Manipulation of rumen fluid pH and its influence on cellulolysis in sacco, dry matter degradation and the rumen microflora of sheep offered either hay or concentrate

1. (1) It was possible to alter and maintain the rumen pH of three sheep given hay and three given concentrate by the continuous infusion of various amounts of an acid solution (H 2SO 4:HCl:H 2PO 4; 1:1:1, w/w) and a bicarbonate solution (NaHCO 3 (66%):KHCO 3 (34%), w/w), respectively. 2. (2) Reduction of the rumen pH (to 6.0–6.1) in sheep given roughage led to the inhibition of cellulolysis and partial destruction and washout of the rumen microflora. Dry matter degradation in the rumen and dry matter intake were also depressed. 3. (3) Increasing the rumen pH of sheep offered the concentrate diet did not greatly alter the rumen microflora nor did it increase cellulolysis, dry matter degradation or dry matter intake. 4. (4) It appears that both the type of substrate present in the rumen and the rumen pH have important effects on ruminal cellulolytic activity.