Two bulls with a permanant rumen fistula and a re‐entrant cannula at the duodenum were fed various concentrates and straw (dry matter ration composition: 60% concentrate, 40% straw). Negative correlations were found between the pH value and total fatty acid concentration (r= ‐0,70). The animals were given the straw one hour before the concentrate. The pH value increased to not more than 7.3 one hour after they had received the straw. It did not drop below 6.4 after the concentrate with any of the rations. The addition of dried sugar beet pulp to the rations leads to a higher mean acetate concentration than the other rations and causes an unvarying high total fatty acid concentration.