Control of Salmonella in Market Hogs Using Immunization

Expected Benefits:
At present it is difficult to convince producers to pay for vaccination because there is no financial reward for producing Salmonella-free pigs but this research might be able to show a cost-benefit in terms of growth rate advantage.
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Summary of Research Results:
Clinical field trials were conducted to determine if salmonellosis could be controlled by vaccination. In trial 1, pigs were either vaccinated with a serotype isolated from the study farm (an autogenous bacterin made with Salmonella Typhimurium and injected intramuscularly), or vaccinated using a commercial live oral vaccine containing Salmonella Cholerasuis. A third group was used as unvaccinated controls. In trial 2, half the pigs were vaccinated with the S. Cholerasuis vaccine and half were unvaccinated controls. Trial 1 was conducted on a farrow to finish farm, and Trial 2 was performed on a multi-site operation. Salmonella shedding was not eliminated by vaccination. Pigs vaccinated with the autogenous bacterin did show a much greater drop in the prevalence of Salmonella shedding than the commercial Cholerasuis vaccine. The oral Cholerasuis vaccine was easier to administer but appeared to be ineffective in controlling Salmonella shedding in both trials. Salmonella shedding was associated with slower growth rate, even in the absence of clinical disease. This work contradicts earlier studies that suggested the commercially available S. Cholerasuis vaccines might provide sufficient cross-protection to be useful in controlling Salmonella infections on farm. The autogenous bacterin showed more promise but compliance would likely be a problem because of the significant labour required to inject vaccine to nursery pigs. It also might be expected that oral vaccine in addition to being easier to administer probably provides some degree of local gut immunity which is likely important in protecting the pig from infection. Future research should be directed to creating an oral S. Typhimurium vaccine because that serovar is the most common and is of importance from a public heath standpoint. The most significant finding in this trial is that growth rate might be improved if Salmonella shedding could be prevented. This provides an economic incentive for producers to implement Salmonella control measures. At present, unless producers notice clinical signs in their herd they are unlikely to consider any program directed at reducing Salmonella shedding.
<P> For more information, please visit the <a href="http://www.omafra.gov.on.ca/english/research/foodsafety/index.html&quot; target="_blank">Ontario Ministry of Agriculture, Food & Rural Affairs (OMAFRA) Food Safety Research Program</a>.