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Absorption of Organic Acids from the Omasum^1,2,

Department of Dairy Science, Pennsylvania State University, University Park

ABSTRACT

Absorption of volatile fatty acids (VFA) and lactic acid from the omasum of 4- or 5- mo.-old Holstein calves was studied by two methods. The first consisted of a study of the relative concentrations of these acids in the contents of the stomach compartments of six calves in relation to concentrations of chromic oxide remaining from previous oral adininistration. On a dry matter basis, levels of chromic oxide increased in order from the rumen, to the reticulum, to the omasum, to the abomasum; and, in the same order, VFA declined. The ratios of VFA to chromic oxide indicated a decrease in VFA of 51% from the reticulum to the omasum and a further decrease of 83% from the omasum to the abomasum.

The second method involved injection of sodium-n-butyrate-1-C¹⁴ into the exteriorized omasum of two calves. Organic acid levels and distribution of C¹⁴ activity were determined on samples of blood drawn simultaneously from the omasal vein and the carotid artery at various time intervals during 1 hr. following injection. The animals then were sacrificed and concentrations of acids and distribution of label in the ingesta of the stomaeh compartments were studied. Butyrate-C¹⁴ was absorbed rapidly from the omasum into the blood of the omasal vein, peak concentrations appearing at 5 to 10 min. after injection. Labeled metabolite continued to be absorbed throughout the experiment. Conversion of butyrate to other VFA occurred in the omasum, as indicated by the presence of label in the acids isolated from ingesta in that organ. The appearance of 50% of the recovered label in omasal blood in the form of lactic acid suggests an unknown pathway for the conversion of butyrate to lactate by omasal epithelium. Average concentrations of butyric, propionic, and acetic acids were greater in the omasal vein blood than in the carotid artery blood; the reverse was true for lactic acid. It is concluded that absorption of organic acids does occur from the omasum and apparently in considerable magnitude.

¹ Authorized for publication on October 6, 1960, as Paper No. 2494 in the Journal Series of the Pennsylvania Agricultural Experiment Station.

² Taken in part from a thesis presented by the senior author in partial fulfillment of requirements for the M.S. degree.

³ Present address: U. S. Air Force.