The effect of lairage on Salmonella isolation from market swine

The objective of this paper was to evaluate the effect of lairage (holding > 12 h during transport to slaughter) in clean facilities on Salmonella iso lation from market swine. We tested 30 market-bound pigs (about 240 lb [110 kg]) on each of 10 occasions from an Iowa farrow-to-finish operation with about 600 sows. All pigs were slaughtered, and samples were collected at a large Midwest abattoir. On the farm, fecal samples were collected for cultu re of Salmonella. Pigs were alternately assigned to a lairage treatment (ho lding in a clean, disinfected facility at the National Animal Disease Cente r) group or a control group (remaining on the farm). After about 18 h, both groups were transported (about 137 km) to a large Midwest abattoir, commin gled, and slaughtered. After slaughter, samples were collected for culture of Salmonella (feces from the distal colon, ileocecal lymph nodes, cecal co ntents, ventral thoracic lymph nodes, subiliac lymph nodes, and carcass swa bs). Diaphragm sections were collected for serum ELISA. Salmonella enterica Derby was the only serotype isolated from farm fecal samples (3.4%. 10 of 290). Multiple serotypes (n = 17) were isolated from 71.8% (196 of 273) of the pigs when abattoir-collected samples were cultured: cecal contents (21. 2%. 58 of 273). distal colon contents (52%, 142 of 273), and ileocecal lymp h nodes (43.6%, 119 of 273). There were lower Samonella isolation rates fro m the lairaged pigs (P < 0.05). The predominant serotype isolated at the ab attoir varied by week of the study. This study suggests that pigs became in ternally contaminated with Salmonella after leaving the farm, possibly whil e in the abattoir holding pens. and that 18 h lairage, in clean facilities, does not increase shedding.