Control of the Estrous Cycle with Prostaglandin F2α in Cattle and Horses

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Abstract
After depositing 5 mg PGF2α 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 PGF2α into heifers during diestrus caused similar results, but administration of PGF2α on day 3 of the estrous cycle had no luteolytic effect. Intravaginal treatment with 30 mg PGF2α resulted in luteolysis which was more variable and retarded by about 1 day compared to that after im PGF2α. The fertility of cattle inseminated during the estrus after treatment with PGF2α and that of cattle inseminated at 72 and 90 hr., after PGF2α was equivalent to that in controls. After im injection of PGF2α, 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 PGF2α, and estradiol increased continuously possibly beginning within 1 hour. Intramuscular injections of PGF2α 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 PGF2α; GH increased two and one-half-, seven- and 26-fold at 30 min. after 15, 30 and 60 mg PGF2α. Increased growth hormone (GH) persisted for at least 2 hr. after in PGF2α. Relative to changes after im PGF2α, infusion (iv) of 0.5 mg PGF2α per minute for 30 min. resulted in higher blood prolactin and GH. In horses, administration of 10 mg PGF2α 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. PGF2α 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 PGF2α may allow artificial insemination in herds where AI was not possible previously. However, effects of PGF2α on other than reproductive traits should be investigated more thoroughly.

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