Relationship between content of crude protein in rations for dairy cows, N in urine and ammonia release

This paper discusses the outcomes of experiments investigating the influence of the content of crude protein (CP) in dairy cow diets on nitrogen in urine and ammonia release. It compares different concepts to calculate nitrogen in urine from nitrogen intake, both from a simulation model or equations based on nitrogen intake or feed parameters such as AAT and protein balance value (PBV). The simulation model could predict the outcome roughly but, however, underestimated the milk production in alternatives with a low level of CP. This might be due to an underestimation of the microbial rumen production in these alternatives, when diets had a higher ration of super-pressed beet pulp, which has a high content of easily fermented carbohydrates. The most accurate prediction of nitrogen in urine was made by an equation based on AAT, PBV and nitrogen in milk. Ammonia release can be tripled when %CP increases from approximately 13-19%. Prediction of ammonia was more exact from CP than from N in urine, due to the effect of urine volume on the actual amount of release. (C) 2003 Elsevier B.V. All rights reserved.