Rumen microbial protein synthesis in relation to energy supply: Diurnal variation with once-daily feeding

Abstract

Rates of microbial protein synthesis and volatile fatty acid (VFA) production were measured in sheep rumen contents collected at 4-hr intervals after a single feed consisting of chaffed lucerne and wheaten hay. The protein synthesis rate observed was minimal at 4 hr after cessation of feeding, rising to a maximum 8 hr later. Protein synthesis in relation to energy supply (calculated from VFA production) was also minimal 4 hr after cessation of feeding, but did not reach a maximum until 16 hr later. Decreasing utilization of energy for protein synthesis was correlated with an increase in the polysaccharide content of the microbial cells, and a return of cellular polysaccharide levels to the pre-feeding values was accompanied by increased usage of energy for protein synthesis. The results are discussed in terms of alternative mechanisms for energy utilization at different times after feeding, and of overall microbial protein synthesis in relation to organic matter digested in the rumen.