Estimation of Rumen Microbial Nitrogen by Three Analytical Methods

Perchloric acid-soluble residue, tungstic acid precipitate, and separatory funnel techniques were evaluated by comparing results of microbial cell dry matter, per cent nitrogen, and total nitrogen in rumen samples before and after feeding. Significantly less (P 0.01) cellular dry matter remained in perchloric acid samples than with other methods due to procedural complications in washing and decanting specimens. As a result of incomplete separation by the separatory funnel techniques, per cent nitrogen in the dried microorganisms was significantly reduced (P 0.01); however, microbial preparations by the separatory funnel method contained less (P 0.10) feed contamination than nonseparatory funnel procedures. The tungstic acid method consistently yielded significantly greater (P 0.01) amounts of total nitrogen from the rumen microbial samples, suggesting that limitations in the other methods were of importance in quantitative analyses.