Johne's Module Overview
What is Johne’s Disease?
Johne's disease is a chronic, incurable bacterial infection that primarily affects the lower small intestine of ruminants, although the pathology and symptoms vary among species.
Infection occurs most when young animals ingest the bacteria Mycobacterium avium paratuberculosis (Map). After infection, the bacteria grow slowly inside the animal's intestinal cells. Over time, the animal’s immune cells multiply in response to the bacteria's presence, eventually leading to thickening of the intestine, impaired ability to absorb nutrients, and clinical signs of Johne's disease in some animals.
Clinical signs of Johne's disease are delayed because of a two- to six-year or more incubation period. Signs of late-stage infection include weight loss, intermittent or sudden unresponsive diarrhea, but a normal appetite. Some animals are unthrifty or develop "bottle jaw"—fluid under the jaw caused by protein loss. Late-stage animals continue to deteriorate and can die in a few days or a few months.
What Is the Economic Impact of Johne's Disease?
If many individuals in a herd become infected, control is difficult, and costly animal losses can be a drain on profits. Johne's disease in a herd is associated with some or all of the following costs:
- Premature culling resulting in increased replacement costs, increased cull rate, and loss of valuable animals and genetics
- Milk production may be decreased by 5 to 25 percent in the last lactation
- Decreased salvage value at slaughter owing to poor condition at culling
- Lost marketing and show opportunities
- Ineffective treatments and required drug withholding times
- Cost of testing and added management to prevent spread
A herd-level economic analysis of 934 herds in the Dairy '96 NAHMS study2 estimated that in herds where at least 10 percent of culled cows had clinical signs of Johne's disease, the average annual adjusted loss was $245 per cow in the herd. The average annual adjusted loss across all the positive herds in the study was $100 per cow and the extrapolated loss to the national dairy industry was $200 million.
How Does Johne's Disease Occur?
Herds are almost always initially infected by the addition of inapparently infected animals. In the herd, calves are most susceptible to infection. Resistance develops with age, although youngstock and even mature cattle can be infected if they receive high doses of or consistent exposure to the bacteria. Health, immune function, genetic resistance, nutrition, and strain of Map may also play a role in Johne's disease, but little is known about these potential factors.
Map can infect an animal in three major ways:
- Ingestion of manure in the calving environment that is from infected animals or from the cow's legs, udder, or teats.
- Ingestion of colostrum or milk from a cow that is in the later stages of Map infection. Feeding pooled colostrum or milk exposes more calves to this risk.
- Infection of the fetuses by Map organisms that cross via the bloodstream from the affected dam. This risk is less common but increases if the cow is in later stages of infection.
As infection progresses, the risk of transmission increases. Infected animals first shed Map in manure (stage II). Some may eventually disseminate it (stage III) to colostrum, milk, and the fetus and finally develop clinical disease (stage IV), shedding extremely large numbers of Map. In heavy shedders and clinical cows at slaughter, Map has been cultured from colostrum and milk samples from up to 35 percent of these cows and from 20 to 40 percent of their fetuses. Recovery of Map was much lower from samples from subclinically infected cows: from 9 percent of colostrum samples, 3 percent of milk samples, and 9 percent of fetal tissue samples.
Although they are not major causes of infection, bull semen, embryo transfer, and wildlife are other proposed routes that should not be overlooked.
When Does Clinical Johne's Disease Develop? Age and Dose Dependent
Clinical disease in cattle typically does not occur until maturity. Calves infected at a young age with a high dose of organisms, however, may develop clinical disease at less than two years old. The total number of clinical cases and the occurrence in two-year-old’s, sometimes even younger animals, will grow as infection in the herd becomes more extensive.
Animals exposed at an older age (18 to 24 months or older), or to a very small dose at a younger age, are less likely to develop clinical disease. If they do develop it, it will occur later in life. Onset of clinical disease is often associated with stressful conditions such as calving, dry period, extreme temperature or environmental stress, feed changes, nutritional imbalances, relocation, or concurrent diseases.
What Are the Stages of Johne's Disease Infection in Cattle?
