Effects of centrifugation speed and freezing on composition of ruminal bacterial samples collected from defaunated sheep.

Triplicate ruminal samples from four rumen-cannulated defaunated sheep (50 kg BW) were used in a completely randomized design experiment with a 2 x 3 factorial arrangement of treatments to test effects of two pretreatments (fresh vs. freezing) and three centrifugation speeds (4640 x g for 30 min; 9820 x g for 20 min; 25,900 x g for 20 min) or quantity of ruminal bacteria harvested and composition of ruminal bacterial samples. There were no differences among centrifugation speeds on quantity of ruminal bacterial harvested, organic matter, total N, RNA, and diaminopimelic acid concentrations (% of DM), or RNA:N, RNA:organic matter, N:organic matter, and diaminopimelic acid:organic matter ratios. However, there were differences between fresh and frozen samples for all measurements except diaminopimelic acid concentration, and the diaminopimelic acid:organic matter ratio, suggesting that freezing ruminal fluid is not appropriate for obtaining truly representative bacterial samples.