Detection of high serological prevalence and comparison of different tests for Salmonella in pigs in Northern Ireland

Thirty-one farrow-to-finish pig units with a Zoonoses National Control Programme (ZNCP) for Salmonella above the UK target of 10 per cent during the previous 12 months were selected for the study. Pooled faecal samples were collected from different groups of pigs. Furthermore, mice, rat and bird faeces and carcases were collected, if found on the unit. In total, 937 samples were collected on-farm and analysed for Salmonella. The four carcases selected monthly per producer by the slaughterhouse for the British Pig Executive ZNCP Salmonella Programme were tested for antibodies to groups B and C with a mix-ELISA test. The same four carcases were swabbed externally and internally, mesenteric lymph nodes (MLNs) were collected and colonic contents were swabbed. A wide variety of Salmonella serovars was isolated from the samples. Most of the isolates were detected in the rearing herd (on-farm) and in the MLNs (slaughterhouse). There was no correlation between ELISA results from the meat juice and bacteriological isolations using Spearman correlation analyses. Furthermore, no significant association was found between positive results of ELISA and positive results from the bacteriological samples taken.