EFFECT OF DIET AND PROBIOTIC ADDITION ON CHEMICAL-COMPOSITION OF FREEOR PARTICLE-ASSOCIATED BACTERIAL-POPULATIONS OF THE RUMEN

Eight dairy heifers (297 +/- 11 kg) fitted with a ruminal cannula were used in this study. The following diets were fed in a replicated, con currently run 4 x 4 Latin square design: 1) 80% chopped timothy hay 20% rolled barley (HF); 2) HF + 10 g head d(-1) of a mixture of Saccha romyces cerevisiae and Aspergillus oryzae (HF + SA); 3) 50% chopped ti mothy hay + 47.6% rolled barley and 2.4% soya supplement (HC); 4) HC SA. Feed was offered every 2 h. A sample of whole rumen contents (liq uid and solid) was collected 1 h after the 07:00 h feeding to isolate the bacteria associated with the liquid phase (BAL) and the bacteria a dherent to the solid phase (BAS). Organic matter (OM) content of BAS w as greater (P less than or equal to 0.0001) than that of BAL, independ ently of the type of diet fed and of the presence or absence of the pr obiotic mixture. Oppositely, total nitrogen content (N), expressed as g 100 g(-1) OM, was greater (P I 0.0001) in the BAL fraction than in t he BAS fraction, the difference in N between the two bacterial fractio ns being more pronounced with the HF diet (P less than or equal to 0.0 5). Organic matter content in both bacterial fractions was greater (P less than or equal to 0.05) when heifers were fed the HC diet. Additio n of probiotic had no effect on OM or N content of each bacterial frac tion. Significant differences between amino acid composition of BAL an d BAS were observed for 10 out of 16 amino acids studied. For most ami no acids, differences in content observed between BAL and BAS were mai ntained independently of the probiotic supplementation whereas diet af fected the relative composition of the bacterial fractions for five am ino acids. Finally, addition of probiotics did not affect molar propor tions of ruminal volatile fatty acids, which were affected by the diet .