The adequacy of sample type/weight and incubation period on detection of Salmonella spp. in slaughter cattle

Ecole Nationale Veterinaire de Lyon, France.

The purpose of this study was to examine the adequacy of different sample types (fecal and rumen content), rumen-content sample weight (1, 10, and 25 g), and incubation period on the detection of Salmonella spp. in grass-fed beef cattle at slaughter. The culture technique was the same for all samples and followed the Australian Standard (AS 1766.2.5-1991). Sample adequacy was defined as the ratio between the overall prevalence, as obtained from samples identified as positive by any sample type/weight, and the estimated prevalence, as obtained from samples identified as positive by a particular sample type/weight. Sample adequacy reflects the likelihood of a sample of a particular type and weight to contain the organism of interest and hence is related to the sensitivity of the diagnostic test. It was found that sample adequacy differed between sample types and weights: 37.5% for both a 10-g fecal sample and a 1-g rumen sample, 77.1% for a 10-g rumen sample, and 79.2% for a 25-g rumen sample. On this basis, it is strongly recommended that sample type and weight be considered in the design of studies that aim to quantify Salmonella contamination in cattle.