Early, silent, subclinical, nondetectable infection. This stage is typical in youngstock less than two years of age and animals exposed to a low dose of Map or at an older age. This infection cannot be detected with fecal culture or serologic tests (ELISA). It progresses slowly, over months or years, to stage II. Some animals may resolve this early infection or simply never progress to the next stage.
Subclinical shedders. Typically, this stage occurs in older youngstock and mature cattle in which infection has progressed. Animals appear healthy but shed intermittently so that Map may or may not be detected on fecal culture. Fewer than 10 percent have enough antibody to be positive by an ELISA blood test. Risk of transmitting infection is less than at stages III and IV, but a high proportion of infected animals in a herd are in stage II, so they are a hidden source of infection.
Intermittent, early clinical signs, heavy shedders. These animals may either appear healthy or have diarrhea or weight loss. They are likely to be detected through fecal culture and ELISA. Map is found in high numbers in manure and at lower levels in some animals (10–35 percent) in colostrum, milk, and the fetus. These animals are a high risk for transmitting infection.
Clinical Johne's disease, heavy shedders. Cattle in advanced infection classically have diarrhea, lose weight, produce less milk, and continue to eat. Signs often coincide with stress events. Occasionally, animals appear to recover but relapse after a subsequent stress event. Stage IV animals shed billions of Map in their manure, and circulating organisms are likely to be present in colostrum, milk, and the fetus. These animals are hazardous to the rest of the herd. They are "heavy shedders" on fecal culture, many are positive on serologic tests, and they are an enormous source of infection and premise contamination. This terminal stage may last a few days to months if animals are not culled. Moreover, carcasses may not pass inspection.
"The Johne's Iceberg"
In a herd where Johne's is established, every cow in stage IV represents several cattle in earlier stages. The distribution of infected animals in infected herds resembles an iceberg (Figure 1). Thus, the clinical case (stage IV) of Johne's disease in a home-raised animal represents only the "tip of the iceberg" of infection in the herd. The number will vary depending on the degree and spread of infection in the herd, but 5 to 20 other animals may be infected for each clinical case. A single fecal culture test in a herd detects only 30 to 40 percent of infected animals, and 20 to 30 percent of these individuals will be in stages III and IV, shedding high (>106 colonies/gram feces) numbers of Map. The remaining 70 to 80 percent will be in late stage II, shedding lower (<103) numbers of Map.
The iceberg illustrates the how Johne's disease is a hidden herd problem, which if ignored can fuel an increasing rate of new infection in each generation. Diagnosing and preventing Johne's before multiple clinical cases occur is the most effective way to prevent a widespread and costly infection.
How is Johne's Disease Detected in Cattle?
There are two primary types of diagnostic tests that look for either the organism that causes Johne's disease (MAP, Mycobacterium avium subspecies paratuberculosis) or the animal's response to infection by MAP) antibody in the blood). Organism-detection based tests include 1) PCR which looks for the MAP genetic material from living or dead MAP, and 2) Culture, which isolates the living MAP organism itself from manure, tissue, or environmental samples. PCR has largely replaced culture as the most accurate and affordable way to detect MAP.
Fecal PCR on individual animals is used on manure samples. The assay looks for MAP's genetic material instead of the living organism. Results are provided in 7–10 days. The accuracy of culture and PCR are comparable with the PCR being faster and less expensive.
Pooled fecal culture is an accurate and affordable way to test a herd if that herd has a low prevalence of infection. Individual manure samples are collected them the lab will combine 5 samples in one pool for culture. If a pool is positive for MAP, the individual samples will be tested individually with the PCR test to confirm which animal(s) in that pool is shedding MAP.
Environmental Culture is used to screen herds for MAP with unknown status. Six composite samples from common cow areas are collected at one time to represent a commingled sample of all adult cows in the herd. Common sites that represent the herd include prefresh, calving and sick pens; common lanes or alleys, congregation points such as feeding areas and fresh manure collection. If MAP is found, there is no correlation with prevalence of Johne's in that herd and individual testing would be the next step. If no MAP is found, this does not guarantee Johne's is not present so repeat environmental testing every 6 months is recommended.
