Metabolism of pyrrolizidine alkaloids in the ovine rumen. IV. Effects of chloral hydrate and halogenated methanes on rumen methanogenesis and alkaloid metabolism in fistulated sheep

Abstract

Five halogenated methane analogues (bromoform, chloroform, iodoform, carbon tetrabromide, and carbon tetrachloride) have been shown to inhibit methane formation in the sheep's rumen as well as in rumen fluid in vitvo. On a molar basis the methane analogues were 100-200 times as effective as chloral hydrate in vitro, but in the rumen this difference was reduced by a factor of 10 with four of the compounds and to parity with chloral hydrate in the case of carbon tetrachloride. When rumen methanogenesis was inhibited by administration of chloral hydrate, bromoform, or iodoform, the time taken for metabolism of 2 g of Heliotropium europaeum alkaloids was reduced to 25-40% of that taken in animals not so treated. These results support the conclusion that inhibition of methanogenesis may be a useful protective measure for sheep ingesting plants which contain hepatotoxic pyrrolizidine alkaloids.