What’s the deal with Salmonella Dublin in Ontario?

By Katherine Perry, MSc and Dr. Dave Renaud, Associate Professor, University of Guelph

Salmonella Dublin (S. Dublin) has been increasingly discussed as an emerging problem facing the dairy, beef, and veal industries in Ontario. Although it has been difficult to quantify how big that problem was, as it had only been sporadically identified at premises across the province.

New research from the University of Guelph aimed to change this by improving our understanding of S. Dublin in Ontario. This research focused on S. Dublin presence at Ontario dairy farms, and additionally identified management practices or herd-level factors that increased the risk of S. Dublin presence in a dairy herd.

But first, what is S. Dublin?

Salmonella Dublin is a type of bacteria that is host-adapted to cattle and can also elicit infections in humans through direct contact with animals or raw/under-cooked food. Associated outbreaks on cattle farms are characterized by high morbidity and mortality rates – usually marked by symptoms of respiratory disease and sudden deaths in young calves. Animals that survive the initial infection can then become chronically infected, continuing to shed bacteria into the environment through milk and feces without visible symptoms. To make matters worse, most strains of S. Dublin identified in Ontario are largely resistant to commonly used antimicrobials, which contributes to why S. Dublin infections can lead to devastating economic losses for producers and animal welfare challenges.

What is the status of S. Dublin in Ontario?

Initially identified in 2012, S. Dublin had since been isolated from laboratory sample submissions across Ontario dairy, beef, and veal farms. A new study was conducted where a convenience sample of 100 Ontario dairy farms were visited to characterize S. Dublin infections and identify management practices that increased the risk of S. Dublin identification in the herd. The research team collected blood samples from 20 heifers aged four months to two years old, as well as a bulk tank milk sample. Researchers identified S. Dublin from at least one blood or bulk tank milk sample at 25 of the 100 Ontario dairy farms visited.

Although, this prevalence was not generalizable to all of Ontario, due to the methodology of the study. Which is why the researchers conducted another study that aimed to estimate the prevalence of S. Dublin across Ontario dairy farms. Based on one bulk tank milk sample collected from every commercial dairy farm in Ontario, the research team estimates that S. Dublin is present at 4.5 per cent of dairy farms in Ontario. However, the research suggests that this number could be higher if youngstock were sampled.

What might put dairy herds at risk?

An important aspect of both of these studies was identifying some management practices or herd-level factors that might be associated with an increased likelihood of S. Dublin positivity.

In the study evaluating 100 Ontario dairy farms, five practices were associated with an increased risk of S. Dublin identification: introduction of animals from outside the herd, allowing cattle to temporarily leave the herd and return (such as cattle shows, embryo collection centers or loan to other dairy farms), and poor calving area hygiene. This included practices such as infrequent addition of bedding material to calving pens, frequent removal of manure from the surface of bedding in calving pens and allowance of greater than three cows per pen in the calving area.

The larger study that investigated S. Dublin at every commercial dairy herd in Ontario also identified herd-level factors that might increase the risk of S. Dublin presence at the farm. An increased likelihood of S. Dublin identification was observed at dairy herds located in Western Ontario, those with greater than an average of 102 total cows, farms with higher average 305-day milk production as well as those with higher average somatic cell count measures.

What does this mean for veal farmers?

Current research suggests that S. Dublin is an emerging concern in Ontario, and it is present at a number of dairy farms across the province. Laboratory sample submissions also indicate that S. Dublin is present at several Ontario veal operations. The animal health challenges, and economic losses associated with S. Dublin, should be a considerable driver for preventing S. Dublin from entering and spreading within veal farms. When purchasing calves from other farms, veal producers could consider ensuring that animals or their source farms are negative for S. Dublin and speak with your herd veterinarian for additional ways to mitigate your risk.

This research was funded by Dairy Farmers of Ontario and the Ontario Ministry of Agriculture, Food and Rural Affairs.