Johne's Disease
The infection occurs in the layer of cells of the digestive tract that are responsible for absorption. This area becomes thickened as the body’s immune system attempts to control the infection. The thickening prevents the digestive tract form absorbing nutrients which creates a chronic diarrhea that does not respond to treatment and subsequently leads to a loss of body condition in spite of a normal appetite. There is no cure for Johne’s. Animals that develop clinical signs will eventually die from the disease. Clinical signs usually do not develop before 2 years of age. However, the range is 6 months – 12 years with 5 years as the average. The long incubation period of this disease makes it a herd problem as well as an individual animal problem. Many animals can become infected before any in the herd show clinical signs. The primary way any herd becomes infected with Johne’s is through the purchase of infected animals.
What causes Johne’s Disease?
What are the Clinical Signs of Johne’s Disease?
Because of the slowly progressive nature of the disease, cattle can be infected for years before exhibiting clinical signs. Some infected animals may never exhibit clinical signs in their normal productive life times. While cattle exhibiting clinical signs shed the highest numbers of MAP, most infected animals will shed large numbers of MAP sporadically in their manure for months or years. The result is a “Tip of the Iceberg” phenomenon, where many animals in a herd can be infected with few or any showing clinical signs: One infected cow showing clinical signs can indicate 1-2 more cows sick, but not yet obvious (clinical), 6-8 cows infected, but not yet sick (sub clinical) and 10 to 15 infected calves and young stock that may develop the disease later on in life.
How Does Johne’s Disease Enter a Herd and How Does it Spread?
Calves are far more likely to become infected when exposed than older animals. Young stock less than 6 months of age are the group at high risk for infection. Within this group, calves less than 1 month of age are at the highest risk. In young calves, the intestine is designed to be more “open” to allow the development of immunity to many pathogens. Unfortunately, it is believed this creates an easy route of infection for MAP. In order to prevent the spread of infection within a herd, it becomes critical to prevent exposure of calves to manure, colostrum and milk from infected cows. Although calves are at the highest risk of infection, it is important to remember that all age groups can become infected if the exposure is high enough. Preventing the contamination of feed, water and bedding with MAP for the entire herd is critical in preventing the spread of Johne’s.
The Manitoba Picture
Why is the Prevention and Control of Johne’s Disease Important?
Significant losses as a result of poor production occur in herds that have had clinical cases. In US dairy herds that had greater than 10% of their culls showing clinical signs, there were 707 kg (1559 lbs.) less milk per cow per lactation. In these same herds, the annual adjusted value of dairy production that is $227.00 less per cow than average. Overall, US herds that have a history of Johne’s disease have losses of $100.00 – $200.00 USD per cow annually compared to those herds that do not. A recent study involving Ontario herds found that test positive cows had 2% - 6% less milk production. This represents 173 kg (381 lbs.) – 548 kg (1208 lbs.) in a 305 day milk production. There was also an indication of less fat and protein production from test positive cows. This study indicated a 3 fold increase in culling rate for test positive cows. The overall loss per cow for each herd was $123.00 - $195.00 CAD. Sub clinical infections with Johne’s disease are also significant for beef production. Recent studies suggest that test positive cattle are slower to gain weight after calving and produce calves that have both lower birth weights and lower rates of gain while nursing the cow.
Of great concern are the potential losses associated with consumer confidence in meat and milk safety. The clinical signs of Johne’s disease have some similarities to Crohn’s disease in humans. Crohn’s disease is a type of inflammatory bowel disease, an incurable chronic inflammation of the intestinal tract that occurs in people 15 – 35 years of age. The major symptoms include weight loss and diarrhea. The cause or causes are still unknown. Any evidence linking the 2 diseases remains inconclusive at this point. What is known is that the incidence of Crohn’s and Johne’s is increasing. Some researchers have cultured MAP or have identified MAP DNA from a proportion of Crohn’s patients. Other researchers have been unable to duplicate these results. Studies in food safety have been done to determine if MAP could be cultured from pasteurized milk or meat. Again the results are inconclusive, with some finding MAP and others not. Currently, there is not a consensus within the medical community as to the significance of any association between the 2 diseases. Health officials do not recommend any changes in diet. The beef and dairy industries are based on the provision of healthy, wholesome products to consumers. Should a causal link be made between the 2 diseases, the resulting impact on consumer confidence is something producers should take very seriously.
How is Johne’s Disease Prevented or Controlled Within a Herd?
