ABSORPTION OF STEAM-VOLATILE FATTY ACIDS FROM THE RUMEN OF THE COW AS INFLUENCED BY DIET, BUFFERS, AND pH

Abstract

Observations were made on the absorption of steam-volatile fatty acids from the temporarily isolated, washed ventral sac of the rumen of the conscious cow. At pH 7.0, absorption of fatty acids from a 50-mM bicarbonate buffer was similar to that obtained with a 40-mM phosphate buffer. With higher levels of phosphate (75 mM) and bicarbonate (90 mM) at pH 7.0, fatty acid absorption appeared to be lower from the bicarbonate buffer. When cows were fed a high concentrate diet, absorption of fatty acids was more rapid than when the diet had been all hay. Lowering the pH of experimental solutions increased fatty acid absorption. Clearance (amount absorbed divided by the fatty acid concentration) of fatty acids increased progressively with increasing chain length of the acids as the pH dropped below 7. Taking acetate clearance as 1.0, the clearance of propionate and butyrate, respectively, were 1.1 and 1.0 at pH 7.0; 1.2 and 1.4 at pH 6.5; and 1.6 and 2.4 at pH 5.5. Varying acetate and propionate concentrations did not influence the clearance of the fatty acids.