Submitted to: Pig Veterinary Society International Congress Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 6/5/2002
Publication Date: 6/5/2002
Citation: ROSTAGNO, M.H., HURD, H.S., MCKEAN, J.D., ZIEMER, C.J., GAILEY, J.K., LEITE, R.C. SALMONELLA INFECTION IN MARKET SWINE DURING PRE-SLAUGHTER HOLDING. CONGRESS OF THE PIG VETERINARY SOCIETY. 2002. P. 319. Interpretive Summary:
Technical Abstract: A significant increase in the proportion of Salmonella-positive pigs when comparing prevalences at the farm and after slaughter has been demonstrated by several studies. Transportation and holding of pigs prior to slaughter have been linked to increased Salmonella prevalence at the abattoir, which has been attributed to the effect of stress and reoccurrence of shedding. However, the effect of pre-slaughter holding, where close contact with other pigs and environmental exposure occur may be an important determinant of Salmonella prevalence at slaughter not only through the effect of the associated stress, but also as an infection source. The objective of this study was to determine if the holding pens can serve as a significant source of Salmonella infections for swine prior to slaughter. Three repetitions of the experiment were executed at two high capacity abattoirs (16,000 pigs/day). Each repetition included 4 groups of pigs (~ 150 animals/group). For each group, pooled fecal samples were collected from the transport trailer right after the pigs were unloaded (pre-holding samples). The holding pens were sampled prior to the pigs entering for the pre-slaughter holding (holding samples). After slaughter, cecal contents and ileocecal lymph nodes were collected from 30 pigs in each studied group (post-holding samples), randomly selected in the slaughter line. All samples were processed by conventional bacteriological methods for the isolation and identification of Salmonella. From the 24 transport trailers sampled, 20 (83.3%) were Salmonella-positive. All holding pens sampled (24/24) were contaminated with Salmonella, and in 8 (33.3%) of these holding pens, drinking water samples were Salmonella-positive. All groups of pigs studied (24/24) were Salmonella-positive in the post-holding samples, including those from Salmonella-negative transport trailers. Overall, 43.8% of the samples collected from transport trailers, and 76.4% of the samples collected from holding pens were Salmonella-positives. There was a significant difference (p < 0.05) between abattoirs in the total number of holding pen positive samples (62.5% and 90.3%). From the 24 groups of pigs studied, 25% were infected with Salmonella serovars that matched serovars isolated from the respective transport trailers, 25% were infected with serovars that matched with serovars isolated from the respective holding pens, and 45.8% were infected with serovars that matched with serovars simultaneously isolated from the transport trailers and holding pens. The average number of Salmonella serovars found was 1.6 serovars/transport trailer, 3 serovars/holding pen, and 3.7 serovars/group of pigs. Of the total number of Salmonella isolates from post-holding samples (n = 969 isolates), 15.7% matched with serovars isolated from pre-holding samples, 25.8% matched with serovars isolated from holding samples, and 7.9% matched with serovars isolated from pre-holding and holding samples simultaneously. Results from this study demonstrate that abattoir holding pens are frequently contaminated with a variety of Salmonella serovars. It is likely that pigs become infected during transportation and pre-slaughter holding, through cross-infections and exposure to a contaminated environment. Our results indicate that the contaminated environment of the holding pens is probably the major source for Salmonella infections for swine prior to slaughter.