AimsThe objective was to determine the effect of biochanin A (BCA), an isoflavone produced by red clover (Trifolium pratense L.), on corn fermentation by rumen micro-organisms. Methods and ResultsWhen bovine rumen bacterial cell suspensions (n=3) were incubated (24h, 39 degrees C) with ground corn, amylolytic bacteria including group D Gram-positive cocci (GPC; Streptococcus bovis; enterococci) proliferated, cellulolytic bacteria were inhibited, lactate accumulated and pH declined. Addition of BCA (30gml(-1)) inhibited lactate production, and pH decline. BCA had no effect on total amylolytics, but increased lactobacilli and decreased GPC. The initial rate and total starch disappearance was decreased by BCA addition. BCA with added Strep. bovis HC5 supernatant (containing bacteriocins) inhibited the amylolytic bacteria tested (Strep. bovis JB1; Strep. bovis HC5; Lactobacillus reuteri, Selenemonas ruminatium) to a greater extent than either addition alone. BCA increased cellulolytics and dry matter digestibility of hay with corn starch. ConclusionsThese results indicate that BCA mitigates changes associated with corn fermentation by bovine rumen bacteria exvivo. Significance and Impact of the StudyBCA could serve as an effective mitigation strategy for rumen acidosis. Future research is needed to evaluate the effect of BCA on mitigating rumen acidosis invivo.