الفهرس 
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Abstract
This work includes three main studies; 1) survey study, 2) diagnostic study, and 3) therapeutic study. The survey study (600 heifers) aimed at investigating the effect of birth and conception seasons on number of services per conception (NSC), age at 1st service (AFS) and age at 1st conception (AFC) as well as incidence of repeat breeding in Egyptian buffalo heifers (RBH). In the diagnostic study, oestrous and ovarian activities of virgin heifers (VH) and RBH were studied. In the therapeutic study, 30 RBH were exposed to three hormonal protocols including, GnRH on day of oestrus, GnRH- PGF2α -GnRH protocol and PGF2α - PGF2α protocol. Results show that NSC, AFS and AFC were 4.6 serv./conc., 22.6 mo and 27.27 mo, respectively PGF2α. This study indicated incidence of repeat breeding for more than 50% of heifers (based on number of inseminated animals) or 37% (based on total number of cyclic heifers). The effect of birth or conception season on NSC, AFS and AFC was not significant, but heifers conceived in winter showed the least NSC and the earliest AFS and AFC. Embryonic mortality occurred in 6 out of 30 RBH representing 20% of all RBH. All six RBH showing embryonic mortality at the 2nd oestrous cycles (100%), however, 2 out of them showed embryonic mortality at the 3rd cycles. No embryonic mortality cases were observed at the 1st and 4th cycles. Length of oestrous interval for all RBH showing embryonic mortality during the 2nd cycles ranged between 33 and 60 days, averaging 48 days. However, two RBH showed embryonic mortality at the 3rd cycles ranging between 45 and 50 days and averaging 47.5 days. from the economic point of view, the obtained results indicated the cheaper cost of PGF2α- PGF2α and GnRH at insemination protocols (180 and 200 L.E/group, respectively) than that of GnRH- PGF2α-GnRH protocol (420 L.E.). The current study indicated some differences between virgin and RBH in term of LBW at birth, age at 1st oestrus, oestrous cycle length and average P4 concentration during oestrous cycle, being with higher values in RBH than in virgin heifers. Repeat breeder heifers could be therapy treated by GnRH protocol at insemination or PGF2α-PGF2α (11-day interval) based on heat incidence to improve their reproductive performance, which may indicate that the main problem in incidence of repeat breeder cases was a disturbance in the time between onset of oestrus, ovulation and insemination. Using PGF2α-PGF2α protocol showed the best results (conception rate and costs) compared to the other protocols.