Submitted to: Brazilian Animal Science Society
Publication Type: Proceedings
Publication Acceptance Date: July 26, 1999
Publication Date: N/A
Interpretive Summary: This is a review paper. No Interpretive Summary Required.
Technical Abstract: To maintain a cow herd, a fraction of the cows must be replaced each year with younger females. Biological and economic efficiency of raising replacement females typically follows a quadratic response. As inputs increase, output is increased; however, the return per unit input becomes a smaller proportion. The profitability of a production system depends on providing the required inputs without exceeding the requirements. Exceeding requirements increases production cost while not meeting requirements reduces output. The quality of a replacement heifer is both a function of her genetic potential and her experiences during development. The most common cause for reproductive failure in the heifer or young cow is poorly timed nutrition. This poor nutrition can either be excessive or insufficient nutrition. In most grass-based production systems, nutrient availability is rarely excessive; rather, nutrient availability generally limits expression of the animal's genetic potential. Appropriateness of the breed type for a forage system will dictate the supplementation strategy required. We have some general cause-and-effect relationships that are known to influence the quality of the replacement female, but the ability to put these relationships into practice is limited by the general lack of data on nutrition by genotype interactions. Much of the research on the effect of nutrition on reproductive fitness has not been experimentally designed to allow the animals to fail. This lack of data on the effects of very low nutrition on reproduction makes it difficult to predict whether the behavior of the response curves are thresholds or are continuous. Future studies should investigate those response behaviors.