Effect of human chorionic gonadotropin on induced ovine corpora lutea during the anestrous season

Experiments were conducted to determine the effect of additional gonadotropic support on induced corpora lutea of anestrous ewes. In one series of experiments, ewes were superovulated and half the ewes received an i.v. injection of 500 IU human chorionic gonadotropin (hCG) on day 5 after ovulation. Corpora lutea were collected from both groups on day 10 after ovulation. Dissociated corpora lutea collected from ewes which received additional hCG contained proportionately more large luteal cells than did those from control ewes (P<.05). In neither cell type was content of receptors for luteinizing hormone (LH) or secretion of progesterone in response to LH affected by an additional injection of hCG. Large cells from anestrous ewes produced more progesterone in response to LH (P<.05) than did large cells from similarly treated ewes during the breeding season. Small cells collected during either season responded similarly to LH. In another series of experiments, anestrous ewes were induced to ovulate and were exposed to fertile rams. Half the ewes received an i.v. injection of 500 IU hCG on day 5 after ovulation. Serum content of progesterone was higher on day 10 in ewes which received hCG 5 days earlier than in control ewes, although progesterone levels declined to generally nondetectable levels in nonpregnant ewes of both groups by day 16. Pregnancy rates in the two groups were not different. We concluded that additional gonadotropic support affects the morphology and function of corpora lutea from anestrous ewes and may be useful for enhancing fertility during the nonbreeding season.