Production and Absorption of Volatile Fatty Acids in the Perfused Rumen

Abstract

Summary The rumens from three mature goats were perfused with homologous heparinized blood to measure the rate of volatile fatty acid (VFA) production and absorption. An effort was made to maintain an active microbial population and fermentation during the perfusion by approximating normal conditions with respect to anaerobiosis, temperature, substrate, and removing the end products of fermentation. Volatile fatty acid absorption rates were much below expected values, which may be attributed to a slow rate of blood flow. The average blood flow rate for the three perfusions was 17 ml/min. The inability to remove the fatty acids from the rumen via absorption may have affected the production rates which were: acetic, 2.61 g/hr; propionic, 1.16 g/hr; and butyric, 0.89 g/hr. In contrast to reports in the literature, the relative proportions of VFA's in the rumen vein blood (A,51; P,26; B,23) were nearly identical to those in the rumen fluid (A,55; P,22; B,23). Glucose utilization by rumen tissue was demonstrated by arteriovenous differences of 6–10mg.%. Low levels of ketone bodies were observed in venous blood. Three other perfusions were conducted to study the effect of radical changes in the proportions of the VFA's in the rumen on the distribution of these acids in the perfusate. The addition of either propionic or butyric acids, which shifted the ratio of the acids in the rumen field, caused drastic changes in proportions of these acids in the rumen vein blood. Although blood VFA ratios did not show a linear relationship to the ratios observed in the rumen fluid, it was apparent that the acids were absorbed at rates depending on their concentration in the rumen. The addition of butyric acid to the perfused rumen brought about increases in ketone body levels in the venous blood. Ketone body production by the rumen tissue may be of importance under conditions where high levels of butyric acid are present in the rumen.