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Availability and Metabolism of Various Substrates, in Ruminants. II. Rate of Acetate Oxidation as Affected by Availability of Substrate¹

Department of Dairy Science, University of Illinois, Urbana

ABSTRACT

The sodium and potassium salts of acetic acid were infused into the external jugular vein of a 455-kg. Holstein steer at a rate to supply 20.27, 45.00, and 65.00 g. of free acetic acid per hour for a period of 7 hr. Acetate-1-C¹⁴ of high specific activity and of the same salt form was mixed thoroughly with the carrier (unlabeled) acetate before being infused.

The expired gases were measured, sampled, and analyzed for CO₂ content and their radioactivity determined. From the specific activity of the expired CO₂ and the total carbon dioxide output, the grams of infused acetate oxidized, as well as the rate of oxidation, was determined. Of the 142, 315, and 455 g. of acetate administered during the low, medium, and high rates of infusion, 103, 188, and 333 g., respectively, were oxidized to CO₂ and expired. The mean rates of acetate oxidation were calculated to be 15.46, 28.12, and 51.38 g/hr for the three rates of infusion, respectively. At the highest rate of oxidation (51.38 g/hr) acetate accounted for 34.2% of the total carbon in the expired CO₂. The contribution of the oxidized acetate toward the maintenance energy requirement of the animal was estimated to be 37.4%.

The technique used for the collection, measurement, and sampling of the expired gases is applicable to the study of factors affecting the oxidation of various metabolites to carbon dioxide. The simplicity of operation of the mechanical equipment and the normalcy of the animal under the experimental conditions make the technique extremely advantageous for studies of this type. The large size of the expired gas aliquot and the high counting efficiency of the C¹⁴O₂ permit the use of low levels of radioactivity, thereby reducing hazard from radiation exposure.

¹ Supported in part by a grant from the Rockefeller Foundation.

² The data presented are from a thesis submitted by the senior author to the Graduate College, University of Illinois, in partial fulfillment of the requirements for the degree of Doctor of Philosophy.