Metabolism of Oestrogenic Isoflavones in Sheep

Abstract

BIOCHANIN A (I), genistein (II) and formononetin (III) have been shown to act as oestrogens in mice, rats and guinea-pigs, and are considered to be responsible for the depression of fertility noted in sheep grazing subterranean clover¹. An examination has now been made of the urinary metabolites produced when these isoflavones are administered to sheep. Nilsson² reported that biochanin A, injected intraperitoneally into rats, was largely excreted in the faeces as biochanin A and genistein or their conjugates. In our experiments with sheep, only trace amounts of free or conjugated isoflavones were found in the faeces.