Evaluating the predictive ability of a mechanistic model of nitrogen partitioning applied to lactating dairy cows consuming ryegrass-based diets

摘要

The ability to understand and predict ruminant nitrogen (N) partitioning has become important as concerns over the environmental impact of pastoral agriculture increase. A mechanistic model of N partitioning from dairy cows consuming ryegrass was usedto quantify the amount of N secreted in milk, urine, and faeces, and retained in body tissues. Data from lactating dairy cows (13 N balance experiments) were used to evaluate the model. Predictions for milk, urinary, faecal, and total excreta N were inagreement with observed values. Empirical models have been successful in predicting N partitioning from ruminants, but such approaches lack the underlying biological processes and may not apply to all observed values. An improved representation of the underlying mechanisms of N partitioning and the possibility of identifying areas where knowledge is lacking was achieved by the use of the current mechanistic model.