This experiment was conducted to study the effects of ipriflavone on ruminal metabolism and concentration of 17β-estradiol and testosterone in rumen fluid in goat.This study consisted of two experiments,in vitro and in vivo.Ruminal fluid was incubated in anaerobic media in vitro with straw powder(0.6 g) and concentrates(0.3 g) as the substrate.Ipriflavone was added into the incubation with the final concentrations at 0,10,50,100 and 200 mg/L,respectively.In vivo,four local adult goats with permanent rumen fistulae were conducted into two periods by self-control design,control period and experiment period.In experiment period,ipriflavone was added into concentrates(1 mg/g concentrates) of diet.In exp.1,results showed that iptiflavone on 100 and 200 mg/L significantly enhanced ruminal metabolism.Levels of pH were reduced,the concentration of NH3-N and MCP were increased obviously.In exp.2,results showed that ipriflavone increased ruminal nitrogen metabolism in tendency,raised the concentration of acetate(A) and the percentage of acetate(P0.01),lowed the percentage of propionate(P)(P0.05) and the ratio of P∶A significantly(P0.01);Ipriflavone could significantly increase the concentration of 17β-estradiol and testosterone in ruminal fluid of goat(P0.05).These results may suggest that an interaction between ipriflavone and rumen microorganisms occurred.Ipriflavone could enhance nitrogen metabolism in rumen,affect carbohydrates metabolism,alter the fermentation pattern,and significantly increase the levels of 17β-estradiol and testosterone in ruminal fluid.