الفهرس 
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Abstract
In order to clarify certain causes of postpartum estrous delay affecting reproduction in cattle, the study was carried out to study the relationship between certain hormones as leptin, cortisol and resumption of postpartum ovarian cyclicity. The study was carried out in the Department of Physiology, Faculty of Veterinary Medicine, Zagazig University . After obtaining blood samples from cows (n=20) in Sharkia govemorate during winter and summer seasons, the animals were divided into four equal groups (Five cows for each group): Group1: Farm animals reared on balanced ration showing resumption of postpartum ovarian cyclicity between 50d- 75d postpartum during winter season. Group2: Farm animals reared on balanced ration showing resumption of postpartum ovarian cyclicity at 75d postpartum during summer season. Group 3: animals from farmer’s houses reared on unbalanced ration showing delayed resumption of postpartum ovarian cyclicity after 75d postpartum during winter season. Group 4: animals from farmer’s houses reared on unbalanced ration showing delayed resumption of postpartum ovarian cyclicity after 75d postpartum during summer season. Blood samples were collected from jugular vein of these animals at (9 a.m) in tubes without anticoagulant ,preserved in ice boxes in slopped position, left at room temperature for two hours