Title:

Influence of defoliation frequency and severity on phytoestrogen concentrations in red clover and white clover

Perennial forage legumes are an important feed source for dairy, contributing to food and protein security by boosting milk yield and quality. Some forage legumes synthesize and accumulate phytoestrogen in their tissue while mimicking the mammalian sex hormone estrogen. Excessive intake of high estrogenic forage legumes may disturb the reproductive health of animals and transfer them to milk. These compounds in plants are recognized for their defensive functions under various stress conditions. We conducted a field experiment to evaluate how two management practices, defoliation frequencies (3 vs. 5 times/growing season) and defoliation severity (5 cm vs. 10 cm residual height), influence phytoestrogen accumulation in red clover (Trifolium pratense L.) and white clover (T. repens L.). Our result showed that the average total phytoestrogen level was 140 times higher in red clover than in white clover. Red clover defoliated five times in a growing season produced 34.5% more average total phytoestrogen than when defoliated three times; however, white clover did not exhibit this difference. Defoliation severity did not influence the phytoestrogen level in either red clover or white clover. In both red clover and white clover, formononetin and biochanin A are major phytoestrogens; cumulatively, they occupy 85% and 65% of total phytoestrogens, respectively. Our findings highlight that average phytoestrogen levels in more frequently defoliated red clovers are higher than those harvested less frequently in a growing season. White clover is a potential source of perennial forage legumes with low estrogen levels.

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