Quantification and chemical composition of mixed bacteria harvested from solid fractions of rumen digesta: effect of detachment procedure

Four ewes were given two diets made up with two ratios of rolled barley grain and ammonia treated straw (80/20, diet C and 20/80 diet R) twice a day. Two microbial markers, purine bases (PB) and 15N, were used as internal and external markers, respectively. Ruminal bacteria from the liquid (LAB) and solid (SAB) fractions of digesta were harvested from samples obtained at 1 and 6 h after feeding. Bacteria were separated from the particulate material by cooling plus homogenisation (B) and also by applying tertiary butanol (TB), methylcellulose (M) or changes of temperature (CHT). The most effective procedures to remove bacteria from the solid phase were M and CHT although CHT showed the highest level of losses and the lowest total recovery of the bacterial pellet. There were no differences between B and TB in both detaching efficiency and total recovery ratio of adherent bacteria. Ratio of recovery of detached material as a bacterial pellet was 32.0, 32.2, 33.3 and 27.8% for B, TB, M and CHT, respectively. Diet did not interact with detaching efficiency of the experimental treatment although concentration of total N (g/100 g OM) and PB (μmol/g OM) content concentration were higher in pellets obtained with diet C (9.11 and 125) than with R (8.20 and 107, respectively, P<0.05). Postprandial differences were not significant. Bacterial samples extracted from the liquid phase contained significantly (P<0.001) more total N (9.21 vs. 8.51) PB (160.5 vs. 104.3) and PB/N (1.73 vs. 1.23 μmol/mg) than those samples extracted from the solid phase. There were no differences in the chemical composition of the microbial sample after detachment by B, BT and M but bacterial extract obtained after CHT treatment showed significant changes in PB, N content and PB/N ratio (P<0.01).