Effect of variation in the proportion of solid- and liquid-associated rumen bacteria in duodenal contents on the estimation of duodenal bacterial nitrogen flow

The aim of this research was to examine to what extent variation in the relative proportions of solid- (SAB) and liquid-associated rumen bacteria (LAB) in duodenal bacteria have an impact on the estimation of duodenal flowofbacterialN.Forthis,fourdairycowswerefeddietsvaryinginforage:concentrate ratio (80:20, 65:35, 50:50 and 35:65). SAB and LAB were separated from rumen contents four h after the morning feeding. Adenine, cytosine and odd and branched-chain fatty acids were determined both in SAB and LAB and used to estimate bacterial N flow. Bacterial N flowswerealsocalculated using a SAB:LAB ratio in duodenal bacteria, as estimated from the odd and branched-chain fatty acid pattern. Compared with calculations based on the estimated SAB:LAB ratio, estimations based on SAB or LAB only as a bacterial reference on average over- and underestimated bacterial N flowby37and55gN/d,respectively(P