Abattoir based survey of Salmonella in finishing pigs in the United Kingdom 2006-2007.

ABSTRACT

All European Union (EU) Member States (MSs) were required to conduct a baseline survey from October 2006 to September 2007 to estimate the prevalence of Salmonella infection in finisher pigs at slaughter. In the United Kingdom (UK), samples for microbiological culture were collected from the ileo-caecal lymph nodes, from carcass swabs and from caecal contents. Meat juice samples were also collected for testing in an enzyme-linked immunosorbent assay (MJE) to detect a serological response. Salmonella was isolated from 22% (CI95% 19-25%) of ileo-caecal lymph nodes, 15% (CI95% 12-18%) of carcass swabs and 22% (CI95% 19-26%) of caecal contents. A quarter (25%, CI95% 22-29%) of MJE samples were positive for Salmonella antibodies (cut-off, S/P≥0.25). The most frequently identified serovars were Salmonella typhimurium (57%) and Salmonella derby (26%). The results were used to investigate some factors associated with Salmonella infection in slaughter pigs. The weight of the carcass was significant, with a lower probability of obtaining a positive meat juice result from pigs with a weight greater than 75 kg (p=0.03). The weight of the lymph node sample was significantly associated with Salmonella status, with a heavier sample of lymph nodes being more likely to be positive (OR=2.16 CI95% 1.07-4.39). 'Carcass weight' in two of the classes - 75-79 kg and 80-84 kg - (OR=0.44 CI95% 0.28-0.70; OR=0.64 CI95% 0.49-0.85) and 'fewer-than-1500-pigs' scheduled for slaughter on the day of sampling' (OR=0.41 CI95% 0.24-0.71) were also associated with a reduced risk of isolating Salmonella from lymph node. The model for carcass swabs showed a positive association with 'time-elapsed-since-the-start-of-the-line' indicating a higher risk of contamination as the day progressed (p<0.01). This model also showed positive association between isolation of Salmonella from a carcass swab and the occurrence of Salmonella in caecal contents from the same pig (OR=2.22 CI95% 1.38-3.59) and a negative association with time in singeing units (OR=0.88 CI95% 0.79-0.98).