of treatment groups start time up to the end of the breeding season (end of September) and natural mating was applied for those coming in estrus. Ewe in the other four treatment groups G2, G3, G4 and G5 treatment groups were inserted with 20 mg sponges for 11 days, and ewes in G2 were injected with 300 IU PMSG on the Day 11 (sponge withdrawal), ewes in G3 the same treatment of G2 but injected with 1 ml progesterone (Lutone) before the sponge withdrawal with 24 h (Day 10), ewes in G4 after sponge withdrawal teaser introduce ram kept until artificial insemination was done. Ewes in G5 the same treatment of G4 but injected with 1 ml progesterone (Lutone) before the sponge withdrawal with 24 h (Day 10). Ewes in all treatment groups were artificially inseminated twice 48 and 56 hr after the sponge removed with fresh diluted semen. Blood samples were taken during treatment period for P4 assay. Results show that estrus rate was 100% in treatment groups and onset of estrus was the latest (P<0.05) with the longest duration (P<0.05) in ewes of G5, while those in G2 showed an opposite trend. Lambing rate was the highest (P<0.05) in G2 and G5 (75%), moderate in G3 and G4 (62.5%) and the lowest in G1 (50%). Ewes in G3 showed the highest (P<0.05) fecundity and twining rates (112.5% and 1.80 lamb /ewe) due to the greatest number of twins as compared to other treatment and control groups. The differences in average LBW of lambs at birth between all treatment groups and the control one were not significant. There was marked differences in P4 level according to treatment and lambing in different groups. In conclusion, the findings of the present research indicate that primary P4 and PMSG is a beneficial adjunct to the breeding of sheep by AI at progestagens-synchronized estrus and administration of 300 IU PMSG at sponge withdrawal is more effective for increasing the reproductive performance of artificially inseminated crossbred ewes in breeding season.
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