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Reassessment of Efficiency of Synthesis of Microbial Matter in the Rumen

The Hannah Research Institute, Ayr, Scotland KA6 5HL

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 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 has been 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.

Numerous attempts have been made to measure the rate of synthesis of microbial matter in the rumen. There is agreement (26, 27, 33, 34, 37) in reviews that rates of microbial synthesis are variable and depend greatly on conditions.