Response of Finishing Pigs with Different Rates of Prior Performance to Antimicrobials Fed at Growth Promoting or Therapeutic Levels

Previous work conducted at· this station has involved sorting pigs according to prior performance during the grower period into uniform groups for the finishing period. Results of these studies suggest that pigs having slow previous growth rates continued to grow more slowly than pigs with fast or intermediate prior growth rates. Further, the use of growth promoting levels of antimicrobials appeared to stimulate the performance of pigs having fast and intermediate growth rates without a similar improvement in the performance of slow growing pigs. Therapeutic levels of antimicrobials were observed to improve average daily gains in a study utilizing slow growing pigs. Thus, the present study was conducted to determine if the response to antimicrobials is affected by previous performance and if growth-promoting and therapeutic levels of antimicrobials elicit different responses in finishing pigs