Effect of pregnant mare serum gonadotrophin (PMS) on ovarian function of beef heifers, as influenced by progestins, plane of nutrition, and fasting

Abstract

Beef heifers aged 1-3 years were kept on different planes of nutrition and given progestins to synchronize ovarian cycles. Treatments included fasting for 24 or 72 hr and/or administration of PMS 0 or 4 days, before the end of the synchronization regime. Ovulations and follicles greater than 3 mm in diameter were recorded at laparotomy and slaughter. Plane of nutrition, fasting, progestin treatment, time of year, and the dose and time of injection of PMS influenced follicular development and ovulation in PMStreated heifers. PMS given before the end of the progestin regime resulted in ovulation of a high proportion of follicles. The results are discussed in relation to design of experiments concerned with understanding the physiological basis of control of ovarian function in the cow.