Different feed withdrawal times before slaughter influence caecal fermentation and faecal Salmonella shedding in pigs

The effects of different pre-slaughter feed withdrawal times (FWT) on the gastrointestinal tract (GIT) weight and the gut environment of pigs and Salmonella shedding were investigated. Trial 1 evaluated the effects under experimental conditions (feed withdrawal for 18, 30 and 36 h) and trial 2 under commercial conditions (15 and 30 h). In trial 1, the GIT weight tended to decrease (P = 0.07), the caecal pH increased (P < 0.0001), short-chain fatty acids (SCFA) decreased (P < 0.001) and percentage of branched-chain fatty acids (BCFA) increased as FWT increased. Similar results were observed in trial 2, but Enterobacteriaceae numbers and Salmonella positive pigs tended to increase whereas lactobacilli decreased (P < 0.0005) as FWT increased. The increase in FWT involved changes in the gut microbial ecosystem that could be associated with the trend of increased caecal Enterobacteriaceae and Salmonella in faeces, and may represent a higher risk of carcass contamination in cases of laceration of viscera.