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The goal of this study was to determine the prevalence of Listeria monocytogenesin sows slaughtered at a single Midwestern plant on two occasions (trial 1, n= 179 sows; trial 2, n= 160 sows). Fecal samples collected antemortem (trial 1) as well as animal tissues, and carcass swabs collected at the abattoir (trials 1 and 2) were analyzed. Eight isolates of L. monocytogeneswere recovered from five samples that represented 0.18% of the total samples (n= 2,775). In trial 1, L. monocytogeneswas detected in a tonsil sample (0.6%; 1 positive of 181 tonsils), in a carcass (0.6%; 1 positive of 179 carcasses), which was sampled prior to the organic rinse, and in two chopped meat block samples (1.2%; 2 positive of 165 samples). In trial 2, L. monocytogeneswas only detected in a single chopped meat block sample (0.15%; 1 positive of 688 total samples). These data indicate the low prevalence of L. monocytogenesin the cull sow.

Recent research has shown that much preharvest Salmonella entericainfection in pigs occurs immediately before slaughter during this rest period in the contaminated abattoir holding pens. The objective of this study was to evaluate a potential intervention strategy to reduce the prevalence of S. enterica–positive pigs at slaughter, which consisted of resting pigs prior to slaughter on their transport vehicle, instead of in the abattoir holding pen. Additionally, the effect of transportation of pigs from farm to the abattoir on S. entericaprevalence was investigated. A total of 120 animals were included in the experiment, divided in four replicates (n= 30 pigs per replicate). Fecal samples were collected from each animal at the farm and at the abattoir, where 15 randomly chosen pigs were unloaded and moved to a holding pen, while the remaining 15 pigs stayed in the transport trailer. After approximately 1.5 h of resting, both groups were slaughtered. Samples collected included distal ileum portion, cecal contents, and ileocecal lymph node. The overall S. entericaprevalence (pigs positive in at least one of the samples collected at slaughter) was higher for pigs held in the abattoir pens (40.7% versus 13.3%, P< 0.05). There was no difference (P> 0.05) for the S. entericaprevalence before and after transportation from farm to abattoir (5.8% versus 0.8%, respectively). This study demonstrates that resting pigs on the transport vehicle has the potential to decrease S. entericalevels entering the abattoir.

A series of four field trials were conducted to evaluate the ability of a cleaning and disinfection procedure in swine lairage pens to reduce the prevalence of Salmonella entericain slaughtered pigs. A cleaning and disinfection procedure was applied to lairage pens at a large Midwest abattoir. Each trial consisted of a cleaned (alkaline chloride detergent) and disinfected (H2O2plus peracetic acid sanitizer) pen (treated) and a control pen, each holding 90 to 95 pigs for 2 to 3 h before slaughter. Ileocecal lymph nodes, cecal contents, and rectal contents were collected from 45 pigs from each study pen at harvest and cultured for S. enterica. In all trials, cleaning and disinfection reduced the prevalence of S. enterica–positive floor swabs in the treated pen (P< 0.05). However, the postharvest prevalence of S. enterica–positive pigs varied between trials. In trial 1, there was no significant difference in the prevalence of S. entericain pigs between treatment and control groups. In trials 2 and 3, the prevalence of S. entericawas higher in pigs from treated pens versus pigs from control pens (91% versus 40%, P< 0.0001, and 91% versus 24%, P< 0.0001, respectively). In trial 4, the prevalence of S. entericawas lower in pigs from treated pens compared with pigs from control pens (5% versus 42%, P< 0.0001). This study indicates that cleaning and disinfection effectively reduces the amount of culturable S. entericain lairage pens, but the ability of cleaned and disinfected pens to reduce the prevalence of S. entericain market-weight pigs remains inconclusive.

In this study, we surveyed hogs (n= 300) as well as pork products (ground pork and raw chitterlings) for Listeria monocytogenes. Pig specimens collected before (tonsil swabs) and after slaughter (tonsils, lymph nodes, carcass swabs, and rectal contents) were examined for L. monocytogenesby enrichment with conventional enrichment broths followed by subculturing to selective agar. A multiplex polymerase chain reaction assay targeting the highly conserved 16S rRNA gene of the Listeriaspecies as well as the hlyAgene unique to L. monocytogeneswas used to screen aliquots of the enrichment (method I) as well as to confirm presumptive Listeriacolonies from Columbia agar with 0.05% glucose supplemented with polymyxin B-acriflavine-lithium chloride-ceftazidime-aesculin-mannitol (PALCAM; method II). Subculturing to PALCAM agar was the more sensitive of the two methods on the basis of the overall detection of Listeria. For hog tissues, method I detected L. monocytogenes(0.87% positive) and no other Listeriaspp. in all samples (n= 1,849). In contrast, method II detected significantly more (P< 0.05) L. monocytogenes(2.38%) and Listeriaspp. (0.38%) in these tissues. For small intestines (n= 300 raw chitterlings), L. monocytogeneswas identified in 8.3% of enrichments with University of Vermont modified Listeriaenrichment broth; plating to PALCAM slightly improved recovery (9%). Overall, ground pork samples (n= 340) harbored L. monocytogenes(45% positive) and other Listeriaspecies (1.5% positive), as determined by method I. Subculturing to PALCAM significantly (P< 0.05) improved the detection of L. monocytogenes(50.2%) but not that of other Listeriaspecies (1.7%). L. monocytogenesisolates (n= 243) were assigned to serotype 1 (53.5%), serotype 4 (25%), and serotypes other than 1 and 4 (21.4%).

The objective of this paper was to evaluate the effect of lairage (holding >12 h during transport to slaughter) in clean facilities on Salmonellaisolation 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 culture of Salmonella. Pigs were alternately assigned to a lairage treatment (holding in a clean, disinfected facility at the National Animal Disease Center) 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, commingled, and slaughtered. After slaughter, samples were collected for culture of Salmonella(feces from the distal colon, ileocecal lymph nodes, cecal contents, ventral thoracic lymph nodes, subiliac lymph nodes, and carcass swabs). Diaphragm sections were collected for serum ELISA. Salmonella entericaDerby 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 lymph nodes (43.6%, 119 of 273). There were lower Salmonellaisolation rates from the lairaged pigs (P< 0.05). The predominant serotype isolated at the abattoir varied by week of the study. This study suggests that pigs became internally contaminated with Salmonellaafter leaving the farm, possibly while in the abattoir holding pens, and that 18 h lairage, in clean facilities, does not increase shedding.