2002 Volume 48 Issue 5 Pages 497-504
The present study was conducted to determine the effect of a low dose of human chorionic gonadotropin (hCG) on the induction of fertile estrus in Shiba goats pretreated intravaginally with progesterone during the early postpartum period. Nursing Shiba goats (n=13) around 3 weeks after the parturition were pretreated with a controlled internal drug release dispenser (CIDR) containing 0.3 g of progesterone for 7 day, and 60 μg of cloprostenol 24 hr before CIDR removal. Goats in Group I (n=6) received subcutaneous injections of a low dose of hCG (1 IU/kg) after the removal of CIDR at 12-h intervals until the occurrence of estrus. Goats in Group II (n=7, control) received subcutaneous injections of saline instead of hCG. The rate of estrus induction in Group I (83.3%) tended to be higher than that in Group II (42.9%), although the difference was not significant (P=0.14). Time from the removal of CIDR to the beginning of estrus in Group I was significantly shorter than that in Group II (P<0.05). A prominent peak of estradiol-17 β concentration in plasma was observed with a maximum value at 30 h after the removal of CIDR in Group I, while two relatively small rises were detected with a maximum value at 48 h in Group II. The pregnancy rate in Group I (83.3%) was significantly higher (P<0.05) than in Group II (28.6%). These results suggest that the injections of low dose hCG after the treatment with CIDR promote follicular maturation and fertile estrus induction in the goats during the early postpartum nursing period.
