Salmonella entericaInfections in Market Swine with and without Transport and Holding

Abstract

The objective of this study was to compare, by using identical sample types, the Salmonella enterica prevalences and serovar diversities between pigs necropsied on the farm and those necropsied at the abattoir after transport and holding. We necropsied 567 market weight pigs (>70 kg) from six herds. Pigs were alternately assigned to be necropsied on the farm or at the abattoir. One-half of the group was sent in clean, disinfected trailers to slaughter at a commercial abattoir. After transport (mean distance, 169 km) and 2 to 3 h of holding in antemortem pens, these pigs were necropsied. The 50 pigs remaining on the farm were necropsied the following day. The same sample types and amounts were collected for S. enterica culture at both locations. Results show a sevenfold-higher (P < 0.001) S. enterica isolation rate from pigs necropsied at the abattoir (39.9%; 114 of 286) than from those necropsied on the farm (5.3%; 15 of 281). This difference was also observed for each individual herd. All sample types showed a significantly higher prevalence when comparing abattoir to on-farm collection, respectively: lymph nodes, 9.15 versus 3.6%; cecal contents, 13.6 versus 1.8%; 1 g of fecal matter, 25.2 versus 0.7%. Recovery of additional serovars at the abattoir suggests the pigs are receiving S. enterica from extra-farm sources. This study demonstrates that rapid infection during transport, and particularly during holding, is a major reason for increased S. enterica prevalence in swine. This finding identifies the holding pen as an important S. enterica control point in the pork production chain.

Impact of the Salmonella status of market-age pigs and the pre-slaughter process on Salmonella caecal contamination at slaughter

“…The mean number of serovars isolated per batch also increased between the farm and the slaughterhouse. These phenomena have been previously reported by Hurd et al [15,16] and McKean et al [21], who hypothesised cross-contamination in lairage.…”

“…Moreover, the lairage environment has been frequently found to be positive during the working day [31,38]. Whenever pigs waited in lairage at the slaughterhouse, an increase in the contamination rate was shown by studies which compared slaughtering on the farm and at the slaughterhouse [15,16]. A study carried out in 1987 also showed that contamination increased with the time spent in lairage, but the times compared (18 h, 42 h and 66 h) are very different from current reality [22].…”

“…However, the direct role of transport on Salmonella contamination was not clearly demonstrated. Lairage time has also been shown to increase Salmonella shedding before slaughter [15,16].…”

“…The effects of diverse factors, such as duration of fasting on the farm before loading [17,23], presence and duration of transport [16,17] and the conditions and duration of holding in lairage [14,31] were measured. To the best of our knowledge, no study has tried to observe the events occurring between the farm and the slaughterhouse in order to assess, without any intervention, the associations between suspected risk factors related to the preslaughter process and Salmonella contamination of caecal contents.…”

ModellingSalmonellaspread within a farrow-to-finish pig herd

“…Indeed, infected pigs do not exhibit clinical signs but do, however, shed Salmonella in their environment. They are then responsible for the contamination of susceptible pigs within the herd [7], during transport and lairage, and the contamination of carcasses during the slaughter process [4,14]. Focussing on reducing the number of Salmonella infected pigs at slaughter age can therefore lead to a reduction in pork food chain contamination 2 .…”