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Research review: Are some cows genetically susceptible to Johne’s disease?

Published on 02 June 2021

A research project led by Nathalie Bissonnette at Agriculture and Agri-Food Canada (AAFC) – Sherbrooke and Kapil Tahlan at Memorial University in Newfoundland is investigating genetic markers in dairy animals that may be associated to Johne’s disease susceptibility or resistance.

The project, “Unraveling the genetic susceptibility to Johne’s disease,” is financed by AAFC and Lactanet with in-kind contributions by Holstein Canada under the Dairy Research Cluster 3.

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For dairy farmers, this disease results in financial losses related to reduced milk production, decreased pregnancy rates, increased premature culling and impacts overall animal welfare. Economic losses in the Canadian dairy sector resulting from Johne’s disease were recently estimated at $21.5 million to $34.1 million.

The main pathogen that causes Johne’s disease is Mycobacterium avium subspecies paratuberculosis (MAP). Management tools are currently in place to reduce the spread of Johne’s disease in Canada. For example, by implementing the Biosecurity module of proAction, dairy farmers work with their veterinarians to mitigate the risks of introducing existing and emerging animal diseases on their farms to maintain the health of the herd. However, controlling Johne’s disease is difficult due to the disease’s unpredictable progression and the weak sensitivity of diagnostic tests.

Previous research has shown the potential to reduce the prevalence of Johne’s disease in cattle by selecting for animals genetically resistant to the disease. This innovative application would be complementary to the tools farmers can use alongside management strategies to prevent infections.

Over a five-year period, Bissonnette and her collaborators collected serum and fecal samples from 3,150 cows. The team used this data combined with other diagnostic tests to define a classification system and identify animals as either infected and infectious, infected and assumed resistant or healthy. Using this unique dataset, they were able to accurately model the development of Johne’s disease over time and correctly differentiate between cows that would eventually develop Johne’s disease and those that resisted the infection and did not excrete the pathogen.

The researchers are also genotyping cows using two proven genetic testing methods (i.e., single nucleotide polymorphisms [SNP] panel and genotyping-by-sequencing) and analyzing the epigenetic profile of susceptible cows. So far, the team has identified genetic and epigenetics markers associated with the susceptibility of developing Johne’s disease.

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In recent publications, the researchers confirmed the presence of genetic modifications and the epigenetics effects are associated to Johne’s disease.

Analysis was performed to study the markers in vitro and studying immune tolerance to Johne’s disease using bovine primary macrophages. Further research on a second population of dairy cows is ongoing and will confirm the usefulness of the genetic markers for selection of Johne’s disease resistance/tolerance.

The team is also investigating the genetic diversity of MAP strains by using validated tools and classifying the variants from animals across Canada infected with Johne’s disease at different stages. These analyses will define which factors affect the performance of diagnostic tests and explain disease progression. This ongoing work to identify MAP variants that could be more virulent will be key for the development of a successful vaccination program in the future. end mark

References omitted but are available upon request. Click here to email an editor.

Canadian Dairy Research: For a profitable, innovative and sustainable sector

Dairy Farmers of Canada (DFC) invests in research to stimulate productivity, sustainability and profitability on farms and to improve knowledge on milk and dairy products’ health benefits. DFC finances research initiatives that benefit all dairy farmers across Canada and works in collaboration with its members and other sectorial partners to address farmers’ priorities set in the dairy research and knowledge translation, and transfer national strategies. Visit Dairy Farmers of Canada - dairy researchDairy Farmers of Canada - dairy research for more information.

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