ARS | Publication request: Bacteriological and Serological Salmonella Prevalence in Finishing Pigs

Submitted to: Pig Veterinary Society International Congress Proceedings
Publication Type: Proceedings/Symposium
Publication Acceptance Date: April 22, 2004
Publication Date: July 1, 2004
Citation: Rostagno, M.H., Hurd, H.S., McKean, J.D. 2004. Bacteriological and serological Salmonella prevalence in finishing pigs [abstract]. Proceedings of the International Pig Veterinary Society. p. 649.

Technical Abstract: This study consisted of an on-farm survey to determine the Salmonella enterica infection prevalence in finishing pigs from multiple production sites. The aim was to evaluate the stability of Salmonella prevalence (bacteriological and serological) in finishing pig groups produced by each system. Six finishing production sites were visited 6 times each. At each visit, 30 individual fecal samples were collected directly from the rectum. At slaughter, 50 individual meat samples (diaphragm) were collected per load. Fecal samples were selectively enriched and analyzed for the presence of Salmonella enterica. Meat samples were frozen and thawed. The resulting liquid ('meat juice') was collected and analyzed for the presence of antibodies against Salmonella. All finishing production sites were Salmonella-positive in at least 2 fecal (bacteriological) and 4 meat (serological) samplings. The overall bacteriological prevalence of Salmonella-positive pigs was 12.9% (95% C.I. 8.0 ' 17.8%), whereas the serological prevalence found was 35.4% (95% C.I. 24.5 ' 46.4%). Although the overall prevalence estimated by fecal and meat samplings differed (p < 0.05), a Pearson's correlation coefficient (r) of 0.64 (p < 0.01) was found. However, the striking result found in this study consisted in a wide variation in the Salmonella prevalence (bacteriological and serological) of different finishing pig groups within individual production sites. The wide variation found did not allow the categorization of the sites (statistically) as high or low prevalence systems. Possible reasons for the wide variation found within production sites are: 1) occurrence of intermittent shedding and clusters, and 2) evolution and resolution of Salmonella infection epidemics. This study demonstrates that both, bacteriological and serological estimates of Salmonella enterica prevalence in swine production systems are not consistent among cohorts over time, and also, that Salmonella infections in swine populations are very dynamic requiring further investigation. As a direct consequence of the results obtained in this study, a critical question remains: Are there high and low Salmonella prevalence farms, or is it just a matter of timing?