The buffering capacity of caecal digesta exceeds that of rumen digesta from sheep fed pasture or roughage diets

Abstract

The buffering capacities of caecal and rumen digesta of sheep on different diets were determined by titration with lactic, acetic, and hydrochloric acids, and certain factors affecting the buffering capacity of rumen digesta were studied. Both rumen and caecal digesta had maximal buffering capacity at pH 6·5–6·0. The buffering capacity of caecal digesta was nearly double (P < 0·001) that of rumen digesta. The rumen digesta from sheep fed oaten chaff had a buffering capacity 21% higher (P < 0·05) than that of sheep grazing green pasture. This was reduced (P < 0·05) by one-third following ruminal infusions of glucose, lactic, or acetic acid to induce acidosis. Diet did not significantly affect the buffering capacities of rumen and caecal digesta. However, the buffering capacities of rumen and caecal digesta from pasture-fed sheep that had been fasted for 24 h were significantly greater (P < 0·001) than those for sheep that had not been fasted (62 and 18%). The buffering capacity determined using HCl was always less than that for lactic or acetic acid. This may be due to the lower pKa for HCl and the fact that there is no evidence that HCl undergoes inter-conversion through fermentation that the organic acids may undergo. The addition of carbonate or phosphate buffer significantly increased (P < 0·05) the buffering capacity of rumen and caecal digesta. The sodium bicarbonate and sodium carbonate (NaHCO3 and Na2CO3) system played a more effective buffering role than the sodium dihydrogen orthophosphate and disodium hydrogen orthophosphate (NaH2PO4 and Na2HPO4) system in the rumen digesta.