الفهرس 
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Abstract
This study was carried out at Physiology Department, Faculty of Veterinary Medicine, Mansoura University in cooperation with El-Serw Waterfowls Research Station, Damietta, Animal Production Research Institute. A total number of one hundred and sixty eight (168) Domiaty ducks aged 24 wk old (144 females and 24 drakes) were monitored from this station at 4 different ages (24, 32, 40, 48 wk old). Ducks were leg banded, individually weighed and randomly divided into six equal pens; each pen contained 28 ducks and the following measurements were determined: Egg production including egg number, egg production rate, egg weight, egg mass during three periods (24-32wks, 32-40wks, and 40-48 wks).Egg traits and egg hatchability traits (fertility %, embryonic mortality (early mortality, late mortality, pip dead, and total mortality), and hatchability %). f plasma levels of estrogen hormone and both calcium and phosphorus in were determined at 24, 32, 40 and 48 wk old. Bone development of duck embryo at 19 d old of incubation and Performance of young ducklings through: body weight, body weight gain, feed consumption, feed conversion ratio, proteins and lipids profile and carcass traits. The results of this study revealed that: Egg production of ducks showed significant changes with advancing age, egg production rate and egg number significantly decreased, Although, egg weight significantly increased and egg mass didn’t show any significant difference. Most egg traits were affected significantly by ducks age. Egg weight, yolk weight and %, albumin weight, shell weight and thickness, ESI % significantly increased with advancing duck age. But albumin %, yolk index and HU decreased as reproductive season progress. Fertility% significantly increased with age. However, egg hatchability % didn’t show any significant difference at 4 different ages. Plasma level of estrogen decreased significantly with duck age, but phosphorous level significantly increased and calcium level showed significant variation at different duck ages. Generally, bone characters’ of tibia and femur were better in middle-aged breeders (32, 40) wk old when compared to the beginning of laying cycle (24wks) and near the end (48wks). Young ducklings performance: ducklings weight at hatch significantly increased with age. However, ducklings weight % of egg did not show any significant variation. BWT, BWG and F.C increased significantly in young duckling from 24 and 32 wk old duck breeder when compared to older breeder 40, 48 wk old. However, FCR of young duckling through (0-10) wk old in this study showed a significant increase with advancing age. Serum total proteins and albumin significantly increased in young ducklings from younger ducks (24, 32) wk old, when compared to young ducklings from older breeder.