Impact of commercial preharvest transportation and holding on the prevalence of Salmonella enterica in cull sows

The objective of this study was to examine the prevalence of Salmonella enterica in cull sows at various stages from the farm to the abattoir. Cull sows (n=181) were sampled over 10 weeks. Fecal samples (10 g each) were collected on the farm ca. 24 h before loading and at the live-hog market ca. 3 h before loading. Samples (ileocecal lymph nodes, cecal contents, feces from the transverse colon, ventral thoracic lymph nodes, subiliac lymph nodes, sponge swabs of the left and right carcass sections, and chopped meat) were collected at the abattoir. The percentages of positive fecal samples on the farm and at the live-hog market were 3% (5 of 181 samples) and 2% (3 of 181 samples), respectively. After transport from the live-hog market (10 h) and holding at the abattoir (6 h), 41% (74 of 180) of cull sows yielded S. enterica in one or more sampled tissues. The isolation rate for total cecal contents (33%; 60 of 180 samples) was significantly (P<0.05) higher than those for ileocecal lymph nodes (7%; 12 of 181 samples), feces (11%; 20 of 181 samples), and ventral thoracic and subiliac lymph nodes (2%; 4 of 181 samples). Before a 2% lactic acid carcass wash (lasting 8 to 9 s), 14% (25 of 180) of carcasses were positive, compared with 7% (12 of 179) after the wash (P<0.05). Two S. enterica serotypes, Derby and Infantis, were found on the farm and at the live-hog market. At the abattoir, 12 serotypes that had not previously been found on the farm or at the live-hog market were recovered. The results of this study demonstrate that transport and holding practices may contribute to an increase in S. enterica infection prior to slaughter to levels much higher than those found on the farm.