chapter  19
26 Pages

of Technology to Improve the Calf Crop

Introduction............................................................................................................256 The Pattern of Return of Fertility Postpartum......................................................257 Early Embryonic Death Associated with Short Duration of the Luteal Phase: Lessons from the Postpartum Cow .....................................259 Follicular and Hormonal Patterns in the Preovulatory Period .............................263 Sources of Variation in Wave Patterns of Follicular Development ......................265 How Do Persistent Follicles Cause Low Fertility?...............................................266 Role of Follicular Secretion of Estradiol in Embryonic Mortality during Maternal Recognition of Pregnancy ..........................................................267 Late Embryonic Mortality: The Peri-Attachment Period .....................................268 Implications............................................................................................................272 References..............................................................................................................273

Luteal progesterone is essential for the preparation of the uterus and oocyte before breeding, as well as for the maintenance of uterine quiescence and the embryo/fetus during most of gestation in the cow. Prior to and immediately after estrus, progesterone regulates the mechanisms necessary for maternal recognition of pregnancy. Cows in which short estrous cycles (short luteal phases) were produced by early weaning (day 30 postpartum) or normal estrous cycles were produced by pretreatment with progestogen before early weaning have been used to elucidate specific points at which fertility is compromised in the early postpartum beef cow.