Johne's disease (pronounced YO-neez), or paratuberculosis, is a chronic intestinal infection in cattle and other ruminants caused by the bacteria Mycobacterium avium paratuberculosis, or MAP. The bacteria initially reside in the last section of the small intestine – the ileum. Over time, often over several years, the number of bacteria grows and the animal’s body responds with inflammation. All this causes the intestinal wall to thicken until it is unable to absorb nutrients. As the disease progresses, the bacteria may also spread to other tissues, including lymph nodes, uterus, and mammary tissues. Bacteria are shed in manure, colostrum, and milk to become a source of new infections.
Although MAP does not replicate in the environment, it is hardy and has been shown to survive up to 9 months in manure pits, 11 months in soil, and 17 months in water.
Herds infected at low levels can experience decreases in production and overall cattle health long before specific symptoms are apparent. Herds infected at high levels have animals with signs of disease, further decreases in production, and cattle loss that may threaten the industry.
Transmission
The main way the disease spreads is when animals eat or drink feed and water contaminated with MAP. Infected calves, cows, and bulls shed the bacteria in their manure, contaminating the environment, including feed and water. Feed troughs, hay bunks, water tanks, ponds, stagnant water, maternity pens, and group pens can become contaminated directly from an infected animal or indirectly from equipment or people tracking manure on tires, boots, clothing, etc.
Newborns and young animals can ingest the bacteria from manure as they are being born, in the maternity pen, or on the dam. Colostrum or milk from infected cows is also a source of infection. Infected dams, especially if they are showing symptoms, can pass the disease on to their unborn calves.
Newborn calves or young animals are the most susceptible to infection. While animals develop some resistance with age, individual animals of any age can be infected if there are enough bacteria in the environment, feed, or water. All breeds of cattle, both dairy and beef, can be infected.
The number of animals showing symptoms does not reflect the total number of infected animals. For every animal showing symptoms, there may be 10 to 25 others infected. This is why you may see one case of clinical disease every few years, and then suddenly find 10 percent or more of your herd showing advanced signs.
Prevention & Control
Whether you raise purebred seedstock, grade seedstock, or production animals, you need to have a Johne's disease herd plan. The specifics and intensity of a herd plan strategy will vary. To be effective, it must fit your immediate and long-term goals for your farm within available resources. You can't begin too soon. The vital tools are prevention, management, testing, culling, and in some cases, vaccination.
Prevention & Management
We have worked with the University of Wisconsin-School of Veterinary Medicine to develop online producer and veterinary training programs to use in getting started with your Johne’s disease control program. Talk to your herd veterinarian about completing a Johne’s disease risk assessment for your farm and developing a Risk Assessment and Herd Management Plan (RAMP). The RAMP is designed to reduce your risk of introducing Johne’s disease onto your farm and to maximize your efforts in controlling it if already there.
Culling
Effective culling requires good herd records and individual animal identification. Your specific operation and herd goals, resources, etc. will help determine when and whether a test-positive animal will be culled. Working with your veterinarian to develop an individualized herd plan will help you to make decisions on whether and which animals to cull.
There is a vaccine against Johne's disease that is given to calves up to 35 days of age. It is one tool for heavily infected herds. Research has shown that the vaccine reduces the number of animals with clinical disease, reduces (but may not eliminate) the amount of bacteria shed into the environment, and eventually can reduce (but may not eliminate) the number of animals becoming infected. Expect the best results if you use the vaccine along with herd management that reduces Johne’s disease transmission.
Wisconsin Johne’s Disease Control Program
This program is voluntary for cattle and goat producers – both dairy and beef/meat. The goal of the program is to provide standards for the control of Johne’s Disease.
By participating, you will:
- Improve your understanding of Johne’s disease and its impact on your bottom line;
- Learn and implement Best Management Practices that can help prevent and control Johne’s disease in your herd;
- Learn and implement Best Management Practices that can help prevent and control the spread of Johne’s disease to your customers’ herds; and
- Have the opportunity to achieve a Classification Level that shows your customers your commitment to helping prevent and control the spread of Johne’s disease to their herds.
Currently there is no reimbursement for costs incurred in managing Johne’s disease.
Clinical Signs of Illness
Obvious symptoms, or clinical signs, in cattle include weight loss (even with a normal appetite) and diarrhea. The diarrhea may come and go, or may eventually become chronic, and does not respond to treatment. Many animals produce less milk than expected. Some animals may develop a low grade fever and, as the disease progresses, swelling under the jaw. Once symptoms appear, death occurs in weeks to months.
Clinical disease (presence of symptoms) has been seen in animals as young as 6 months and as old as 15 years. Symptoms often don't show until the first or second lactation or later, even though animals often become infected when calves. Age when exposed to bacteria; amount of bacteria to which exposed; stress caused by factors like calving and moving to new barns; and genetics all appear to play a role in when an animal shows symptoms.
Many cattle have "subclinical" infections. They may not show symptoms of diarrhea or weight loss, but they may not perform as well as expected. For example, they may produce less milk, or they may be more susceptible to problems such as infertility and poor health. Animals with subclinical infections can still shed bacteria and serve as a source of infection to others.
Because Johne's disease is a hidden disease, testing can be a useful part of a management plan. Testing alone, however, is not enough to control or eliminate Johne's; you need management, too. Consult your herd veterinarian to develop a herd testing strategy that is right for you BEFORE you test and then follow your plan.
A few reasons to consider testing:
- Management benefits: By knowing an animal’s test status, you can minimize exposure of susceptible animals.
- Economic benefits: Knowing the test status of herds from which you purchase reduces your risk of buying Johne’s disease. If you sell cattle and your herd is test-negative for Johne’s disease, you may be able to market animals for a premium.
- Legal benefits: You may be liable if you sell an infected or exposed animal as if it were healthy.