Negative correlation between protozoal and bacterial levels in rumen samples and its relation to the determination of dietary effects on the rumen microbial population.

The bacterial protein content and protozoal protein content of unfractionated samples from the liquid-small particle phase of the rumen were determined on the basis of direct microscopic measurement of bacteria numbers and protozoa numbers and cell volumes. Standard values of 8.7 X 10(-11) mg of protein per bacterial cell and 5.9 X 10(-11) mg/micron 3 of protozoa cell volume, obtained from analysis of isolated cells, were used to convert the microscopic measurements to an estimate of the protein content of the rumen sample. When the correlation between bacterial and protozoal protein levels was examined within groups of animals, a highly significant negative correlation between these two parameters was found (P less than 0.001). The variation among animals for total (bacterial plus protozoal) microbial protein was smaller than the variation among animals for bacterial or protozoal protein alone. There was also a highly significant positive correlation (P less than 0.001) between protozoal protein level and total microbial protein level. The variation found among animals in total microbial protein level could be reduced by using a regression equation determined for bacterial versus protozoal protein to correct for the different population dynamics of the two groups.