Blood LH level and induced ovulation after hCG and PMSG treatment in ovarian quiescent cattle

Ovarian quiescent cattle bearing follicle with palpable size were treated with single intramuscular injection of 750-6,000 IU of human chorionic gonadotrophin (hCG) in 13 cases and 1,000-2,000 IU of pregnant mare serum gonadotrophin (PMSG) in 5 cases. Changes of blood luteinizing hormone (LH) level, estrus and ovulation after the treatments were examined. After the hCG treatment LH level became slightly high from 0.2-0.6 ng/ml of pre-treatment to 0.3-1.9 ng/ml of post-treatment and maintained the level up to ovulation without the ovulatory LH surge. Ovulation was induced about 36 hr after the treatment in 12 cases. The ovulations were all silent ovulations. After the PMSG treatment LH level became slightly high from 0.6 ng/ml of pre-treatment to 1.3 ng/ml of post-treatment and the level lasted until the ovulatory LH surge. The ovulatory LH surge occurred about 39 hr after the PMSG treatment in 4 cases with a peak of about 32 ng/ml. Ovulation was induced about 74 hr after the treatment in all 5 cases. Four cases showed estrus but one in which the LH surge could not be confirmed did silent estrus preceding the induced ovulations. It was demonstrated that hCG induced ovulation without the LH surge but PMSG induced the ovulatory LH surge and the subsequent ovulation in ovarian quiescent cattle.