Published on Wed, 05/26/2010 - 7:57am
Prevention is the key with Johne's. Even though symptoms of what we now know as Johne's disease were recognized as long ago as the 1800s, this costly infectious disease continues to challenge 21st-century dairy and beef producers.
What is Johne’s?
Johne’s (pronounced “yo-nees”) is a contagious disease of cattle and other ruminants that is caused by Mycobacterium paratuberculosis. Signs that cattle are infected include weight loss despite a normal appetite, chronic diarrhea and decreased milk production. Unfortunately, these clinical signs typically do not occur for two or more years after the animal is infected.
Infection most often occurs shortly after birth when calves swallow small amounts of infected manure from the udder or birthing environment. Other sources include bacteria passed in colostrum and milk, and in-utero transmission.
Because there currently is no effective treatment or vaccine, disease detection and management remain the best weapons in the battle against Johne’s.
A common disease
Sixty-eight percent of U.S. dairy operations are infected with Johne’s, according to the U.S. Department of Agriculture’s National Animal Health Monitoring System (NAHMS) Dairy 2007 Survey. While herds of all sizes have this disease challenge, prevalence is even higher in larger herds. However, the survey found no difference in Johne’s incidence based on geographic location.
The study cautioned that Johne’s likely is a problem in even more herds since environmental sampling – while effective – will not detect all infected operations
A huge cost
The NAHMS study also looked at how much Johne’s actually costs herd owners. The research showed a wide range based on the level of culling for this disease.
Infected herds with a low rate of culling animals that show clinical signs of Johne’s lost, on average, $40 per cow. On the other hand, herds that cull cattle due to clinical Johne’s disease symptoms at a higher rate lost an average of $227 per cow.
These substantial losses were due to a combination of factors, including reduced milk production, early culling, and poor conditioning at culling. The cost of Johne’s disease in beef herds still needs to be determined.
Does your herd have it?
Research suggests the chances are good that you have one or more infected animals in your herd – whether or not they show signs of the disease. But, the best way to know is through testing.
To start, work with your veterinarian to develop a surveillance program based on your testing objectives. Are you trying to determine whether Johne’s is present in your herd, to understand the extent of infection throughout your herd, to make a diagnosis on a sick animal, or to meet a purchase or shipping requirement? The answers to these questions will determine the type and timing of tests, the animals on which to focus as well as the interpretation of test results.
Assays that look for the M. paratuberculosis organism itself involve the testing of manure, tissue or environmental samples. Since the organism is so slow-growing, laboratory cultures must be monitored for weeks or months even though a heavily contaminated sample might show a positive result in a week or two. Manure-sample cultures can be conducted on individual animals or pooled samples from groups of five animals. Manure samples also can be analyzed using a polymerase chain reaction (PCR) assay. This test looks for the organism’s genetic material and can be used to confirm whether it is the Johne’s organism rather than a closely related “cousin.” The sensitivity is comparable to that of the culture.
Another type of test looks for antibodies produced by an infected animal, using blood or milk samples. The ELISA test is designed to evaluate large numbers of samples quickly (in a few days) at a low cost. The level of antibodies in each individual-cow sample is measured, compared with positive and negative controls, and then interpreted to create a numerical value – the higher the number, the greater the chance the animal is infected and shedding M. paratuberculosis. ELISA tests are available for both blood and milk samples. The AGID test also looks for antibodies, and is particularly useful when trying to diagnose a sick animal using a blood sample.
Animals to test
Due to the biology of M. paratuberculosis, only adult animals can produce the targets needed by diagnostic tests. So, even though cattle typically are infected when young, recommendations indicate cattle should be tested only once they reach 18 months of age.
Recent research also has looked at the phenomenon of “super-shedders.” Fecal-sample tests usually report results as low, medium or high. To qualify as “high,” the sample could have 50 colonies, 5,000 colonies or more. The University of Pennsylvania School of Veterinary Medicine found that about 10 percent of culture-positive animals are super-shedders, meaning they have at least 1 million colony-forming units (CFUs) per gram of M. paratuberculosis. The majority of super-shedder animals in the study were in good body condition, but their high levels of shedding could quickly contaminate feed, water and their environments.
Working with your veterinarian to develop a testing protocol and analyze the results is the best way to know your herd’s Johne’s status.
Almost one-third of U.S. dairy operations already participate in a Johne’s-control program, according to the 2007 NAHMS study. While this number is increasing, it is insufficient to truly control this insidious disease.
