Use of antimicrobials in swine feeds in the United States
Catherine E. Dewey, DVM, PhD; Barbara D. Cox, MS; Barbara E. Straw, DVM, PhD; Eric J. Bush, DVM, MS; Scott Hurd, DVM, PhD
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Objective: To describe the use of in-feed antimicrobialsby stage of production in the United States swine industry.
Methods: National Swine Survey data from 712 farms werecollected by the National Animal Health Monitoring System (NAHMS)between 1989 and 1991. Specifically, producers were asked to recordover one 7-day interval the number of feeds they used, the phasesof production to which those feeds were fed, and which antimicrobialshad been added to the feeds. Producers were also asked whetherthe antimicrobials were used continuously or to treat a specificproblem.
Results: Of the 712 farms, 84 (12%) did not use anyantimicrobials in feeds. Across all participating farms, 39.5%of feeds contained no antimicrobial. Forty-one percent of thefeeds included one or more individual antimicrobials and 19% includedcombinations of antimicrobials. Creep, starter, and first-stagegrower pigs were more likely to be fed antimicrobials than second-stagegrowers, finishers, or adult swine (P=.02). Most (92.2%)antimicrobials were fed on a continuous basis. The age groupsmost likely to be fed antimicrobials to treat specific problemswere nursery, grower, and finisher pigs. The most commonly usedantimicrobials, listed in order of frequency were: tetracyclines,carbadox, bacitracin, tylosin, apramycin, and lincomycin. Carbadox,apramycin, and lincomycin were typically added to creep and starterfeeds. Bacitracin and tylosin were most often used in feeds forgrower and finisher pigs. Tetracyclines were fed to all ages ofpigs but were included more frequently in feeds for immature swinethan for mature swine.