showed that feeding the 18.8% CP diets, 44% of the N excreted was excreted as urine and milk urea compared with 38% with the 16.1% CP diets. This increases milk production costs plus environmental N pollution. Moreover, there was no further improvement in milk fat content and feed efficiency beyond 16% CP (P > 0.05) and dietary CPnot utilised for production is lost in the urine, the most polluting form of excretory N