Test and cull programs that worked well for diseases such as Brucellosis are not effective for Johne’s disease. Testing for Johne’s disease, while important to estimate the level of infection on a herd level, is not accurate enough to test and cull individual animals. The prolonged incubation period means that infected animals under 2 years of age will not likely test positive. Infected adult animals will not always be at a stage in the disease to register a positive result. A combination of testing and the implementation of specific management practices are essential to prevent and control Johne’s disease.
Currently, fecal culture is the “gold standard” test. It is expensive, time consuming and can provide false negative results because an infected animal may not be shedding MAP when the sample for culture was taken. A positive fecal culture means the animal is definitely infected and shedding MAP in manure, but 55% of infected animals (who are likely not shedding) will culture negative.
ELISA tests that determine the level of antibodies (immune response) to MAP in either milk or blood are rapid, inexpensive and easy to do. They are almost as good as fecal culture at determining negative animals. However, they are only able to determine 28% to 61% of the culture positive animals. By extrapolation, these tests are only able to determine 10% - 30% of the actual infected animals in Johne’s positive herds.
The use of specific management practices are the most important way to control and prevent Johne’s disease. The best practices are those that prevent exposing young calves to infected manure, colostrum, or milk. The following can be considered critical control points for Johne’s prevention.
- Limit the purchase of replacement and breeding stock as much as possible. When purchasing stock, it is best to buy younger animals from herds that have implemented a Johne’s control program. If purchasing older animals, testing should be considered in spite of the limitations.
- Cull infected animals: Cattle that exhibit clinical signs or are fecal culture positive should be removed from the herd as soon as possible.
- Provide special handling of suspect cattle – those that test positive to an ELISA test or are relatives of clinically affected cows.
- Suspect cattle, if they are to stay in the herd, should not be housed in group calving pens, hospital pens or with young stock. This would include pastures.
- Calves from these animals should receive colostrum from a negative source and be removed from the dam immediately.
- Make sure these animals are marked in a way that makes them easily identifiable. Notched ear tags or different colored tags are methods that can be use.
- Keep calving areas clean and dry: Reducing the exposure of new born calves to manure is critical in preventing the disease.
- Calving areas can be quickly assessed by kneeling down on the bedding pack. The pack should be dry and bedded enough to prevent the knees from getting wet. Regular cleaning of maternity pens with the use of lime will help.
- For beef herds it is best to provide calving areas separate from wintering areas.
- For dairy herds, it is best to provide a separate calving area from the dry cow group.
- It is important to not use maternity pens as hospital pens.
- Keep calves segregated: While unrealistic for beef herds, this is an essential practice for dairy herds.
- Calves should be raised separately from mature animals until they are ready to calve. Take care to prevent manure run off and splatter from adult cattle from contaminating the feed, water, and bedding areas of young stock.
- 'If possible, calves should be removed from their dams immediately after birth. If removal is not possible, then procedures that prevent exposure to manure in the calving pen and on the udder should be implemented.
- Colostrum from negative and / or younger cows is preferred; younger cows are less likely to be shedding MAP. Alternatively a dried commercial colostrum product or pasteurized colostrum can be used.
- Feeding raw milk or waste milk is not recommended. High quality milk replacer is preferred. Otherwise feed only pasteurized milk or milk from negative cows.
- Prevent manure contamination of feed and water:
- As much as possible, use separate equipment for feeding and manure handling. Otherwise, implement procedures that allow for cleaning of equipment between the different uses.
- Care should be taken to not travel through feeding areas with tires, boots or equipment covered with manure.
- Prevent animals from walking through feed or water areas. Fence line feeding, raised feed bunks and feed barriers that allow only the head and neck of the animal access should be utilized. Dug outs, swamps and natural ponds should be fenced off to prevent manure contamination of the water supply.
- Separate waterers and feed bunks are preferred for young stock. Prevent manure build up around waterers and feed bunks.
- Do not allow grazing in the same season as manure application. Keep stocking rates on pasture as low as possible.
- Keep facilities clean and handle manure properly:
- Clean corrals, cattle sheds, barns and holding pens frequently. Ensure that drainage from these areas do not contaminate feed or water.
- Store manure in areas where cattle do not have access. Proper composting is believed to reduce MAP in manure. However, this has not been fully investigated.
- It is preferable to spread manure on crop land. If manure is applied to hay or pasture land, do not use in the same season.
Implementing a prevention and control program for Johne’s disease requires a long term commitment. It is important to maintain and review the plan once it is in place. If your herd is considered to be low probability of having Johne’s, it is still important to implement the control points listed above. This will help minimize spread if the disease is introduced and will help control for other diseases, such as calf scours.