An immunogenic composition comprising a leukocidin M / F antigen and capable of imparting toxin neutralizing activity to a ruminant which is an animal to be administered. The immunogenic composition makes it possible to prevent or alleviate symptoms of the disease caused by Staphylococcus aureus in ruminants. The leucocidin M / F antigen is a protein or peptide having at least a part of the amino acid sequence constituting the leukocidin M protein, or a protein or peptide having at least a part of the amino acid sequence constituting the leukocidin F protein. The immunogenic composition may further contain bacterial cell antigens of Staphylococcus aureus.
