The invention of this application provides a method of breeding poultry or a method of improving a feed conversion ratio (FCR), characterized by comprising feeding Bacillus coagulans at a late stage of poultry production in breeding of the poultry, and further provides a feed additive composition for use in improving poultry FCR comprising Bacillus coagulans strain CP3425 (International Accession Number NITE BP-01693) or a derivative or variant thereof.本申請案之發明提供一種特徵在於家禽類之飼養中包含於在家禽類之生產後期給予凝結芽孢桿菌(Bacillus coagulans)的家禽類之飼養方法或飼料轉換率(FCR)改善方法、以及包含凝結芽孢桿菌CP3425(國際寄存編號NITE BP-01693)或其衍生株或變異株之家禽類之FCR改善用飼料添加組合物。