الفهرس 
CONTENTSOnly 14 pages are availabe for public view
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Abstract
This study focused on the various methods for controlling Estrous cycles in well-managed dairy cows. Because up to 70% of dairy cows may stay non-pregnant after an AI procedure, an effective approach for identifying and reinseminating open cows is essential for dairy herds to achieve optimal reproductive performance. In Egypt, a widely used programme involves starting the Ovsynch protocol (0 day GnRH-7 d-PGF2-56 h-GnRH-16 to 20 h-AI). The present study aimed to evaluate how the application of presynch, and modified presynch protocols would be used to maximize the reproductive performance of holstein dairy cows in Egypt. The study carried on 412 holstein dairy cows divided to four groups according to synchronization protocol. Group(1): 117 cows received Ovsynch protocol with GnRH. Group(2): 113 cows received modified Ovsynch protocol with PMSG. Group(3): 98 cows received Presynch Ovsynch protocol with GnRH. . Group(4): 84 cows received modified Presynch Ovsynch protocol with PMSG. Blood sample collected at every hormonal treatment for estimation of progesterone, estradiol and cortisol. Then 28 days after an initial AI pregnancy diagnosis by TRUS and confirm pregnancy 60 day after AI by rectal palpationThe previous results showed that the use of the presynch either by using GnRH and/or PMSG plays an important role in the improvement of the reproductive performance., ovulation rates and serum progesterone at the time of PFG shots. Fourth group is the highest conception rate.