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Controlled Superovulation in Dairy Heifers Using Prostaglandin F₂ and Pregnant Mare Serum Gonadotropin¹

Cornell University, Ithaca, NY 14853

Abstract

Twenty-four sexually mature dairy heifers in six groups of four each received 25 mg of prostaglandin F₂ (PGF₂) between days 7 and 14 of the estrous cycle. The control heifers received only this hormone; the other groups of heifers received 500, 1,200 or 2,000 IU of pregnant mare serum gonadotropin (PMSG). Half of the animals in the two latter groups received the PMSG simultaneously with the PGF₂ and half were given the hormone 12 hr later to determine if the ovarian response would be affected by reduced progesterone following PGF₂-induced luteal regression. Ovulation rate was not affected by changes in progesterone prior to PMSG. Each of the eight animals receiving only PGF₂ or PGF₂ plus 500 IU of PMSG had one ovulation. The average ovulation rate for eight animals receiving 1,200 IU of PMSG was 3.2 (range 1 to 6) and for eight receiving 2,000 IU of PMSG it was 5.6 (range 1 to 19). Duration of increased plasma progesterone concentrations, particularly following the highest dose of PMSG, seems to be more important in determining ovarian response than changes in progesterone prior to PMSG treatment. However, plasma concentrations of estradiol, progesterone and LH did not differ significantly among groups of heifers. Systemic concentrations of plasma progesterone were correlated with the number of corpora lutea 13 days after treatment (r=.99, P<.001).

¹ The authors thank International Cryo-Biological Services, Inc. for financial support, Dr. J. W. Lauderdale of The Upjohn Co. for the prostaglandin F₂, Dr. A. Campbell and Dr. K. Kirton of the Upjohn Co. for the conjugate used to produce the antibody to progesterone, the Endocrine Study Section, NIH for the PMSG and Eastern A.I. Coop., Inc. for performing the inseminations. The technical assistance of Dr. }. E. Hixon, Dr. W. R. Butler, G. S. Heckman, D. L. King, R. D. Koos, R. R. Saatman, M. J. Simkin and R. J. Wall is much appreciated.

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