A model to predict nitrogen excretion from dairy cattle using the PDI protein system

Introduction There is increased pressure on agriculture to reduce nitrogen (N) excretion from different production systems. In order to do so, it is of value to know how diets compare in terms of N excretion, as this could have both financial and environmental consequences. A mechanistic model describing the N digestion and metabolism in ruminants was developed from the PDI protein system to enable this comparison. The aims of the exercise were to develop a model that predicts the N excretion in urine and faeces of dairy and beef cattle, and to relate model predicted faecal and urinary N excretion to experimentally measured faecal and experimentally estimated urinary N excretion from grazing dairy cows.