Johne’s disease can increase feed costs and reduce cow longevity. There has also been long-standing speculation that the organism that causes Johne’s may also
be associated with Crohn’s disease in humans. Researchers have not established a conclusive cause-and-effect tie between the two diseases, and to the best of our knowledge, neither the World Health Organization nor any individual nation has declared Johne’s to be a zoonotic disease (a disease that can impact both animals and humans). Despite this fact, misinterpreted and misguided information can have serious consequences for the beef industry.
Johne’s disease (pronounced “Yoknees,” also known as paratuberculosis) primarily affects cattle and other ruminants, but has also been reported in swine, carnivores and non-human primates. Cattle with symptoms of Johne’s disease were first reported in Germany nearly 200 years ago. Since then, the disease has been found throughout the world. The bacterium that causes Johne’s disease (Mycobacterium avium subspecies paratuberculosis, or MAP) was discovered over 100 years ago.
Young calves are believed to be the most susceptible to infection, but symptoms of Johne’s disease normally do not develop until cattle are mature. In the meantime, MAP hides from the immune system, multiplies in the intestinal lining, and damages the cells that absorb nutrients. Infected cattle eventually develop chronic diarrhea, lose weight, get thin, and eventually die. Calves are exposed to infection through the cow’s manure, udder, colostrum, milk, straw, water and feed. Adult cattle may be susceptible to infection if they are exposed to high levels of MAP. MAP does not multiply in the environment, but it can survive in manure, water and pastures for at least five months in Canada.
Johne’s disease is believed to be more common in dairy than beef herds. Researchers have estimated that from one to two per cent of mature Canadian beef cows and two to nine per cent of Canadian dairy cows may be infected with Johne’s. The total numbers however may not be all that different since Canada has four or five beef cows for every dairy cow. The discrepancy in Johne’s disease incidence may be related to differences in housing and calf management, but the important point for the beef industry is that although some cows start their careers by producing milk, most end up producing beef.
The symptoms of Johne’s disease in cattle are similar to those of human Crohn’s disease, and MAP has been isolated from some Crohn’s patients. This has led some scientists to suspect that MAP may play a role in both diseases. Other scientists argue that patients who are severely ill with Crohn’s disease are more susceptible to infection by many other organisms, including MAP. Following long-standing scientifitradition, this argument has been played out in hundreds of published research papers for nearly a century, and has still not been conclusively settled.
VACCINATION, TREATMENT AND DIAGNOSIS OF JOHNE’S DISEASE
Efforts to eradicate Johne’s disease have been unsuccessful for three reasons. Firstly, the Johne’s disease vaccines that have been developed do not provide complete protection. As a result, infected animals will not appear to be sick but will still shed MAP. Secondly, Johne’s disease cannot be treated; antibiotics licensed for use in cattle do not kill MAP. Thirdly, Johne’s is very difficult to diagnose accurately, especially in the early stages of infection. The diagnostic tests that are currently available do not reliably detect many infected animals until they are shedding large numbers of MAP. As a result, efforts to eliminate Johne’s disease using “test-and-cull” methods have been unsuccessful. By the time an animal is confirmed to be infected, it has had the opportunity to spread the infection to other susceptible animals in the herd. The beef and dairy industries continue to invest in research to develop better vaccines and detection methods, because effectively overcoming these shortcomings would greatly improve our ability to combat the disease effectively.
THE CANADIAN JOHNE’S DISEASE INITIATIVE
There are clear risks for consumer confidence and international trade if the potential link between Johne’s and Crohn’s disease is confirmed. To ensure that Canada is less vulnerable to these risks, Canada’s beef and dairy industries have developed a new program to combat Johne’s disease, even though current vaccines, treatment and diagnostic options are not ideal. This initiative is led by the Canadian Cattlemen’s Association (CCA), Dairy Farmers of Canada (DFC), and the Canadian Animal Health Coalition (CAHC), with expert input from Johne’s disease researchers and support from the federal and some provincial governments. The beef program is focused on disease prevention, which can be summarized in three simple points.
1. Preventing Johne’s disease has broad benefits: Management changes that decrease the risk of Johne’s disease will also reduce exposure to other, more common calfhood diseases (particularly calf scours), improve the effectiveness of vaccines for calfhood diseases, and improve overall herd health, performance and effi- ciency.
2. Prevent the spread of Johne’s disease: Johne’s disease is primarily spread through infected manure or infected colostrum. Keeping the calving area as clean and dry as possible is very important so that the most vulnerable calves are protected. In beef cattle, Johne’s disease is mainly spread from mother to calf, through infected colostrum, milk, or udders. Cows that show symptoms of Johne’s disease should be removed from the breeding herd,
along with their daughters. Responsible management of stock water, grazing, manure and run-off can further reduce the possibility of spreading Johne’s disease to other cattle, neighbouring herds, wildlife and the environment. The degree to which wildlife can spread Johne’s disease is unclear, but the MAP bacterium has been shown to survive in soil and water for several months, where it could potentially reinfect
new animals. 3. Don’t buy or borrow Johne’s disease: Do not obtain replacement breeding stock or colostrum from herds that are suspected or known to carry Johne’s disease. Only purchase commercial colostrum supplements from a company that uses production methods that destroy MAP.
As with most outcome-based strategies, prevention and control measures will not be a one-size-fits-all solution. The measures that are most important on one farm may not be necessary or cost effective on another. To help cow-calf producers identify the most cost-effective measures for their operation, cattlemen will need to work with a trained veterinarian to examine the herd’s Johne’s disease history, conduct a risk assessment of current management practices related to the spread of MAP, and develop a plan to implement the most appropriate measures to minimize Johne’s disease in that particular herd.
Successful adoption of on-farm management practices that effectively control and prevent Johne’s and other common calfhood diseases will reduce the need for therapeutic antibiotics, and improve herd health, animal welfare, performance and efficiency. Ultimately, this will contribute to the reputation of Canada’s beef industry as a supplier of the world’s healthiest, safest, high-quality beef. For more information on the Canadian Johne’s Disease Initiative, visit the CJDI page on the Canadian Animal Health Coalition website at http://www.animalhealth.ca/CJDI/.