Reference | Wagner2008 (10130)

The five treatment protocols, which consisted of the two antimicrobials chlortetracycline (CTC) and tylosin, each administered by two methods, pulse and low-level continuous, along with any antimicrobial-free control were randomly assigned to 21 swine barns. Each of the five treatments was randomly assigned to four barns with the exception of the pulse-tylosin treatment, which was assigned to five barns to equalize the number of pens in each treatment. In most barns, three or four pen clusters were further randomly selected for testing but four barns had six pen clusters selected. A pen cluster was three adjacent pens holding a total of 60 pigs (20 per pen), and at every collection six or seven samples were collected out of each pen in the cluster for a total of 20 samples/cluster or about one-third of the pigs. Each treatment was assigned to a total of 16 pen clusters, with the exception of the antimicrobial-free treatment, which had only 15 pen clusters.CTC was fed at 100 g/ton of feed continuously throughout the finishing period until 2 weeks prior to marketing. Continuous tylosin was fed at 40 g/ton for the entire time the pigs were in the barn (17 weeks). Pulse doses of CTC and tylosin, 400 and 100 g/ton, respectively, were fed for 1 week, followed by 3 weeks of no antimicrobial, another week of antimicrobial, and finally concluding with no antimicrobials for the 12 weeks the pigs remained in the barns.

Feeder pigs from a single source were conveniently assigned to pens. One day after arrival for the beginning of the feeding period (period 1), six or seven fecal samples were collected from each pen of a cluster. If possible, when the pigs were observed defecating, fecal samples were obtained prior to it hitting the ground. Otherwise, a portion of the manure was obtained from piles that had presumably just dropped onto the pen floor. Care was taken to avoid touching the floor when collecting the sample. The treatment protocols were initiated at the same time these initial fecal samples were collected. A second set of fecal samples was collected in a similar manner when the pigs were near market weight, approximately 9 weeks after placement (period 2).

AST Method: None

Reference explicitly reports AST breakpoints: False

Reference reports using a MIC table: True