Abstract
Published determinations of efficiency of synthesis of microbial matter, methods, and procedures for calculations were assessed critically. The generalized composition of microbial matter was calculated from results of analyses of microbial fractions from the rumen of animals [cows] under varied conditions. Terms to describe dissimilation of organic matter in the rumen were defined. Distinction was made between organic matter apparently digested but corrected for microbial matter entering the duodenum, organic matter truly digested and organic matter fermented. Equations were derived to show how these quantities and efficiencies calculated from them are interrelated. Attempted rationalizing results of 75 individual determinations reported in 25 papers by considering the microbial composition and method of calculating efficiency showed that efficiency of synthesis of microbial matter is less than was assumed. The theoretical efficiency obtained calculating it from the stoichiometry of rumen fermentation on the assumption that polyglucose (+ ammonia) is the sole substrate, showed that theoretical efficiency was similar to the mean overall efficiency calculated from published data.

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