The main aim of the current study was to evaluate the effect of GnRH administration on day five after mating as well as PGF2α injection at the time of CIDR removal on the reproductive performance of Ghezel ewes. Estrus synchronization was performed using an intravaginal application of CIDR for 14 days and injection of 500 IU of PMSG at the time of CIDR removal. A total of 114 healthy fat-tailed ewes were randomly allotted into three groups as follow: control group (n = 35), did not receive any additional treatment; PG group (n = 44), each ewe received a dose of PGF2α at the time of CIDR removal; and PG+GnRH group (n = 35), the ewes received a dose of PGF2α at the time of CIDR removal and a single dose of GnRH, five days post-mating (post-conceptional day (PCD)- 5). Body condition score (BCS) of total ewes was determined at the time of CIDR insert. Blood samples were collected on PCD-19 for determining the serum progesterone levels. All the ewes were examined by transrectal ultrasonography 30-35 days after mating for pregnancy diagnosis. The serum values for P4 concentration were in control, PG and PG+GnRH groups 6.34 ± 1.17, 9.19 ± 2.55 and 10.57 ± 2.0 ng/mL respectively. The PG+GnRH treatment significantly increased the litter size compared to the control group (P = 0.04), but there were no significant differences in another reproductive indices between experimental groups. The multiple birth, twin, fecundity rates and litter size (P = 0.05, p = 0.03 and p = 0.003 respectively) were significantly higher in ewes with BCS > 2 compared to ewes with BCS ≤ 2. It is concluded that GnRH on PCD-5 treatment in addition to PGF2α injection at the time of CIDR removal could improve reproductive performance of Qezel ewes during non-breeding season.
Keywords: Ewe; GnRH; PGF2α; Reproductive performance.
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