Sampling Technique for Collection of Expired Co₂ in Studies Using Naturally Labelled ¹³c in Calves

Natural isotopic labelling of animal metabolic processes presents great advantages over the use of artificially enriched compounds. These advantages include the use of natural diets, low cost and easiness of handling, sampling and disposal. Changes in the 13 C/ 12 C ratio of expired CO 2 after ingestion of a test meal containing a variable proportion of C 3 and/or C 4 plant-derived products permits measurements of the immediate oxidation of dietary carbohydrates. A breathing device for collection of expired CO 2 and purification techniques are described. The breath-sampling device is composed of a polypropylene enclosure and a rubber bag. The rubber bag is blown up by the animal and a sample of the expired gas is transferred to a sampling glass holder in which a vacuum had been previously achieved. Sample purification of expired CO 2 is done by differential freezing.