الفهرس 
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Abstract
Leptin hormone acts as a signal for energy status and reproduction, the current study investigated dynamics of gonadal steroids and leptin during estrous cycle in ewe, leptin gene polymorphism (Genotyping) of native sheep breeds and the correlation between leptin genotypes and sheep reproductive performance. Synchronization of estrous cycle in ewes was accomplished by insertion of intravaginal sponge (Chronogest; Intervet Ltd.,) for 14 days followed by I/M injection of 300 IU equine Chorionic Gonadotropin (Folligon; Intervet Ltd.,) for each ewe on day of sponge removal (day 0), blood samples were collected during estrous cycle for determination of leptin, estradiol and progesterone hormones by ELISA technique. For analyzing leptin gene polymorphism and its association with reproductive traits in Ossimi and Rahmani sheep, blood samples of 50 ewes (25 Ossimi and 25 Rahmani) belonging to Research Institute of Animal Production (Sakha station, Kafr El-Sheikh) were collected. PCR was performed to amplify 275 bp fragment of exon 3 from leptin gene. Then Single Strand Conformation Polymorphism (SSCP) of PCR product was performed and leptin band patterns (genotypes) were obtained using acrylamide gel and silver staining. The obtained results showed fluctuation in levels of leptin, where a significant decrease was recorded during follicular phase and an increase during luteal phase. Estradiol levels were highest during 1st 2 days of the 17 and 18 days estrous cycle, reached lowest levels during days 7, 9, 11, 13 and 15 of the 17 days estrous cycle. As for the 18 days estrous cycle the estradiol level remained low for one more day (17th day). Progesterone levels were lowest during first 3 days of the 17 days estrous cycle, while during the 18 days estrous cycle, low progesterone levels were detected up to the fifth day of the cycle; progesterone peaked at day 11 of the 17 and 18 days estrous cycle. Single Strand Conformation Polymorphism revealed two genotypes AA and BB in Ossimi breed with frequency 16% and 84% respectively and only AA genotype in Rahmani breed. BB genotype showed higher weight at first service, higher conception rate, short gestation period and higher weight at lambing while animals having AA genotype showed clearly estrus signs during season.