Adaptation by sheep to isoflavones in clover

Abstract

Vaginal mucus scores and uterine weights of ovariectomized ewes that grazed subterranean clover for 13 days prior to tests were similar to those from ewes fed non-oestrogenic rations during this pre-treatment, if the leaves of test clovers contained high concentrations of formononetin (F) (Yarloop and Dinninup). No responses were obtained from subterranean clovers low in F, but high in genistein (G) or biochanin A (BA) (Clare and Bacchus Marsh) except for a group which was fed a non-oestrogenic diet during pre-treatment, and which gave a positive mucus test, but not a stgnificant uterine weight response. These results indicate that ewes can become non-responsive to G and BA, but not to F, and offer an explanation for some inconsistencies among bioassays of subterranean clovers. The task of selection and breeding of subterranean clover seems to be simplified since G and BA are unlikely to be harmful.