Drag swab efficiency factors when sampling chicken manure

This study examines drag swabbing distance, media for moistening the drag swabs, and site selection when sampling a laying facility by drag swabbing manure piles. Manure piles at a laying facility in California's San Joaquin Valley were sampled with drag swabs over various distances. Samples were cultured for Salmonella spp. with standard laboratory methods, and most probable number calculations. Salmonella spp. counts were expected to be highly variable because of reported clustering. Therefore, total bacteria and Escherichia coli, which were assumed to have a more uniform distribution on the surface of the manure, were additionally used as proxies for Salmonella. Media for moistening the swabs were compared by seeding postswabbing samples with Salmonella typhimurium, and culturing at different delay times. Total bacterial counts were compared between samples that were obtained from either wet or dry surfaces. Numbers of Salmonella spp. and total bacteria peaked within 120 feet of swabbing distance. Higher total bacteria counts were obtained by swabbing wet areas rather than dry areas, but the distance that could be swabbed effectively was shorter in wet areas. Moistening media selected for the swab resulted in statistically different culture counts, but did not show any important difference in maintaining Salmonella viability over a 48-hr period when the samples were kept at refrigerated temperatures. Once swabs became fully loaded with fecal material, bacterial numbers failed to increase with further use. Overuse of a swab may result in failure to detect Salmonella enteritidis on chicken manure if the distribution of this organism is clustered.