The Absorption of Volatile Fatty Acids from the Rumen

1. When a dilute solution of the sodium salts of acetic, propionic and butyric acids was introduced into an empty rumen no significant change was observed in the relative proportions of the acids present, within a 6 hr. period. 2. When a similar mixture was introduced, and the animal ate lucerne during the experiment, marked changes occurred in the proportion of the acids present, indicating a more rapid absorption of propionic acid than of the other acids. 3. A similar absorption was observed on introducing a solution of the sodium salts of acetic and propionic acid, at pH 6.5, containing an amount of inorganic phosphorus equivalent to that occurring in sheep's saliva. By the inclusion of pectin as an unabsorbed reference substance in such a mixture it was shown that a considerable dilution of the rumen contents occurred during the experiment--presumably by the advent of saliva. The relative rates of absorption of acetic and propionic acids were determined over particular ranges of acid concentrations. 4. On the basis of the relative rates of absorption of these acids at concentrations in which they were found to occur in the normal rumen during the fermentation of wheaten-hay chaff, it was concluded that a much greater proportion of propionic acid is formed than is indicated by analyses of the acids found in the rumen.