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Sometimes Johne's is obvious.
Sometimes it isn't
What is Johne's disease? Johne's (pronounced "yo-knees") is a contagious bacterial infection primarily of the lower small intestine. Also known as paratuberculosis, Johne's most often infects dairy and beef cattle, sheep and goats. The disease has also been reported in captive and wild free-roaming ruminants, such as whitetail deer.
How do animals become infected? Johne's spreads primarily through ingestion of feed or water contaminated by manure from infected animals. Infected dams, which may or may not be exhibiting signs, can pass the disease to calves while nursing through their colostrum and milk. Because of its mode of spreading, Johne's must be considered a herd problem, as well as an individual animal problem.
What are the clinical signs? Obvious clinical signs of Johne's include weight loss, diarrhea and lower milk production. Some animals continue to eat normally. Diarrhea may begin intermittently then progress to chronic, usually without a fever. Some infected animals appear unthrifty and have a swelling under the jaw. These signs are similar to other diseases and conditions, making a veterinarian's diagnosis necessary. Symptoms usually first surface when an animal is two years old, following a physical stress like calving. However, visible signs of Johne's may not appear for 10 years or more. The age of the animal at exposure and the number of bacteria ingested determine when the symptoms of the disease develop. Research indicates animals maintained under better feed and husbandry conditions tolerate infection better.
Why do some animals not show clinical signs? Infection may not be apparent in many animals that have not yet advanced to Stage 3. The absence of obvious symptoms illustrates why Johne's is considered a silent disease. In unculled herds, all cases of Johne's ultimately progress through the four stages of development until the animal dies:
Stage 1 is silent, subclinical and non-detectable. Infected calves and animals younger than two years of age, or those exposed to a small dose of bacteria, which do not show symptoms, are in this category. Current testing is unable to detect Johne's in this stage.
Stage 2 animals are generally older heifers or adults that may appear healthy. However, these subclinical shedders are passing enough organisms in their manure to be detected by fecal culture test. These animals pose a risk to others in the herd by contaminating the environment.
Stage 3 animals have visible symptoms of Johne's. They have acute or intermittent watery diarrhea, weight loss, and a drop in feed efficiency and milk production. Intermittent signs at this stage usually progress to more severe infection. These animals will likely test positive on blood and fecal culture tests.
Stage 4 is the end of the disease process. Most animals appear very thin, with fluid diarrhea. Animals may progress from Stage 2 to Stage 4 in just a few weeks.
How is Johne's diagnosed? The best detector of Johne's is a fecal culture test. This method is slow-requiring 12 weeks to 16 weeks of culture time in the laboratory. New technology developed at Purdue University* can reduce culture diagnostic time to 4 weeks to 8 weeks. Blood tests, while less accurate than culture, are faster and less expensive. Blood testing can be used most effectively to confirm clinical cases or to test a group of animals in a herd. Neither method is an effective test for very young animals. Johne's disease is most accurately diagnosed by examining the lower small intestine and associated lymph nodes in a dead animal.*Developed by Ching Ching Wu, D.V.M., Ph.D.; Purdue University
Is a Johne's disease vaccine available? A killed vaccine is available for use only in cattle herds under a special agreement of the State Veterinarian, producer and herd veterinarian. The vaccine will not prevent an animal from becoming infected. It will reduce the outward signs and prolong an animal's useful life. Use in high-incidence herds is thought to be beneficial. If the incidence is very low, the best solution is to attempt to control the disease by testing, and removing positive animals. More information on the use of vaccine as part of a herd management plan is available from a veterinarian or the Office of the State Veterinarian.
What if animals test positive? Because Johne's-infected animals cannot be treated, they should be sold to slaughter as soon as possible. This may not be practical economically, if a large number of animals are involved. Proper management is the most effective tool available for preventing, controlling and eliminating Johne's. Review the document, Guidelines for Johne's Disease Eradication, to read more about eradicating Johne's disease from cattle herds.
A management strategy should be based on the number of infected animals in the herd. The management plan must be designed to minimize economic impact while eliminating the disease. The plan must be written to spell-out the responsibilities of the veterinarian, producer, employees and others involved with the herd. Over time, the plan will require modifications.
Separation of young and old animals must be complete to prevent the spread of Johne's disease. Animals in this photo are not properly separated.
How can herd management control Johne's?While Johne's is best managed within a herd by age group, several principles apply to all groups in all herds.
