Effects of GnRH and hCG treatments for enhancing corpus luteum function to increase lambing rate of ewes artificially inseminated during the non-breeding season

摘要

Two experiments were conducted to enhance the corpus luteum (CL) function for increasing lambing rate of ewes treated with GnRH or hCG after artificial insemination (AI) during the non-breeding season. Ewes (Experment 1:n=102, Experiment 2:n=37) were pretreated with a controlled internal drug release dispenser (CIDR) for 12 days and 500 IU equine chorionic gonadotropin (eCG) 1 day before CIDR removal. In Experiment 1, the ewes were treated on Day 12 (Day 0=CIDR removal): 1) Group I; GnRH (100#mu#g), 2) Group II; hCG (500 IU), 3) Group III; 0.6 percent saline (2 ml) for control. Pregnancy and lambing rates and prolificacy were not significantly different among the groups. But, there was significant (P<0.01) difference in the lambing rate between parous (27 percent) and non-parous (72 percent) in Group I. On Day 17, plasma progesterone (P_4) levels of Group I were significantly (P<0.01) lower than those of Group III, but on the contrary, the plasma P_4 levels of Group II were significantly (P<0.01) higher than those of Group III. In Experiment 2, the ewes were treated: 1) Group I; hCG (500 IU) on Day 6, 2) Group II; hCG (500 IU) on Day 9, 3) Group III; no treatment for control. Pregnancy and lambing rates and prolificacy were not significantly different among the groups, but on Days 12 and 15, the plasma P_4 levels of Groups I and II were significantly (P<0.01) higher than those of Group III. The present results indicate that a single hCG treatment on Days 6, 9 and 12 after CIDR removal stimulates CL and increased P_4 concentration, but the increased P_4 levels did not reflect on the fertility of treated ewes.