Estimation of the Salmonella enterica prevalence in finishing swine

Abstract

The study objective was to evaluate three methods of Salmonella enterica prevalence estimation in swine herds (faecal culture, culture of abattoir-collected samples, and serum ELISA). From each of six swine herds, we necropsied approximately 100 finishing pigs (>70 kg); one-half on farm and the other half at the abattoir, after transport and approximately 2·5 h holding. We collected the same samples for S. enterica culture at both locations (1 g faecal, 10 g caecal contents, ileocaecal lymph nodes, superficial inguinal lymph nodes, 25 g of gluteal muscle for serum ELISA). On farm, the 1 g faecal sample only detected 13·3% (2/15) of all positive pigs necropsied on farm. However, with abattoir and on-farm results combined, the faecal sample detected 57·4% (74/129) of positive pigs. Abattoir-collected samples provided prevalence estimates much higher than on-farm collected samples (39·9 vs. 5·3%; P<0·001). This study shows that faecal samples have a low sensitivity for detecting infected pigs and that abattoir-collected samples overestimate the on-farm S. enterica prevalence. For most herds, serology overestimated the on-farm culture prevalence.