Prediction of nitrogen efficiency in dairy cattle: a review.

Abstract

Abstract Increasing the efficiency of conversion of feed nitrogen (N) into milk and meat N in dairy cattle is an integral part of the effort to maintain or increase food production while decreasing agriculture's environmental impact. Mathematical models provide a means to assess and compare different strategies to increase N efficiency; however, their merit depends on the models' predictive capabilities. Evaluation of the currently available empirical models to predict faecal and urinary N excretion revealed low prediction accuracy and the presence of significant systematic biases. Application of more diverse and advanced model development techniques are needed to produce models whose precision and accuracy are sufficient for application in emissions mitigation protocols. Mechanistic models continue to advance and push the boundaries of knowledge in ruminant N metabolism; aided by advances in computer technology. However, improvement is required in the description of factors that influence microbial protein production and the use of metabolizable protein; this represents the greatest potential for increasing our prediction and understanding of N efficiency in dairy cattle. Attention to these two aspects of ruminant N metabolism in mechanistic models directed specifically at improving N efficiency and in the widely used nutrient requirement models will enhance our ability to meet dairy cattle's protein requirements in a sustainable manner.