Numbers and characteristics of lactate-utilizing organisms in the rumen of cattle.

Elsden (1945) has shown that the volatile acids in the rumen fluid of sheep are chiefly acetic, propionic, and butyric. Barcroft, MoAnally, and Phillipson (1944) showed that the concentration of volatile acids in the blood draining the rumen was higher than that in the entering blood, indicating absorption from the rumen. Elsden postulated that propionic acid did not arise directly in cellulose fermentation in the rumen but was derived from lactic acid. In agreement with this view Hungate (1950) has found formic, acetic, and butyric acids, but no propionic acid, produced from cellulose by pure cultures of bacteria isolated from the rumen. Elsden (1945) cultured an unidentified noncellulolytic gram positive coccus from the rumen of sheep which was assigned to the genus Propionibacterium and which produced propionic acid, acetic acid, and C02 from lactate. The numbers of these organisms were not determined. From New Zealand, Johns (1951) has reported an anaerobic gram negative coccus, Veillonella gaogene8, isolated from the rumen of sheep, which produces propionic and acetic acids, hydrogen, and carbon dioxide. It occurred in numbers of about one million per ml and rapidly attacked succinic acid, forming propionic acid and carbon dioxide. In the present study an attempt has been made to obtain more information on the lactate utilizing bacteria in the rumen of cattle by determining the kinds and numbers present.