Techniques to Determine Rate of Metabolism of C14-Labeled Alfalfa in the Bovine Rumen

Abstract

In an earlier experiment, it was not possible to predict with certainty the rate of metabolism of one feeding of C14-labeled alfalfa hay, because rumen volatile fatty acids (VFA) arising from the metabolism of unlabeled hay from previous or subsequent feedings diluted specific activity (SA) of VFA arising from the single feeding of labeled hay. In this study the extent of dilution of SA of rumen VFA by VFA arising from previous or subsequent feedings was determined by fasting a cow after a single feeding of C14-labeled alfalfa or by emptying her rumen of all digesta, replenishing the rumen with strained rumen fluid before feeding C14-labeled alfalfa, then fasting the cow. In both instances, SA of rumen VFA increased rapidly after feeding, reached a peak between 5 and 9 hr, then declined. The decline was less rapid than in the earlier experiment when the animals were fed hay at 12-hr intervals.On the basis of total activity of rumen VFA, the most active rumen metabolism of C14-labeled alfalfa occurred between 4 and 8 hr. The most active metabolism of cellulose occurred during the first 12 hr, with little after 36 hr.