الفهرس 
Reproductive Performance and Physiological Responses to Different Estrus Synchronization Protocols in Dairy CowsOnly 14 pages are availabe for public view
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Abstract
This study was designed to determine the efficiency of three different protocols of estrus synchronization on reproductive performance of postpartum dairy cows. Sixty-four postpartum Holstein dairy cows (days in milk, DIM: 45 days) were randomly assigned to four groups. First group (CIDR-eCG, n:16) the internal progesterone releasing (CIDR) devices were injected at the time of CIDR withdrawal. Estrus detection was conducted after 24-72hr from injection. Second group (CIDR-PGF2α, n:15) CIDR were inserted for 8 days and 500 μg Cloprostenol (PGF2α) were injected one day before CIDR withdrawal, and estrus signs were detected through 24 – 72 hr after CIDR removal. Third group (CIDR-Ovsynch, n:15) CIDR were applied with the first injection of GnRH and were removed with PGF2α injection. Cows were time-inseminated with frozen thawed semen 16-20 h after the second injection of GnRH. Fourth group (Control, n:18) cows remained without hormonal treatments, estrus signs were observed from parturition to confirmation of pregnancy or until 100 days in milk (DIM). Using CIDR-eCG or CIDR-OVS protocols improved ovarian activity as presented in increasing (P < 0.05) total number of follicles compared to CIDR-PGF2α and control groups. Nevertheless, CIDR-eCG protocol was superior in reducing (P < 0.05) number of small follicles and increasing (P < 0.05) number of large follicles compared to CIDR-OVS protocol. The pronounced luteotrophic effect of CIDR-eCG and CIDR-OVS protocols expressed as greater (P < 0.05) P4 concentration compared to both of CIDR-PGF2α and control groups, between which no significant difference was observed. While CIDR-eCG, CIDR-OVS and CIDR-PGF2α groups increased (P < 0.05) E2 concentration compared to that of control.