Abstract
The present study was conducted to determine the effect of two human chorionic gonadotropin (hCG) treatments on the fertility of ewes which were estrus-induced and artificially inseminated during the non-breeding season. Suffolk (SF: n=68) and South-Down (SD: n=20) ewes were pretreated with a controlled internal drug release dispenser (CIDR) for 12 days and 500 IU equine chorionic gonadotropin 1 day before CIDR removal. Each breed of ewes were divided into 3 groups: Group I (n=31), an intramuscular injection of 100 IU hCG was given on Days 3, 4 and 5 after artificial insemination (AI) (Day 0=the day of AI); Group II (n=29), an injection of 300 IU hCG was given on Day 4; and Group III (n=28, Control), an injection of 0.6% saline was given on Day 4. Plasma progesterone (P4) concentrations were measured by enzyme-immunoassay in all ewes in the three groups at the time of insemination (Day 0), and Days 4, 8, 12, 16, and 20 after AI. On Day 8, the mean P4 concentrations in ewes treated with hCG (Groups I and II) were significantly higher (P<0.01) than in the control ewes (Group III). In Group II, the mean P4 values on Days 14 and 18 were also higher (P<0.05) than those in the control ewes. Pregnancy (Days 20 and 58) and lambing rates were not significantly different among the three groups (37.9%, 55.2% and 54.2% for lambing rates). Prolificacy was also not significantly different among the three groups (1.36, 1.75 and 1.62). These results indicate that the present hCG treatment did not enhance fertility of the inseminated ewes, although the treatment stimulates corpus luteum and increased P4 concentrations.
