Within-herd biosecurity and Salmonella seroprevalence in slaughter pigs: a simulation study

In Europe, on-farm biosecurity measures, involving a strict all-in/all-out batch-management system and decontamination of the rearing rooms between consecutive batches, are recommended to control Salmonella infection in growing pigs. However, implementation of these measures is often relaxed under common farming conditions. Therefore, this study was conducted to assess the relative contributions of batch-management system and room decontamination efficacy on Salmonella seroprevalence for different growing rates and subsequent slaughter ages of pigs. Because the impact of these factors cannot be easily evaluated by an observational approach in commercial farms, a stochastic simulation model representing the population dynamics, herd management, and Salmonella infection within a farrow-to-finish pig herd was used. Realistic levels were set for each factor under study (3 for batch-management system and slaughter age; 4 for room decontamination) to generate 54 simulation scenarios. Salmonella shedding prevalence in groups of slaughter pigs was then compared. A sensitivity analysis was performed to rank the impacts of the 3 factors on output. Batch-management system had little effect. In contrast, room decontamination efficacy had the greatest impact on Salmonella prevalence in pigs at slaughter. A drop in decontamination efficacy from 100 to 50%, with a strict all-in/all-out batch-management system and for all slaughter ages tested, noticeably increased (P<0.001) the prevalence and almost doubled it for the reference slaughter age. Our results suggest that the control of Salmonella in pig herds should primarily focus on room decontamination efficacy. Provided that a good level of room decontamination is ensured, some flexibility in batch management, in terms of pig mixing, would be acceptable to limit the number of underweight pigs delivered to the slaughterhouse.