An important factor in the production of waste Nitrogen (N) and Phosphorus (P) by cows is the amount of these elements supplied in the diet. Supplying N and P at levels higher than the requirement for maintenance and production will result in the excess being excreted in faeces and urine causing an increased load of environmental pollutants, with ensuing problems for nitrate concentrations in ground water or P concentrations in surface run off water. Appropriate diet formulation should allow a higher level of nutrient capture as milk or tissue, whilst minimising losses in urine and faeces.