الفهرس 
Controlled reproduction during sheep breeding seasonOnly 14 pages are availabe for public view
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Abstract
This study was carried out at Sakha Animal Production Research Station, Kafrelsheikh Governorate, belonging to Animal Production Research Institute, Agricultural Research Center, Ministry of Agriculture in cooperation with Department of Animal Production, Faculty of Agriculture, Mansoura University, during the period from August, 2012 to November, 2013. This study included two experiments to evaluate the effect of some hormonal protocols on reproductive performance of ewes during September (1st experiment) and May breeding season (2nd experiment). First experiment (September 2012): This experiment was carried out during September breeding season from 15/8/2012 to 30/9/2012. Total of 40 crossbred ewes were used in this study. Ewes were divided into five similar treatment groups (8 ewes/group) according to age, body weight and physiological condition.
Second experiment (May 2013): This experiment was carried out during May season from 15/4/2013 to 30/11/2013. Total of 48 crossbred ewes were used in this study. Ewes were divided into six similar treatment groups (8 ewes/group) according to age, body weight and physiological condition.
The main results can be summarized as followed:
1. First experiment (September breeding season):
• Results show that all ewes (100%) in each treatment group responded to treatment and exhibited estrus. However, estrus rate was significantly (P<0.05) higher in all treatment groups (G2-G5) than in control one (G1), being 100 vs. 50%.
• Results show that pregnancy and lambing rates were significantly (P<0.05) higher in control ewes (G1) than in all treated ewes (G2-G5), being 100, 75, 62.5, 62.5 and 75% in G1, G2, G3, G4 and G5, respectively.
• Results showed that the effect of treatment on type of births produced was significant (P<0.05). Only ewes in G2 showed percentage of single and twin lambs similar to the control group. However ewes in G3 produced significantly (P<0.05) the highest percentage of twin lambs as compared to other treatments and control group.
• In G2 and G3, P4 concentration was higher in pregnant than in non-pregnant ewes and increased thereafter in pregnant indicating ovulation and pregnancy incidence, but P4 reduced in non-pregnant after sponge removal.
2. Second experiment (May breading season):
• Results show significant (P<0.05) of treatment on estrus rate of ewes. Estrus rate was significantly (P<0.05) higher in G2, G3 and G6 than that in the control group (G1). However, estrus rate did not differ significantly in G4 and G5 from that in G1.
• Results show that average time of estrus onset from sponge withdrawal was and estrous duration were affected significantly (P<0.05) by treatment.
• Results show that pregnancy and lambing rates were significantly (P<0.05) higher in control ewes (G1) than in all treated ewes (G2-G6), being 100, 85.7, 50.0, 50.0, 33.3 and 75% in G1, G2, G3, G4, G5 and G6, respectively.
• P4 level of the control ewes was above 0.1 ng/ml during early period of May season, such trend indicated incidence of ovarian activity for some ewes in the control group during May season.
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 September breeding season. In May season, progestagens-synchronized estrus (long term for 12 d or short term for 6 d) and administration of 500 IU PMSG at sponge withdrawal improved the reproductive performance of artificially inseminated crossbred ewes