ABSTRACT
The dam completes the hormonal process begun by the fetus; this involves a rise in the estrogens, a drop in progesterone, peak production of prostaglandin levels just prior to giving birth, and the release of oxytocin prior to and during the birth process. The cow depends on a corpus luteum (CL) to maintain pregnancy. Conversely, the destruction of that CL is necessary to terminate that pregnancy during the birth process. Calf birth weight is the most important factor to consider in this type of dystocia. Calf birth weight is a moderately heritable trait and basically is a function of the calf's genetic capacity, with maternal environment accounting for a small part. Reduction of the prepartum energy intake of cows can increase the time from birth to subsequent cycling and rebreeding of the cows. The Simmental association has shown that some of its sires produce calves with birth weights below average for the breed yet have superior yearling weights.
