COMPOSITION OF LIQUID-ASSOCIATED AND PARTICLE-ASSOCIATED BACTERIA ANDTHEIR CONTRIBUTION TO THE RUMEN OUTFLOW

A method is described to estimate the composition and rumen outflow of microbes associated with liquid (LAB) and solid (SAB) digesta. Four r umen-cannulated Rasa Aragonesa ewes were given, in random order, the f ollowing 4 diets: (II) NaOH-treated barley straw, as a sole diet (700 g/day, TS); (2) NaOH-treated barley straw mixed (50:50) with 400 g/day of rolled barley grain (BS); (3) Diet I with addition of 8 g/day of u rea; and (4) Diet 2 with addition of 16 g/day of urea. Co-EDTA was use d as a marker for the liquid phase to estimate rumen outflow of liquid -associated purine bases (PB), and urinary purine derivatives were use d as an indirect marker of total duodenal flow of PB. Solid-associated PB were calculated by the difference between both estimates. Urea inf usion increased ammonia-N concentration in the rumen fluid from 4.8 to 15.9 mg/100 mt (P < 0.05) and enhanced dry matter intake of TS diets (from 343+/-63.5 to 556+/-41.2 g/day, P < 0.001). Significant differen ces were observed in the PB/N ratio of bacteria harvested from the liq uid phase compared with that isolated from the solid phase (1.89+/-0.2 5 v. 1.66+/-0.32 mol/mg in LAB and SAB, respectively). Because of the differences observed between the liquid and solid-associated bacteria, estimated values of bacterial N supply varied depending on which bact erial extract was used as reference. The fractional contribution of LA B and SAB to the postruminal bacteria was significantly influenced by the experimental diets, mainly through variations in the amount of LAB flowing out of the rumen.