The rates of production of volatile fatty acids in the rumen. III. Measurement of production in vivo by two isotope dilution procedures

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Abstract
(1) Production of volatile acid in the rumen of sheep fed at 12-hourly intervals on a mixture of wheaten hay and lucerne hay has been measured by two isotope dilution procedures involving continuous infusion of 14C-labelled fatty acid into the rumen and determination of the concentration of 14°C in the rumen acid throughout the feeding cycle. In the first procedure the varying rate of production was matched by a varying rate of infusion so that a constant concentration of label was maintained in the rumen acid. In the second procedure a constant rate of infusion was maintained and a mean value obtained for the concentration of label in the rumen acid during the cycle. Production values calculated from the data from both procedures were similar: approximately 5 moles of volatile acid were produced per kilogram of dry fodder. (2) This same rate of production was found for rations of 360, 450, and 675 g dry fodder fed at 12-hourly intervals.