Hormone Levels in Superovulated Prepuberal and

Pituitary and plasma luteinizing hormone (LH) and luteal and plasma progesterone were measured in 47 prepuberal Holstein calves and in eight postpuberal heifers for 30 days after induced ovulation or superovulation. Mean pituitary LH in six of the eight heifers sacrificed 30-31 days after superovulation averaged 1.1 mg LH/g of pituitary tissue. Plasma LH rose to 7.2 ng/ml the day after PMSG injection and gradually declined to normal levels of about 2 ng/ml. Plasma progesterone peaked at 63 ng/ml 10 days after LH injection to induce superovulation and declined to nearly undetectable levels in three of the heifers by Day 24. These three heifers ovulated spontaneously, plasma progesterone rose to 8.3 ng/ml by Day 28, and each had a new active corpus luteum at slaughter. The others had not ovulated when slaughtered on Day 30, and still had some old active luteal tissue. Mean pituitary LH in control calves was 5.0 mg/g of wet pituitary tissue and ranged from 0.7 to 1.6 mg/g during the 30 days after superovula-tion. Plasma LH in calves rose from 1.5 ng/ml before injection of pregnant mare serum gonadotropin (PM SC) to 5.5 ng/ml the day after PMSG and returned to the original level by 10 days after PMSG. Calf corpora lutea had a maximum average progesteron