Reproductive physiological responses of cattle to exogenous prostaglandin F2alpha

Prostaglandin F2alpha caused rapid regression of the corpus luteum and initiated normal transitory hormonal patterns that culiminated in ovulation. PGF2alpha was effective in heat stressed heifers and a thermal stress of 32 C caused no major hormonal alterations from the time of CL regression to ovulation. A luteolytic dose of PGF2alpha tham salt (33.5 mg) given intramuscularly caused no major alterations in blood pressure, heart rate, and uterine or aortic blood temperatures. However, the same dose given as an intravenous jugular infusion over a 2 min period caused major alterations in circulatory homeostasis and body temperature. Treatment of all cattle twice with PGF2alpha tham salt (33.5 mg), 12 days apart, increased the number of responsive heifers at the second PGF2alpha injection. Synchronization of ovulation after the second injection is apparently precise enough to allow for a single timed insemination. Blood injection of estradiol benzoate and GnRH after PGF2alpha treatment will synchronize occurrence of estrus and the preovulatory surge of LH, respectively. However, GnRH treatment at 48 h lowers the frequency of PGF2alpha induced heats and this may be due to alterations in plasma progestins and estradiol.