52 It’s Farming. And It’s Better. Better Farming | April 2024 Livestock Davidson explains that from a surveillance perspective, samples tend to focus on herd-level results rather than the individual animal. This is made more complicated by the length of time required for seroconversion, the time between pathogen exposure, and the appearance of antibodies for Salmonella Dublin infections. “Most of the time, when you get exposed to a pathogen, you can test for antibodies in a matter of weeks,” says Davidson. “When talking about Salmonella Dublin, the seroconversion time is seven weeks, which is a really long time.” This means that while calves are most susceptible while they are young, the best time to test for previous exposure is between four to six months of age. Renaud says that in Ontario, current surveillance efforts focus on bulk tank sampling in dairy herds. A similar approach was taken in British Columbia, with more repeated samples collected than Ontario. Studies from Renaud’s lab also investigated risk factors associated with positive results for Salmonella Dublin at the herd level. Recent surveillance results, which Davidson says found that seven per cent of bulk tank samples were positive for Salmonella Dublin, suggest that prevention of transmission is extremely important for naïve herds that have not yet been exposed. Managing on-farm Canada does not currently have any approved vaccines for Salmonella Dublin, which means hygiene and good biosecurity are the best strategies to avoid the disease. “Currently there are no vaccines specifically for Salmonella Dublin available in Canada. There are vaccines for other strains of Salmonella, but it is currently unclear whether they provide any cross-protection,” explains Gillies. Renaud’s research identified herd-level risk factors for Salmonella Dublin, which emphasizes areas of focus for prevention of transmission. Based on these risk factors, farmers should: prioritize calving area cleanliness and minimize manure; avoid having more than three cows in a maternity pen as it increases the chances of having a positive cow in the calving area; avoid buying in cattle, loaning out cattle, or sending them to shows, with the risk being sending cattle off-farm and bringing them back into the herd. The main route of transmission to calves is fecal-oral. Davidson explains that this commonly occurs in the calving pen. “It seems that the calving pen is the highest risk area,” says Davidson. “The cow calves and then the calf takes a nosedive into the contaminated pen. It is also dose-dependent – the more the calf is exposed, the sicker it’ll be.” Keeping calving areas clean should be a priority for keeping calves healthy. Maintaining a closed herd, particularly in those still naïve to Salmonella Dublin, will also reduce the risk of bringing in the bacteria with Improve hygiene by cleaning housing and shared equipment. Diane Kuhl/iStock/Getty Images Plus photo
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