Use of antimicrobials in swine feeds in the United States

Abstract

Objective: To describe the use of in-feed antimicrobials by stage of production in the United States swine industry. Methods: National Swine Survey data from 712 farms were collected by the National Animal Health Monitoring System (NAHMS) between 1989 and 1991. Specifically, producers were asked to record over one 7-day interval the number of feeds they used, the phases of production to which those feeds were fed, and which antimicrobials had been added to the feeds. Producers were also asked whether the antimicrobials were used continuously or to treat a specific problem. Results: Of the 712 farms, 84 (12%) did not use any antimicrobials in feeds. Across all participating farms, 39.5% of feeds contained no antimicrobial. Forty-one percent of the feeds included one or more individual antimicrobials and 19% included combinations of antimicrobials. Creep, starter, and first-stage grower pigs were more likely to be fed antimicrobials than second-stage growers, finishers, or adult swine (P=.02). Most (92.2%) antimicrobials were fed on a continuous basis. The age groups most likely to be fed antimicrobials to treat specific problems were nursery, grower, and finisher pigs. The most commonly used antimicrobials, listed in order of frequency were: tetracyclines, carbadox, bacitracin, tylosin, apramycin, and lincomycin. Carbadox, apramycin, and lincomycin were typically added to creep and starter feeds. Bacitracin and tylosin were most often used in feeds for grower and finisher pigs. Tetracyclines were fed to all ages of pigs but were included more frequently in feeds for immature swine than for mature swine.