Measurement of the rates of production of acetic, propionic and butyric acids in the rumen of sheep

Numerous studies have been made of the quantitative aspects of the production of volatile fatty acids (VFA) in the rumen, and have been reviewed by Rook (1964), Interest in rumen VFA production has recently been intensified because of the findings correlating body-weight increases with the concentration of rumen VFA in lambs on various pastures (Johns, Ulyatt & Glenday, 1963 ; Rae, Brougham, Glenday & Butler, 1963). Lambs grazing pasture supporting the greatest rate of growth had the greatest concentration of VFA in the rumen and also the highest proportions of propionate and butyrate to acetate. It is still not known, however, whether organic acid levels in the rumen are indicative of production or absorption rates since concentrations of individual acids in the rumen are a balance between production, absorption, passage along the intestinal tract and conversion into other compounds.