Reproductive Steroids in the Bovine. III. Changes during the Estrous Cycle

Abstract

A Recent review shows that cyclic changes during the estrous cycle of cows, ewes and sows are indicated by day-to-day variations in weight and progesterone content of corpora lutea (CL) and levels of progesterone in ovarian venous and peripheral blood plasma (Erb, Randel and Callahan, 1971). Moreover, changes in rate of excretion of metabolites of progesterone in urine of sows during the estrous cycle reflects the cyclic variations in levels of progesterone in ovarian venous (Schomberg et al., 1966) and peripheral blood plasma (Tillson, Erb and Niswender, 1970). Concentrations of luteinizing hormone (LH.) in peripheral blood plasma of the nonpregnant cow increase to a distinct peak 15 to 22 hr. prior to ovulation (Schams and Karg, 1969) or 3 to 6 hr. after the onset of estrus (Henricks. Dickey and Niswender, 1970). During the estrous cycle in sows, plasma progesterone and LH are negatively correlated (Tillson et al., 1970) and in ewes plasma progesterone is positively correlated to urinary estrone and negatively correlated to urinary estradiol (Plotka. Erb and Harrington, 1970). Copyright © 1971. American Society of Animal Science . Copyright 1971 by American Society of Animal Science.