Dairy industry and researchers work to reduce prevalence of Johne's disease
Canadian researchers and the dairy industry have set their sights set on reducing Johne’s disease in cow herds.
Johne’s disease is widespread within the dairy industry. Ontario’s Ministry of Agriculture, Food and Rural Affairs estimates that 20 to 30 percent of dairy herds have cows infected with Mycobacterium avium subspecies paratuberculosis (MAP), the bacteria that causes Johne’s disease. Alberta Milk puts that number at 50 per cent or higher.
The exact number of infected cows is impossible to determine as diagnostic tests only detect the disease if the animal has developed antibodies. Dr. Gerald Ollis, formerly Alberta’s chief provincial veterinarian, says that 95 per cent of animals infected will never show symptoms.
There are no effective vaccines or treatments for Johne’s. Infected cows don’t conceive as quickly as healthy cows and produce less milk. In the later stages of the disease, they shed billions of bacteria each day, which can easily infect replacement heifers. There has been speculation (so far unproven) that MAP may be linked to Crohn’s disease in humans. Animal health agencies are now banning, or thinking of banning, imports of livestock from countries without a Johne ’s disease management program.
The dairy industry in Alberta has launched a voluntary herd risk management program that focuses on decreasing the spread of Johne’s disease. The program is based on the Canadian Johne’s Disease Initiative, and is supported and endorsed by ALMA and Alberta Milk. Under the program, dairy producers work with veterinarians to assess their herd’s risk for Johne ’s disease. Producers can then take practical steps to reduce the spread of the disease within their herds, such as sanitizing bottles and making sure calves don’t come into contact with cow manure. There's more information on the program in the YouTube video below.
Researchers hope to unlock genetic resistance
Meanwhile, researches at the University of Guelph and University of Alberta are trying to find the key to genetic MAP resistance.
Researchers studied six commercial dairy herds in Ontario. All the dairy herds had a history of MAP infections. From those herds, they found 232 Holsteins infected with MAP. By genotyping these cows, researchers identified at least 12 chunks of DNA that may include genes influencing MAP resistance.
Some of these genes were found near other regions that previous research had identified as influencing resistance to other diseases, including mastitis (currently being studied by researchers at the University of Alberta). Of course, other researchers have also found that genes associated with disease resistance seem to flock together. My post from last week mentioned that resistance to pink eye, foot rot, and shipping fever seemed to be associated with a location on chromosome 20. Those same researchers are now looking at genetic resistance to Johne’s disease.
Exactly what role these genes play in resistance to Johne’s disease still has to be worked out. So far researchers have only established a possible link between genes in these 12 regions and resistance. Once those links are confirmed and better understood, researchers hope that they can analyze variations within the genes to figure out how to make cattle more resistance to MAP.
Between the research being done on disease resistance and the dairy industry’s work to manage the disease, dairy producers should eventually gain ground against Johne’s disease.