Fresh and ensiled forages as a source of estrogenic equol in bovine milk: a review

Isoflavan equol has recently been assessed in human nutrition as a potent estrogen with various health benefits. It is produced by intestinal microflora from isoflavones (IF) formononetin and daidzein. These dietary precursors are present particularly in soy products. However, only 20-35% of the Western adult population is capable of producing equol from the ingested IF. Cow's milk was proved to be an important source of equol produced from the IF in the rumen and intestines. Among forages, red clover (Trifolium pratense) is by far the most important source of both the IF. Their contents in fresh red clover forage are affected by variety and by several environmental factors. Leaves have the highest IF contents. Available data on changes in IF contents during wilting, drying, and ensiling are ambiguous. Content of equol in milk produced by dairy cows fed fresh or ensiled red clover can be at the level of several hundreds mu g per litre.