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Paratuberculosis, an endemic bovine disease in the French herd, will now be able to be "on the genomic radar" thanks to the deployment from this April of new genetic indicators of resistance, the result of an eight-year cooperation programme involving five partners, including BIOEPAR, within the Paradigm research consortium. For the time being, these new data only concern the Holstein dairy breed but should soon be extended to the Normande breed. By having earlier and more precise information on the resistance of animals to this silent disease, the symptoms of which often do not appear until adulthood, breeders and their advisers will be able to make the health monitoring plans set up in affected farms even more efficient. The combination of these health plans instructed by the Groupements de défense sanitaire (GDS) and genomic indicators obtained by genotyping animals will make it possible to optimise management strategies by predicting the level of resistance that individuals have.

Four sensitivity statuses and a "RPTB" pictogram

In a conventional setting, the monitoring of this insidious and complex disease requires numerous tests. The risk is that culling decisions are made too late, leaving time for the excreting animals to contaminate their environment. From 11 April 2022, genotyping of Holstein animals will determine their disease resistance status. Females will have four susceptibility statuses (highly susceptible, susceptible, standard, resistant). In the case of bulls from the Gènes Diffusion and Evolution selection schemes, a pictogram will indicate their paratuberculosis resistance status (PBR) for future generations, which is important information for breeders who are exposed to the disease, but also for the companies running the selection schemes. Animals that are too susceptible can be excluded from breeding. By making it possible to identify susceptible females, the genomic plan will integrate and reinforce the tools developed over the last ten years, which have already made it possible to obtain a status for each farm and to optimise screening. The health plans proposed by the GDS, the genomic indicators and the genomic mating plans proposed by the installation companies are more than ever complementary tools for reacting in a reasoned and proportionate manner to the increase and variability of exposure on farms.

What is paratuberculosis?

A disease that is difficult to understand at the herd level. - Paratuberculosis, also known as "white gut" disease, is caused by a mycobacterium similar to that of tuberculosis, which is very resistant in the external environment and sometimes persists in the microfauna (amoebae in drinking troughs, etc.). It is an inflammatory disease of the intestine which is always fatal. Although calves become infected through contact in the environment, only adult cattle are subject to the expression of the disease, which manifests itself as chronic enteritis, weight loss but without loss of appetite or fever. The complexity of the disease lies mainly in its detection, as not all animals excrete the bacteria at the same rate or with the same intensity, and its expression depends both on genetic factors and on the rearing conditions (feed, hygiene, density). 10% of cases are actually clinically visible. There is no treatment and vaccination remains imperfect.

A disease under surveillance, widespread in France. - Paratuberculosis is a disease subject to compulsory surveillance and notification and it is likely that its regulatory framework will be further tightened in the future. In fact, the proportion of affected dairy farms is within a wide but significant range, between 50 and 70%, mainly in the dairy sector. However, suckler farms are not free of the disease, particularly in the Limousin breed, where the GDSs also propose surveillance and sanitation plans and certification.

An economic impact for farms and industries. - Like any pathology present in a herd, paratuberculosis causes economic losses due to its impact on production (1 kg to 2.5 kg of milk per day, depending on the animal's level of contamination) but also, of course, on the herds when the animals die or have to be slaughtered prematurely. The whole process of monitoring, testing and culling procedures also mobilises financial resources. For a health protection group (GDS) such as those in the Grand Ouest, the cost is estimated at €250,000 per department per year. According to a projection established for a typical farm, i.e. 100 cows distributed on a representative scale of sensitivity and rate of infection (10 very sensitive with 70% infected; 20 sensitive with 30% infected; 50 standard with 10% infected, 20 resistant with 5% infected)*, the saving made over ten years is nearly €20,000 depending on whether the management is part of a classic health plan or a genomic plan.

More information from genomics

The key to genotyping. - As a knowledge accelerator, genotyping is now an essential tool for both the management of farms and selection programmes. For breeders, it represents an excellent decision-making tool for sorting females, applicable to different breeding strategies. For selection schemes, it is a sorting tool that has already proved its worth in the past, both for the management of genetic defects (CVM, HCD) and for genes of interest (hornless, red gene, casein, etc.). The fact that paratuberculosis is now being taken into account further strengthens its interest for all those involved in breeding.

The new genomic indicator of resistance to paratuberculosis is a world first.

Partners: 

• GDS France,
• Groupements de défense sanitaire du Grand Ouest,
• Fédération des entreprises de génétique et de reproduction des ruminants Allice,
• Institut national de recherche agronomique et de l’environnement (Inrae),
• Ecole nationale vétérinaire de Nantes (Oniris),
• Apis-Gene, société de soutien et de valorisation des programmes de recherche en génomique bovine, caprine et ovine.