الفهرس 
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Abstract
This study aimed to:1-Assess the efficiency of different protocols of estrus synchronization programs on pregnancy rates in beef breeds of Angus Aberdeen and Herford cows and heifers and their crosses: nursing cows, open day cows and heifers. 2-Determine the best estrus /ovulation protocol that might be applied under Egyptian environmental condition. A 102 beef (Angus, Herford and their crosses) heifers(n=52) and cows(n=50 divided into; nursing=21 cows open day cows n=29) were used in the current study. all cows were cycling> 60days postpartum. The heifers were mature and they aged > 1.5 years and 5 bull for mating .The animals were randomly allotted into five experimental groups: group 1 which consisted of 15 nursing cows and 6 open day cows and 9 heifers(total no=30). Each animal in this group was treated with CIDR-COSync protocol : includes two injection of GnRH Receptal(2.5ml) on day 0 and 8.5 and PGF2α Lutalyse(5ml) injection on day6and CIDR was inserted intravaginally on 0 day and removed on 7 day the bull Introduce after injection of 2nd dose of GnRH Receptal
group 2: which contained 12 heifers and 6 open day cows(total no=18 )and treated with CIDR- PGF2α sync protocol. Each animal in this group was treated with Insertion of CIDR into vagina on of cows and heifers on 0 day . on day 6 , each animal received an Im injection of 25 mg Dinoprost (5ml Lutalyse) . Remove CIDR at day 7, one bull introduced after removal of CIDR
group 3: which contained 13 heifers and 5 open day cows(total no=18 )and treated with G-P-G Ovsync protocol .Which consisted of two injection of GnRH(10ug buserlin,Receptal2.5 ml) on days 0 and 9 and a single injection of PGF2α( Lutalyse 5 ml) on day 7 .The bull introduced at the same time of the second GnRH injection.group 4: which contain 6 open day cows and 12 heifers (total no=18 )and treated with injection of double PGF2α Lutalyse 5 ml/im/head. At 11 day interval The bull introduced after the 1st dose of PGF2α.
group 5 which contain6 nursing cows and 6 open day cows and 6 heifers(total no= 18). The animal in this group received 5ml/im injection of normal saline once at the beginningof the experment.This study summarized that:1-The results was (18) cows and(23) heifers pregnant from (84)cows and heifers estrus synchronized and the total percent of pregnancy is 48.8%. 2-The higher pregnancy rate observed in group (3) that treated with G-P-G Ovsync protocol (61.10). then followed by group 2 that treated with (CIDR- PGF2αSync and group 4 that treated with double dose of PGF2α with present of pregnancy 50%.followed and group 1 that treated with CIDR-COSync protocol (40 %).
While, the lower pregnancy rate observed in group (5) (control group) (27.8 %) 3- from this work we concluded that The best protocol to be used in Egyptian environment is COSync protocol for both open day cows(66.7%) and heifers(58.3%) Also the CIDR- PGF2α Sync gave the same results on open day cows(66.7%).
So in open day cows we can use CO Sync protocol or CIDR- PGF2α Sync protocol .
In heifers we use COSync protocol as best results.