Vet. Res. 38 (2007) 835-848
DOI: 10.1051/vetres:2007034

Risk factors for Salmonella seroconversion of fattening pigs in farrow-to-finish herds

Pierre-Alexandre Beloeil^{a, b}, Claire Chauvin^a, Karine Proux^a, Christelle Fablet^a, François Madec^a and Ahmadou Alioum<sup>c

a</sup>  Afssa, French Agency for Food Safety, Pig and Poultry Veterinary Research Laboratory, Epidemiology and Quality Assurance in Pig Production Research Unit, Zoopôle, BP 53, 22440 Ploufragan, France
^b  Present address: European Food Safety Authority (EFSA), Zoonoses Unit, Largo N. Palli 5/A, 43100 Parma, Italy
^c  INSERM, E 03-38 & ISPED - Université Victor Segalen Bordeaux 2, 33076 Bordeaux Cedex, France

(Received 20 September 2006; accepted 11 May 2007 ; published online 20 September 2007)

Abstract - We did a prospective observational 9-month long study to quantify risk factors of managerial and hygiene practices, and pig-health status for Salmonella seroconversion of fattening pigs reared in subclinically infected French farrow-to-finish farms. During the fattening phase, 2 649 pigs belonging to the same batch of contemporary pigs, from 89 conventional farrow-to-finish farms were individually followed and regularly blood sampled on a monthly basis. Farm recruitment was based on the farmer's willingness to cooperate. Pig status was assessed using an indirect ELISA test. Evolution of the serological status was studied by means of survival analysis. A Cox proportional-hazards model, taking into account the clustering of animals at the farm level, was used to examine the effects of explanatory variables on the time to Salmonella seroconversion of pigs. Applying group level antibiotic treatment to the pigs during the fattening period (Hazard Ratio (HR) = 2.4; 95% CI: 1.7, 3.4) was identified as a risk factor for Salmonella seroconversion, as the presence of residual Salmonella contamination in the fattening pen before placing the pigs into the pens (HR = 1.9; 95% CI: 1.2, 2.9). Porcine reproductive and respiratory syndrome virus (PRRSV) seropositivity during the fattening period also indicated an increased hazard for seroconversion (HR = 1.6; 95% CI: 1.1, 2.5). The batch size was identified as a risk factor for Salmonella seroconversion: the higher the number of pigs was in the fattening room followed, the higher was the risk (HR = 1.05 for a 10-pig increment; 95% CI: 1.03, 1.06). The biosecurity measures of wearing specific clothes before entering the facilities (HR = 0.5; 95% CI: 0.3, 0.9) and enclosing the pig farm facilities were protective (HR = 0.4; 95% CI: 0.2, 0.8).

Key words: Salmonella / pigs / seroconversion / risk factors / survival analysis

Corresponding author: pierre-alexandre.beloeil@efsa.europa.eu

© INRA, EDP Sciences 2007