Gas and Volatile Fatty Acid Production at Different Rates of Rumen Microbial Protein Synthesis In Vitro

Two Merino sheep with rumen fistulae were used as sources of rumen contents. The animals were fed a protein-free diet with urea as the sole source of nitrogen. Microbial protein in rumen contents was determined by precipitation with trichloroacetic acid (TCA -- N). Microbial growth and both gas and volatile fatty acid production were determined in in vitro 1-hr incubations. In some experiments, end product formation continued as a relatively constant rate even though TCA-N was decreasing due to lysis. Negative relationships were generally obtained between microbial growth and end products formed. These relationships were greatly affected by the velocity of microbial growth and the environmental conditions applied. The present data indicate that no constant relationship exists in vitro between microbial protein synthesis and end product formation.