Serology tests, such as the ELISA, measure the concentration of antibodies to MAP and are less accurate but faster and less expensive. They identify cattle with elevated antibody (stages III and IV) and are best used to screen herds or groups for presence of infection. ELISA’s are less sensitive than PCR and culture, detecting roughly one-third of the animals that the PCR and culture will identify as MAP-infected. ELISA tests can produce false positives from cross-reaction with other organisms, so PCR testing of positives to confirm shedding of MAP is recommended.
In general, Johne's disease tests fail to detect more than 50 percent of animals infected with MAP and serologic tests can be expected to give some (1-3%) false positive results. Nevertheless, Johne's tests are good tools and can be an important part of Johne's disease control when used in conjunction with good management practices. An appropriate herd management plan should be developed in consultation with the herd veterinarian and a diagnostic laboratory approved for Johne's tests by NVSL. The NYSCHAP Johne's Disease Herd testing Reference Manual should be reviewed before a testing strategy is chosen.
When and which animals to test
Test Adult Animals
Due to the biology of MAP infection, only adult cattle (18 months and older) produce the targets needed by diagnostic tests. That is, calves are infected while very young, but they do not shed the organism with any frequency (so the organism detection assays will be negative) nor do they produce antibody (so the blood/milk tests will be negative). That is why it is recommended that diagnostic tests be used only for animals at least 18 months old.
Recommended Testing Approaches
There are a variety of ways to test your herd that will give you the information that you need. The best testing program can be developed by you and your veterinarian since you know your operation best: its goals, resources, other animal health issues, etc.
Here are some approaches that have worked well for other beef cattle owners. Think about what you are trying to accomplish and then look at our recommendations:
Is MAP present in my herd? Options for testing:
- Targeted testing (ELISA or fecal culture) of oldest or thinnest cows (10% or more of the herd).
- Whole herd test. You can save money by only testing cattle 3 years and older.
- Culture or PCR on 6 environmental fecal samples collected where cattle concentrate such as around feeders or waterers. Refer to Cornell
What percentage of my cows are MAP-infected? Options for testing:
- A good estimate can be made by blood testing (ELISA) all cows that have calved twice or more.
- If you are confident the infection rate is low, PCR on pooled fecal samples is a good choice.
What test should I use to control MAP in my infected herd? Options for testing:
- Blood testing (ELISA) on cows that have calved twice or more.
- PCR on individual culture that have calved twice or more.
- Test clinically ill (thin or with diarrhea) cattle. See the Control section for further information.
What test should I use to eradicate Johne's disease in my herd? Options for testing:
- PCR on all cattle 18 months and older one month before calving season with all PCR-positive animals either culled or segregated well away from the main herd. Repeated annually until three negative tests are achieved on the herd.
Does this skinny cow have Johne's disease? (Making a diagnosis for a sick cow: weight loss, diarrhea) Options for testing:
- PCR on a manure sample if previous cases have been seen in the herd.
- Necropsy. This has the advantage of helping to discover any and all possible causes of illness, not only Johne's disease. Tissues should be collected and submitted to a diagnostic laboratory for histopathology and PCR (ileum and mesenteric lymph nodes).
What test should I do before buying or leasing an animal? Options for testing:
- This is usually negotiated between the buyer and seller.
- Occasionally local regulations made specify the type of test.
- From the seller's perspective a single low-cost low-sensitivity test only the specific animal(s) involved is preferred, i.e., ELISA on a blood sample (a negative test is more likely).
- From the buyer’s perspective, a negative whole-herd test using the most sensitive test (PCR on manure samples from individual cows) is preferred as this maximizes likelihood the any animal from the herd is not MAP-infected.
What Should I Do about Controlling Johne's Disease on My Farm?
Implementing a preventative program is always less expensive and easier than controlling Johne's disease. Producers should think about managing for Johne's routinely, similar to the way they handle other familiar herd infections such as Staph aureus and Strep ag mastitis, foot warts, or E. coli calf scours. The best approach to Johne's disease is to have a plan and make it part of the routine. Learning more and discussing the prevention points with a veterinarian is a good place to start.
There are three key elements to prevention and control of Johne's disease:
Do Not Introduce Infected Animals into the Herd
Johne's is virtually always introduced to a herd by addition of inapparently infected carrier animals. Producers who buy animals should assess their biosecurity risk and the potential impact of introducing several diseases: Johne's, BVD, Strep ag, Staph aureus, Mycoplasma mastitis, infectious foot diseases, Salmonella, and Neospora. Risk of introduction can be reduced by knowing the source, requesting a history of health status and management programs for specific diseases, buying from lower-risk sources, initially isolating animals—particularly from youngstock—and instituting prevention practices.
