Alteration of Ovarian Activity in Cycling, Pregnant and Hysterectomized Heifers with Exogenous Estrogens

Embryonic mortality is an important factor limiting reproductive performance in cattle. A large proportion of the embryonic loss occurs between 17 and 21 days of gestation. This coincides with a decrease in progesterone production by the corpus luteum beginning on day 14 or 15 in the cycling and pregnant cow. The purpose of this study was to determine the effects of different forms of estrogen on ovarian function in the cycling, pregnant and hysterectomized beef heifer. Ninety-nine yearling Hereford heifers were used in a 5 x 3 factorial experiment to study the effects of various estrogens on ovarian activity. The heifers were randomly assigned to a cycling, pregnant or hysterectomized group and to one of three hormone treatments within each group. Advisor: D. R. Zimmerma