Metabolism of pyrrolizidine alkaloids in the ovine rumen. III. The competitive relationship between Heliotrine metabolism and methanogenesis in the rumen fluid in vitro

Abstract

Inclusion of up to 80% hydrogen in the gas phase markedly stimulated the in vitro metabolism of heliotrine in sheep rumen fluid. The maximal rate of heliotrine breakdown under these conditions was twice that obtained when cyanocobalamin was added and 10 times the rate in unsupplemented rumen fluid. A maximal rate of heliotrine metabolism equal to that in the presence of 80% hydrogen gas could be obtained with a pure carbon dioxide atmosphere if certain inhibitors of methanogenic bacteria were added to the rumen fluid. It is concluded that the heliotrine-metabolizing bacteria are normally at a disadvantage in competition with the methanogenic bacteria for metabolic hydrogen, and that inhibition of the latter organisms in vivo could provide a basis for development of effective prophylaxis in sheep at risk with Heliotropium europaeum in the field.