Effect of daidzein on in vitro fermentation by microorganisms from the goat rumen

Isoflavones are a group of phytoestrogens found in many plants, and daidzein is one of their major metabolites. Previous studies have shown that daidzein affects growth of rumen bacteria and intestinal microflora. This study investigated effects of daidzein on rumen microbial fermentation. Substrate containing ground Chinese wildrye hay (7 g/L), corn grain powder (2.1 g/L) and soybean meal (0.9 g/L) was fermented in vitro by mixed rumen microorganisms and substrate containing rice straw (8 g/L) by rumen anaerobic fungi from four rumen fistulated male goats. Results with mixed rumen microorganisms showed that daidzein treatment had no effect on the total VFA, but maximized propionate at about 10 mg/L (quadratic P<0.01). As a result, the ratio of acetate to propionate was minimized at 10 mg/L (quadratic P<0.05). Daidzein treatment also minimized NH3-N at 10 mg/L (quadratic P<0.01), but had no effect on microbial crude protein. The fermentation time-course study showed that the effect of daidzein at 10 mg/L on production of acetate and propionate became significant after 1 h of fermentation, while the effect on NH3-N content became evident after 5 h. In a culture of the rumen anaerobic fungus Neocallimastix sp., daidzein maximized cumulative gas production and specific growth rate to half of the gas pool at 10–50 mg/L, but had no effect on dry matter loss. Results indicate potential regulating effects of daidzein on rumen microorganisms that could be useful in the rumen function.