Investigation of the Distribution of Salmonella within an Integrated Pig Breeding and Production Organisation in the United Kingdom

To examine patterns of Salmonella herd infections in units linked by common sources of pigs, the study examined pooled pen faeces samples from 161 nursery and finishing units in a UK integrated pig enterprise. An epidemiological questionnaire was also completed by investigators for each farm. Salmonella was isolated from 630 (19.5%) of the samples: S. Typhimurium was found in 387 (12%) and S. Derby in 157 (4.9%) samples; 111 units yielded at least one sample containing Salmonella. The proportion of Salmonella-positive samples from positive farms ranged from 5% to 95%. In a univariable risk factor analysis, increasing length of time as a pig farm was positively associated with the detection of Salmonella in a herd. Larger farms (>500 pigs) were significantly more likely to be positive for S. Typhimurium than smaller farms. There was an association between Salmonella serovars isolated in the present study and those subsequently isolated in breeding herds linked to the integration. 1. Introduction Recent European attribution studies have implicated pork as a principal source of human salmonellosis [1, 2], and minimising the carriage of Salmonella by slaughter-age pigs is considered to be a useful control for Salmonella contamination on carcasses [3–5]. The large herds of modern pig production [6], plus movements of pigs between premises at different life stages, offer opportunities for the maintenance and dissemination of Salmonella infections that may originate in breeding stock or be acquired from endemic environmental contamination of premises [7, 8]. On-farm risk factor analyses have commonly identified associations between herd Salmonella status or individual infections and feed type, hygiene, biosecurity, contact between pig groups, number of suppliers, previous clinical salmonellosis, and certain intercurrent diseases [9]. Vertically integrated pig companies control sequential production levels, from genetic or multiplier breeding herds to slaughter of finished pigs. They may use external contractors to implement commercial breeding and finishing [10], moving pigs between contractors’ sites between life stages. Such integrated pig production systems may potentially offer more control over sources of Salmonella infection, but the risks of dissemination of infection that is present in the upper tiers of the production pyramid may also be substantial. The present report describes a study examining Salmonella contamination on multiple sites that were part of a single integration sharing a common breeding source. Pooled faeces sampling coupled with