Controlled Superovulation in Dairy Heifers Using Prostaglandin F2α and Pregnant Mare Serum Gonadotropin1

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Abstract
Twenty-four sexually mature dairy heifers in six groups of four each received 25 mg of prostaglandin F2α (PGF2α) 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 PGF2α and half were given the hormone 12 hr later to determine if the ovarian response would be affected by reduced progesterone following PGF2α-induced luteal regression. Ovulation rate was not affected by changes in progesterone prior to PMSG. Each of the eight animals receiving only PGF2α or PGF2α 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). Copyright © 1978. American Society of Animal Science . Copyright 1978 by American Society of Animal Science.