Reproductive Physiological Responses of Cattle to Exogenous Prostaglandin F2 α

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Abstract
Prostaglandin F2.alpha. [PGF2.alpha.] caused rapid regression of the corpus luteum and initiated normal transitory hormonal patterns that culminated in ovulation. PGF2.alpha. was effective in heat stressed heifers, and a thermal stress of 32.degree. C caused no major hormonal alterations from the time of CL [corpus luteum] regression to ovulation. A luteolytic dose of PGF2.alpha. tham salt (33.5 mg) given i.m. caused no major alterations in blood pressure, heart rate and uterine or aortic blood temperatures. The same dose given as an i.v. jugular infusion over a 2 min period caused major alterations in circulatory homeostasis and body temperature. Treatment of all cattle twice with PGF2.alpha. tham salt (33.5 mg), 12 days apart, increased the number of responsive heifers at the 2nd PGF2.alpha. injection. Synchronization of ovulation after the 2nd injection is apparently precise enough to allow for a single timed insemination. Both injection of estradiol benzoate and GnRH [gonadotropin-releasing hormone] after PGF2.alpha. treatment will synchronize occurrence of estrus and the preovulatory surge of LH [luteinizing hormone], respectively. GnRH treatment at 48 h lowers the frequency of PGF2.alpha. induced heats, possibly due to alterations in plasma progestins and estradiol.