Institute Preventive Risk Management Practices
Routine management practices that prevent the most susceptible animals—those less than 12 months and preferably up to 24 months—from ingesting Map in manure, colostrum, milk, feed, and water are the most critical element in control of Johne's disease.
Identify Infectious Animals
Spread of Map infection can be dramatically reduced by identifying and "removing" the most infectious animals by culling, segregating, or managing them differently. Recognizing and testing suspect animals should be a standard policy. Herd testing added to management, can help further in breaking the cycle.
The specifics and relative importance of various control and prevention measures will be different for each farm situation. For example, to break the cycle in infected herds, control programs must focus on hygiene and husbandry. In contrast, the top priority for uninfected herds is prohibiting entry by any infected animal. In both cases, an appropriate testing strategy can make the plan more aggressive.
Producers must also make a long-term commitment to Johne's control; thus, herd plans must fit their current and future goals and resources. Each farm must decide what is necessary to control Johne's. The important risks must be identified and then managed by realistic, routine procedures. And, from the start, plans should involve the employees who will be responsible for carrying them out.
Critical Management Points for Johne's Herd Plans to Reduce New Infections
The following principles can be adapted to dairy and beef operations:
Manage Manure (“All Manure Is Guilty”)
- Prevent exposure of newborns to Map at calving by ensuring that calves are born in a clean, dry area that is used only for calving. Put cow-calf pairs on clean pasture.
- Provide youngstock with clean feed and water that is not contaminated with manure, especially from older animals.
- Raise youngstock in separate facilities or segregated from mature cattle and their manure.
Manage the Risk in Colostrum and Milk
- Feed colostrum from healthy cows, preferably ones that test as low risk. Minimize pooling; feed one cow’s milk to one calf to reduce risk further.
- Use milk replacer, milk from healthy, low-risk cows (preferably those that test is low risk) or pasteurized whole milk. Minimize pooling.
Identify and Manage Infectious Animals
- Observe, diagnose, and take aggressive action on clinical suspects and high-risk animals. Segregate and cull immediately.
- Adopt a test strategy and use a result-based decision plan to manage high– and low-risk animals: cull, segregate, or manage to reduce the risk of infecting replacement animals. Coordinate test results to be available for critical decisions such as drying off, calving, breeding, pasture use, culling and replacement selection.
- When adding animals, consider the status and potential impact of Johne's in the home herd, and investigate the magnitude of risk in the source.
- Develop and integrate a Johne's management plan with other farm priorities and resources; identify responsibilities; put the plan in writing; regularly evaluate its effectiveness and modify it as needed.
The NYSCHAP Johne's Disease Program
NYSCHAP can help identify the risks for the introduction and spread of Johne's Disease on dairy farms. Working with the herd veterinarian and farm managers, the Agriculture and Markets field veterinarian can assist in developing and reviewing a herd plan to deal with and prevent these risks. By writing out the farm plan and assigning responsibility for the specific practices to farm personnel, being part of a program increases the likelihood that the preventive practices will be implemented, and that progress will be made toward the farm's Johne's control goals. NYSCHAP focuses on best management practices and, if testing is part of the herd plan, offers a discount on Johne's testing performed at the Cornell University Diagnostic Laboratory.
NYSCHAP encourages farms at low risk of infection to consider pursuing test negative status through the NY Johne's Herd Status Program.
How to Enroll in NYSCHAP
To enroll in NYSCHAP, contact your herd veterinarian. They will then make arrangements with the regional field veterinarian from the Department of Agriculture and Markets. For additional information, contact one of the sources below:
- To enroll or contact a state field veterinarian, call NYS Division of Animal Industry at 518-457-3502
- For diagnostic testing services or information, call the Diagnostic Lab at Cornell University, 607-253-3900
- For mastitis testing or information, call Quality Milk Promotion Services at 607-255-8202
- For general information call the NYSCHAP coordinator
- Visit the NYSCHAP website for more information and contact information