Newborn and Very Young CalvesNewborn calves are highly susceptible to bacteria shed by older animals. Organisms are found in the bedding of calving pens, on the walls, alleyways and on the dam. Preventing the spread early is an excellent time to begin a control program.
The calving area must be kept very clean and dry. The calving pen should only be used for calving by one animal at a time. The calf should be removed immediately from the dam, because she may be shedding bacteria. Some calves become infected in the womb; separation from the dam cannot prevent this spread. Infected beef dams and calves can be isolated until the cow can be salvaged and the calf placed in a feedlot for slaughter-only.
Some dams shed the bacteria in their colostrum and milk. Negative-testing dams should be selected as sources of colostrum. Milk replacer is recommended in highly infected dairy herds.
Young Breeding Stock Separation of young breeding animals from older stock must continue as they mature. Greater distances and longer separations from older, infected animals decrease the likelihood of infection. When field isolation is not possible, walls, panels, or double fences can create barriers or buffer zones. Young animals should not be pastured on forages after adults or allowed to drink water run off near those areas. Leftover feed from older adults should not be fed to young breeding stock. Feed must be provided in feeders which prevent fecal contamination. Manure from older animals should not be spread on pastures.
Mature Animals Management of adults includes preventing the spread of the infection from one animal to another by preventing exposure to manure of infected animals. Highly infectious waste can be eliminated by testing adults and selling all positives to slaughter as soon as possible. Manure from test-positive animals contains billions of Johne's bacteria. These cattle are sources of infection for others in the herd, especially calves and younger breeders.
A whole-herd test is beneficial to evaluate how many animals may be infected. Rapid removal of positives after frequent testing will shorten the course of the herd disease, as well as the opportunity for further spread. Early culling also maintains higher salvage values of positive animals. Earlier diagnosis also slows the spread of disease-causing bacteria. Culling only clinically ill animals will not control the disease.
Separation of old and young animals without sanitation will not accomplish control of Johne's disease.
Johne's Prevention Human, animal and equipment traffic between groups should be avoided. People can spread Johne's bacteria on boots, clothing and machinery. Frequent and thorough removal of the manure from the stalls is important to prevent exposure through contaminated feces. Any accumulation of manure is a potential source of infection to animals of any age. Manure should be spread only on field crops, not pastures.
All feed must be provided in feeders that prevent fecal contamination of the feed. The same equipment should not be used to handle feed and remove manure. Human and animal traffic in the feed bunks must be prevented. Animals drinking from standing pools of water and run off, as well as creeks and streams, can ingest Johne's bacteria shed by other animals.
Livestock of unknown status should not be allowed on the farm. All new breeding animals must spend adequate time in quarantine, then be retested before joining the herd. Buyers need to ask for a negative Johne's test and herd history before buying animals. Producers should seek out herds tested for one or more years, or those granted special status by a state's Johne's committee.
What are the economic costs of Johne's? The economic impact of Johne's varies widely from herd to herd. The number of animals involved and how long the disease goes undetected are major factors which determine the course of the disease.
Dairy producers generally see the effects of Johne's in their herds more quickly than do beef producers. Milk production may drop as much as 1500 pounds per cow. As the disease progresses, animals lose weight and produce fewer pounds of lower-quality milk. Increased culling and higher mortality also contribute to the economic drain on the infected farm.
A low-Johne's clinical herd (fewer than 10 percent of cull cows showing symptoms) results in about a $40 milk-loss per animal; the loss climbs to $227 in high-Johne's clinical herds (those with greater than 10 percent of culls with signs). DHIA records report about $243 profit per head for the same year.
Failure to recognize the progression of Johne's prevents early, aggressive culling of infected animals, which is needed to reduce the contamination and exposure within the herd. Culling of animals, before the disease progresses to advanced stages with a severe loss of body condition, will provide greater salvage value and less loss to the owner. The median price received for culls in good condition is reported to be about $400; $250 per head for those in poor condition.
These losses also interfere with the development and selection of genetic replacements. Reports indicate a lot of breeding animals are sold out of infected herds. Increased culling rates and the lack of readily available genetic selection results in increased replacement costs. This can vary greatly, depending upon their source and quality, but probably will be close to $1100 per head.
Veterinary expenses will also be greater in infected herds. The additional diagnosis, testing and consultation fees will negatively impact a herd's potential to return a profit.
Producers can calculate the loss incurred from Johne's by filing in the corresponding blanks in the Cost of Johne's Disease to Dairy Producers brochure. If you would prefer a free copy of the booklet please contact BOAH.