Ruminal Metabolism of 3-Nitropropanoyl-D-Glucopyranoses from Crownvetch

Abstract

Compounds isolated from crownvetch (Coronilla varia L. β-nitropropionic acid (BNPA) and several glucose esters of BNPA, are reported to be toxic to nonruminant animals, but their lack of toxicity to ruminants has not been explained. Investigations of the metabolism of these compounds by in vitro rumen fluid incubations established that rumen microorganisms detoxify these aliphatic nitro-compounds. When incubated in rumen fluid, the esters, which are the naturally occurring form in crownvetch, were degraded to BNPA and presumably glucose within 4 hr, while BNPA was degraded to unknown products within 20 to 24 hours. Studies with a fistulated sheep suggested, but did not prove, a much faster rate of BNPA degradation in vivo (6 hr). BNPA was not degraded in rumen fluid that was centrifuged (microbe-free), establishing that the rumen microbiota are responsible for degradation. When diets containing lyophilized rumen fluid (incubated with BNPA) were fed to weanling meadow voles, no adverse effects were observed, establishing that detoxification of BNPA occurred during incubation. Further, sheep feeding trials with alfalfa and crownvetch (.6% BNPA by analysis) over a 4-week period resulted in equivalent weight gains. On the basis of these findings, we conclude that the aliphatic nitro-compounds in crownvetch are detoxified by rumen microorganisms in vivo; therefore this forage may be fed safely to ruminant animals.