Quantitative estimation of net rates of production of bacterial and protozoal nitrogen and their interconversion in the rumen

A technique is described using 35S-labelled bacteria or protozoa by which the rates of production of microbial and protozoal protein N may be calculated. The results indicate an average microbial protein yield of about 13.7gN.d-1 in sheep maintained on a diet consisting largely of cottonseed cake and wheat and rice bran. Evidence is presented that protozoa made little contribution to the microbial protein-N leaving the rumen. Also, the average rate of N flow from the protozoal to the bacterial pool was about 3.5g.d-1, whereas about 1.4g.d-1 of bacterial N was consumed by protozoa. (author)