Comparison of plasma phyto-oestrogen levels in sheep and cattle after feeding on fresh clover

Abstract

Wethers and heifers were fed on freshly cut pasture (red clover, Mt. Barker or Tallarook subterranean clover, or ryegrass) and the blood plasma concentration of the phyto-oestrogens and their metabolites estimated 5 hr, 24 hr, and 6 days after the beginning of the feeding. The heifers were allowed to graze the pastures after the first day. On the basis of increase in teat length in the wethers, red clover and Tallarook were estimated to have equivalent oestrogenicity ; Mt. Barker was much less active. Qualitatively, the metabolism of formononetin and biochanin A appeared similar in the two species, but there was evidence that the rates of metabolism and of conjugation were faster in cattle than in sheep. The findings are discussed in relation to an infertility syndrome in dairy cattle.