What should a Johne’s disease-control program include? Testing individual animals to identify those shedding is an important start since test-positive cows can contaminate the calving area – the prime location for disease transmission. To prevent calving-area contamination, test-positive animals should not be allowed in the maternity pen, or other areas where calves could be exposed and potentially infected.
Minimizing exposure of calves to manure from adult animals is easiest by removing them from the maternity area as soon as possible after birth. Then, house them by age and keep them separate from older animals.
Colostrum management also is key. Calves never should receive colostrum from an unknown source; while pasteurized colostrum is a consideration, it is critical that pasteurization be handled with care since colostrum has different properties and pasteurization requirements than milk.
Feeding a colostrum replacer, such as Colostrx 130 Colostrum Replacer, can be an important tool in helping eliminate the risk of transmitting diseases, such as Johne’s, through colostrum. In a University of Minnesota study, researchers found that plasma-derived colostrum-replacer feeding programs reduced the risk of M. paratuberculosis in Holstein calves born in Johne’s disease-endemic herds, implying that raw colostrum might be a source of Johne’s infection in calves.
If within-herd infection rates are high, culling all test-positive cows typically is not economically feasible. Test results coupled with an assessment of the individual animal’s value are helpful resources in developing a ranking for culling cows.
When bringing new animals into your dairy, be sure to observe at least minimum biosecurity measures to reduce exposure to manure and milk from cattle of unknown Johne’s status. Ensuring that new cattle come only from low-risk or known-status sources is an important start. Manage herd additions as higher-risk animals unless you have evidence to the contrary.
In some states, a vaccine is approved for limited use in controlling Johne’s disease. Due to issues surrounding its use, work with your veterinarian to determine whether this is a viable option for you.
More well-informed producers
The 2007 NAHMS survey also showed that 94 percent of dairy producers are familiar with Johne’s disease and understand basics about the disease – a marked increase from earlier surveys. Unfortunately, this increased awareness has not translated into improved Johne’s control throughout the country.
The key to managing Johne’s disease is to prevent new infections through improved biosecurity and adopting management practices that keep the disease from spreading within your herd.
Quick tips for reducing Johne’s disease
Since most new infections occur shortly after birth, calf hygiene is critical for prevention and control. These herd-management tips can help reduce the risk of Johne’s in your herd.
• Cows should always calve in a clean pen.
• Provide a separate maternity area for test-positive cows.
• Remove calves from the maternity pen as soon as possible after birth.
• Only cows testing ELISA-negative for M. paratuberculosis, the causative organism, should be used to supply colostrum for newborns.
• Thoroughly clean teats of colostrum donors before collecting colostrum.
• Administer to each calf at least four quarts of colostrum (three quarts for Jerseys) from one test-negative cow within four hours of birth.
• House calves away from the cow herd.
• Maintain good hygiene practices, especially in heifer rearing.
• Ensure that manure does not contaminate feed or water.
• Collect blood for Johne’s testing from lactating cows during the last third of their lactation.
• Cull all strong-positive testing cows before freshening.
• Visually identify all test-positive cows.
Special considerations when adding animals to your herd
It is far less expensive to block introduction of diseases like Johne’s into a herd than it is to control or eradicate the disease.
• Look closely at the source of new additions to your herd and buy from low-risk sources.
• Ask for health-test results.
• Isolate cattle coming into the herd.
• Implement biosecurity practices and animal-husbandry systems to prevent and control further infection.
Breaking the cycle of maternally transmitted disease
• Colostrum replacers can be particularly helpful when colostrum supplies are limited or of low-quality, or when you want to break a cycle of maternally transmitted disease – like Johne’s disease.
• Since the amount of globulin proteins a calf ingests during its first 24 hours of life directly affects its health, Colostrx® 130 Colostrum Replacer contains an industry-high 130 grams of globulin proteins in a single, two-quart feeding. This colostrum replacer comes in easy-to-use individual-dose packages, and contains consistently high levels of globulin protein derived from the same source that enriched natural colostrum.
For more information
Your veterinarian is the best resource for developing a Johne’s-control program that is right for your individual herd.
Additional sources of background information on this insidious disease include:
• USDA’s Animal and Plant Health Inspection Service: www.aphis.usda.gov/animal_health/animal_diseases/johnes/index.shtml
• Johne’s Information Center, developed by the University of Wisconsin School of Veterinary Medicine: www.johnes.org
• National Johne’s Disease Education Initiative: www.johnesdisease.org
• Johne’s Disease Veterinary Certificate Programs (by state): http://vetmedce.vetmed.wisc.edu/jdvcp/U.S.
• Animal Health Association’s Committee on Johne’s Disease: http://usaha.org/committees/jd/jd.shtml