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Control of the Estrous Cycle with Prostaglandin F₂ in Cattle and Horses¹

Michigan State University², East Lansing 48823

Abstract

After depositing 5 mg PGF₂ into the uterus of cows during diestrus, progesterone fell 50% within 12 hr., estradiol more than doubled within 24 hr., LH peaked at 71 hr., estrus began at 72 hr. and ovulation occurred at 95 hours. Intramuscular injection of 30 mg PGF₂ into heifers during diestrus caused similar results, but administration of PGF₂ on day 3 of the estrous cycle had no luteolytic effect. Intravaginal treatment with 30 mg PGF₂ resulted in luteolysis which was more variable and retarded by about 1 day compared to that after im PGF₂. The fertility of cattle inseminated during the estrus after treatment with PGF₂ and that of cattle inseminated at 72 and 90 hr., after PGF₂ was equivalent to that in controls.

After im injection of PGF₂, blood plasma PGF peaked from 10 to 30 min. and declined to basal values within 2 hours. Blood plasma progesterone began to fall within 10 min. and continuously after PGF₂, and estradiol increased continuously possibly beginning within 1 hour. Intramuscular injections of PGF₂ caused an increase in blood prolactin (2.5-fold within 10 min.) which persisted for at least 2 hours. Increases in GH were proportional to im dose of PGF₂; GH increased two and one-half-, seven- and 26-fold at 30 min. after 15, 30 and 60 mg PGF₂. Increased growth hormone (GH) persisted for at least 2 hr. after in PGF₂. Relative to changes after im PGF₂, infusion (iv) of 0.5 mg PGF₂ per minute for 30 min. resulted in higher blood prolactin and GH.

In horses, administration of 10 mg PGF₂ into the uterus or 15 mg sc at day 7 to 9 after ovulation caused a 60% reduction in blood progesterone within 12 hr., estrus commenced in about 2.2 days and ovulation occurred at about 2 days before the end of estrus.

PGF₂ had no detectable or significant residual influence on the subsequent control estrous cycles in either cows or horses. The precise synchrony of ovulation and normal fertility after administration of PGF₂ may allow artificial insemination in herds where AI was not possible previously. However, effects of PGF₂ on other than reproductive traits should be investigated more thoroughly.

¹ Published with the approval of the Director of the Agricultural Experiment Station as Journal Article No. 4680; supported in part by USPHS Research Grant HD 06948. Dr. B. E. Seguin, Dr. D. A. Morrow and Mr. J. N. Stellflug participated in portions of this research.

² Department of Dairy Science.