Influence of the ruminal N-balance on rumen metabolism

Fistulated dairy cows were used to investigate the influence of the ruminal N-balance (RNB) on protein metabolism in the rumen. Animals were fed a ration of maize silage and concentrates. RNB amounted to -0.6 g/MJ ME in the basis ration. The other 3 rations were adjusted to RNB-values of -0.3, 0 and 0.3 g/MJ ME by urea supplements. The RNB increase resulted in higher NH3-N concentrations in the rumen fluid and the duodenal digesta and urea concentrations in the milk and blood. The efficiency of microbial protein (MP) synthesis was the same, g MP/MJ ME was significant lower with RNB -0.6 g/MJ ME as compared to RNB 0. The group with the lowest RNB showed the highest level of feed protein degradation and the lowest organic matter fermentation.