The Fermentation of Carbohydrates in the Rumen of the Sheep

ABSTRACT Acetic, propionic and butyric acids are the main volatile fatty acids in the rumen of the sheep. Acetic acid accounts for 55 –75 % of the total. Cellulose, glucose and lactic acid are rapidly fermented in vitro by rumen contents with the production of acetic, propionic and butyric acids. Propionic acid is the major component in all cases : very little if any butyric acid is formed from cellulose. The in vitro fermentation of glucose closely resembles the in vivo. The in vitro fermentation of dried grass yields the same three acids, but with acetic acid predominating. Members of the genus Propionibacterium have been isolated from the rumen, and evidence is presented to show that these organisms are responsible for the production of the propionic acid found in the rumen. The dietary history of the animal is shown to influence the rate at which glucose is fermented in the rumen, and the composition of the rumen microflora.