Composition of bacteria harvested from the liquid and solid fractions of the rumen of sheep as influenced by feed intake

A study was conducted to determine the effect of the feed intake on the che mical composition of bacteria associated with the solid (solid-associated b acteria; SAB) and liquid (liquid-associated bacteria; LAB) fractions of rum en digesta, the digestive passage kinetics and their relationships. Whole r umen contents were sampled after a period of continuous infusion of (NH3)-N -15 from four ruminally-cannulated wethers provided successively with a hay -concentrate diet (2: 1 w/w on a DM basis) at two rates of feed intake: 40 and 80 g DM/kg body weight(0 . 75). SAB had a higher content of organic mat ter and total lipids (P < 0 . 001) and a similar N content as compared with LAB. The concentration of purines and N-15 was lower (P = 0 . 011 and P < 0 . 001 respectively) in SAB than LAB, whereas the opposite was observed fo r the concentration of amino acids (mg/g DM; P = 0 . 031). An increase in f eed intake produced an increase in the N (P = 0 . 034) and purine (P = 0 . 066) concentrations in bacteria and a decrease (P = 0 . 033) in their amino acid concentrations. Significant increases of rumen outflow rates of liqui d and particles were also observed with increased feed intake. Rates of rum en outflow showed positive and negative linear relationships (P < 0 . 001) with the purine:N ratio and the proportion of amino acid on total N of bact eria respectively. SAB contained significantly higher proportions of leucin e, isoleucine, lysine and phenylalanine and lower proportions of alanine, m ethionine and valine than LAB. The increase in feed intake also induced sig nificant changes in the amino acid profile of bacteria, increasing arginine and methionine and decreasing alanine and glycine proportions. Results sho w that the outflow rate of rumen contents is a major factor in determining the proportion of nucleic acids and protein in lumen bacteria and explains some of the differences observed between LAB and SAB.