Estimation of the duodenal flow of microbial nitrogen in ruminants based on the chemical composition of forages: a literature review

Abstract

The objective of this study was to evaluate the estimation of the duodenal flow of micro- bial nitrogen (N) in ruminants fed forage only, per kilogram of dry matter (DM) intake, which is the yield of microbial protein (YMP). The estimation was based on the chemical composition of forages. A data file of 62 observations was collected from in vivo studies on cattle and sheep fed diets with for- age only. A statistical analysis of YMP was conducted with neutral detergent fibre (NDF), crude pro- tein (CP), non structural carbohydrates (NSC), group of forage species (legumes or grasses), method of conservation, physical form of presentation, level of DM intake, animal species, methodology and references as parameters. After a stepwise regression, CP was significant and the most important pre- dictor. NSC or the method of conservation had an extra effect on YMP. On the basis of these three pa- rameters the best fit equations were found and the influence of all parameters on YMP were discussed. Using the data file of this study, the prediction of YMP from the PDI-system was also vali- dated. The statistics of the validation of the PDI prediction were similar to the statistics of the equa- tions from this study. In conclusion, the chemical composition of forages, with or without the method of conservation, is a poor indication for the duodenal flow of microbial N (g·kg -1 DM intake) in ruminants fed diets with forages only.