The invention relates to a method for testing a fodder component for the feeding of ruminants via ruminal fermentation simulation known in itself in an artificial rumen so that the fodder component is decomposed by the action of microbes into fermentation products utilizable in the animal's metabolism and providing the nutritive substances needed by the animal. In the method, fermentation products substantially proportional to the yield of the animal are measured and compared with corresponding results achieved using known fodder components whose productional effect is known. Based on the comparison, the effect of the fodder component on the animal's yield is determined.