Natural 15N abundances in plasma and urea-N concentration in milk as biomarkers of urinary N excretion in dairy cows: a meta-analysis

摘要

Knowledge on the flux of nitrogen (N) excreted through urines is essential in animal nutrition since it may provide information on animal N metabolism and the extent of environmental N pollution. Both the 15N natural enrichment of animal proteins overthe diet (A15Nanima _diet) and the milk urea-N (MUN) concentration have been previously linked to N partitioning. The objective of this metaanalysis was to test the effect of combination of A15N toal_diet in plasma and MUN for predicting the urinary N excretion (UNE) in dairy cows. Individual data on A15Nanima_diet in plasma, MUN, and UNE of 177 cow/period observations were evaluated by meta-analysis. Data were analyzed by mixed-model regression analysis. When model was fitted with either A15N.mal_dietor MUN, both biomarkers were capable to independently predict UNE. However, when A'^N im _diel and MUN were combined in one model, both biomarkers remained significant and the error of the model slightly decreased. In conclusion, both A15Nanima_diet andMUN can predict UNE and their combination can strengthen the prediction capacity of the model.