Effects of the antimicrobial growth promoter tylosin on subclinical infection of pigs with Salmonella enterica serotype Typhimurium

Objective-To determine whether feeding tylosin, an antimicrobial growth pro moter, to pigs was associated with increased risk of infection with and exc retion of Salmonella enterica serotype Typhimurium. Animals-117 healthy pigs. Procedure-A commercial pelleted dry feed was given in 2 feeding trials. In trial A, 11 pigs were given feed with tylosin, ii pigs were given feed with out tylosin, and 11 pigs were given feed with tylosin before and feed witho ut tylosin after inoculation with S Typhimurium. In trial B, 44 pigs were g iven feed that contained tylosin, and 44 pigs were given feed without tylos in. Three weeks after the start of each trial, pigs were orally inoculated with approximately 5 x 10(6) colony-forming units of S Typhimurium. Feces w ere examined for S Typhimurium, using semiquantitative microbiologic techni ques before and for 5 or 6 weeks after inoculation. Serum antibody titers a gainst S enterica were measured by use of ELISA. Results-None of the pigs developed clinical signs of salmonellosis. However , after inoculation, S Typhimurium was isolated from feces of most pigs, an d all but 2 pigs developed serum antibodies against S enterica. Significant differences were not detected between experimental and control groups in e ither trial. Conclusions and Clinical Relevance-Results indicate that tylosin fed as an antimicrobial growth promoter to pigs may not be an important factor in pro moting infection with or excretion of S enterica serotype Typhimurium.