REASSESSING THE MANIPULATION OF PROTEIN-SYNTHESIS BY RUMEN MICROBES

Protein synthesis by rumen microbes plays an important role in ruminan t nutrition. Microbial proteins that are not recycled flow out of the rumen and account for more than 50% of the total proteins entering the intestines. Determination of microbial nitrogen in digesta is based o n the isolation of a representative sample of rumen microbes and on th e use of specific markers (purine bases, RNA, N-15 incorporation). Thi s review discusses the reliability of microbial markers and examines c urrent methods for assessing differences in turnover rate and microbia l composition among liquid and particulate compartments. Four groups o f factors acting on microbial synthesis, which are also adaptable to f arm conditions, are considered: I) modification of protozoal populatio n; II) modification of liquid and solid phase kinetics in the rumen; I II) balance in the components of the diet; and IV) probiotics. The eff ects of these factors are discussed, considering their feasibility and their usefulness for the host.