A comparison of the mixtures of acetic, propionic and butyric acids in the rumen and in the blood leaving the rumen

Abstract

Absorption of acetic, propionic and butyric acids is known to occur from the rumen of sheep but some confusion concerning relative rates of absorption of these acids has arisen, for although it is agreed that free acids are absorbed more rapidly than their sodium salts when aqueous solutions are in the rumen (Danielli, Hitchcock, Marshall & Phillipson, 1945;Gray, 1947) it has been claimed recently that no absorption at all occurs from the rumen when the pH is over 7 (Gray, 1948).Under normal feeding conditions the pH of the contents of the rumen rarely falls below 5'5; for this reason the quantity of free acid present is small compared to the quantity of anion. Absorption, therefore, is likely to be insignificant if the membrane lining the rumen is permeable only to free acid. Further investigations, which are reported in this paper, were undertaken to compare the mixture of acids present in the rumen with the mixture present in the blood leaving the rumen, for this should show whether the mixture of acids present in the rumen is indicative of the mixture passing to the liver from this organ.The majority of these comparisons were made while two of us (R. A. M. and A. T. P.) were working in the Unit of Animal Physiology, Cambridge, whilst confirmation of these results using a different method of analysis was obtained at the Rowett Research Institute. METHODSExperimental. Normal ewes were taken straight from pasture to the laboratory. They were anaesthetized by intravenous injection of nembutal, the abdomen was opened on the right side and the posterior vein of the rumen was located as previously described (Barcroft, McAnally & Phillipson, 1944). In addition, the right carotid artery in the neck was exposed. The experimental procedure was usually as follows.After exposing the posterior vein of the rumen 5 ml. of blood were withdrawn from the carotid

Functional development of epithelial tissue of the reticulo-rumen in calves

“…Danlelll et al (1945), using the change in the concentration of VFA in the rumen contents as the criterion of absorption, found that the order of absorption of the three principal VFA was as suggested by Barcroft et al (1944a) when the rumen con tents were alkaline (pH 7.5)• However from rumen contents at a more acid reaction (pH 5.8) the higher homologues of the VFA were absorbed faster. Kiddle et al (1951) concluded that the higher homologues of the VFA were not absorbed prefer entially from rumen contents at an acid pH, but Gray et al (1951), Gray and Pilgrim (1951), Hungate et al (1961), Johnson (1951) and Pfander and Phillipson (1953) confirmed the conclusions of Danlelll et al (1945) and Gray (1947Gray ( , 1948.…”

“…The main weakness of the technique is that it is conducted in vitro : confirmation of the validity of these results by in vivo techniques is still required. However, the in vivo data of Kiddle et al (1951) This difference may have been due to a greater permeability of the epithelium of the MHG calves or to some quite different factor such as greater blood flow. If permeability of the membrane was the important factor In the absorption studies, the differences in metabolic activity of the two tissues could be ascribed to the inability of the substrate to reach the site of metabolism rather than to the lower metabolic activity of the cells.…”

“…Although the specific absorption rate 1 of acetate was slower than that of the other VFA, its total absorption usually exceeded that of the others since its rate of production was greatest (Hungate et al, 1961;Johnson, 1951;Kiddle et al. 1951;Pfander and Phillipson, 1953).…”

“…However, in the blood of the ruminai veins, the concentration of the VFA was in the order acetate > propionate > butyrate. Since Kiddle et al (1951) concluded that lymph was not an important pathway of VFA absorption, Masson and Phillipson (1951) proposed that butyrate and perhaps propionate were metabolized by the rumen epithelium. Kiddle et al (1951) came to the same conclusion from other, less strong evidence.…”

“…Since Kiddle et al (1951) concluded that lymph was not an important pathway of VFA absorption, Masson and Phillipson (1951) proposed that butyrate and perhaps propionate were metabolized by the rumen epithelium. Kiddle et al (1951) came to the same conclusion from other, less strong evidence. Support for this theory came from Pennington (1952) who showed In In vitro incubation studies that rumen epithelium could metabolize the VFA in the order butyrate > propionate > acetate.…”