The object of the invention is to enable production of high quality eggs inpoultry and to provide a method for improving productivity thereof. Theinventionprovides a method for producing a hen egg having improved quality andproductivity,the method characterized in comprising a step for feeding a hen onsupplemented feedobtained by adding to poultry feed an immunostimulating substance produced bycytolysis that accompanies sporulation of MRE symbiotic bacteria and/or onsupplemented drinking water obtained by adding the immunostimulating substancetodrinking water, wherein the immunostimulating substance is obtained byculturing theMRE symbiotic bacteria, leaving the resulting culture fluid in a depletedstate to therebycause the symbiotic bacteria to convert to endospores, and removing impuritiesincluding the endosporic symbiotic bacteria from the culture fluid.
