October 2023 Issue


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Johnes (pronounced Yo-nees) is a contagious disease that can infect all species of ruminants. Of unknown origin, Johnes is found world wide, is a significant problem in confined dairy cattle, and was first diagnosed in goats in the early 1900's. Johnes causes a "wasting condition" in goats, but is not the same thing as the prion-based Chronic Wasting Disease found in other species.

Caused by the organism Mycobacterium avium paratuberculosis (MAP), Johnes is a chronic infection that establishes itself in the small intestine, causing a thickening of the intestinal wall which prevents the normal absorption of nutrients. The goat is reduced to using its fat and muscle reserves to survive, resulting in starvation. Goats can contract both the sheep and cattle strains of Johnes. In goats, the symptoms do not appear until the last stages of the illness.

The bacteria is passed from goat to goat via fecal-to-oral contact as well as the dam's milk. Fecal-contaminated teats can infect suckling kids. Young kids are the most susceptible, and the disease remains unidentifiable for years after the kids have first ingested infected feces. Severe weight loss in adults is the only symptom.

Johnes Disease is unknown to many goat breeders because of the elusive nature of the disease. More cases of Johnes are being diagnosed. Dairy cattle operations have long been fighting Johnes, and people raising goats on land that formerly housed dairy cattle are seeing Johnes appear in their goats.

The first symptom is usually significant weight loss. In addition to weight loss, other symptoms include lack of appetite and depression, occasionally but not always followed by diarrhea. Goats infected with Johnes frequently are more subject to heavy parasite loads. Assuming overcrowding and filthy facilities don't exist on the farm, any adult goat with continuing heavy barberpole wormload should be tested for Johnes Disease.

Recognizable signs of this disease do not appear until goats are yearlings and sometimes much later. Kids can contract Johnes in utero (before birth) if their dams are heavily infected. Kids can also become infected through the colostrum and milk of Johnes-positive mothers. This bacterium is hardy and heat resistant. Pasteurization can kill most (if not all) of the organisms, depending upon the concentration of the bacterium in the milk, and may be a useful technique for reducing (but not eliminating entirely) the infection level in kids. Johnes can live for years in the soil and surrounding environment.

How soon the disease becomes evident in a herd is based upon how concentrated and how heavy the dosage of bacteria the goat ingested, the age of the goat, and its genetic makeup. If a kid receives a high dose at an early age, the kid will most likely begin shedding the disease in its feces and showing clinical signs of infection at an earlier age than a kid who received a low dose of the bacteria. Some goats are carriers and never show clinical signs of the illness. There may be an age-related resistance to Johne's Disease, but older goats can also become infected, particularly in overcrowded and unsanitary conditions.

Obvious signs of infection usually begin to appear only after many years of shedding the bacteria, particularly if the animals are managed well, with good nutrition, clean conditions, no overcrowding, and minimal stress in their lives. Once it is evident that infection is present, Johnes-infected goats usually live less than one year and ultimately die from their inability to absorb nutrients from their intestinal tracts.

The timeline roughly runs from birth to age one, no signs whatsoever; from age two to four, goats may begin to show signs of some weight loss but have no decrease in appetite until the disease becomes full-blown; and goats over age four who are heavily-loaded with the bacteria begin to look wasted. The mid-stage, from approximately age two to four, is the dangerous time, because those goats look reasonably well but are heavily shedding the bacteria.

There are three commonly available tests for diagnosing Johne's Disease. None of these tests are 100% accurate.

Culturing fecal matter to detect the organism is possible, but the bacteria grows slowly, taking the test six weeks to complete. If the number of bacteria in the feces is low, it is possible that not enough will survive to produce a positive culture, even though the goat is infected. If the culture shows the presence of the MAP bacteria, the goat is absolutely positive.

The Polymerase Chain Reaction (PCR) test detects the genetic material of MAP in feces, but the number of bacteria, especially in recently-infected animals, may be so low that there is not enough DNA to be detected. The PCR test is 40-45% accurate in light shedders and 95-98% accurate in heavy shedders. Most labs now use a test that combines culture and PCR. In this test, feces is cultured for 24 hours to increase the number of bacteria followed by PCR to detect the bacteria's DNA, resulting in a faster and more sensitive diagnostic. If the animal being tested is not shedding the organism in its feces, it can test negative even though it may really be infected. Repeat testing on suspect goats is essential.

False positives rarely occur with the PCR test, allowing you to find out which goats are shedding the organism on your premises. The PCR test also tells other important information, such as how much of the organism is being shed.

The AGID (Agar-Gel Immune Diffusion) test and the ELIZA (Enzyme-Linked Immuosorbent Assay) test detect antibodies and are done on blood samples. Each test has its own shortcomings.

Sensitivity of the AGID Test (ability to detect small amount of antibody) is much lower than the ELIZA Test and can produce false negatives, but specificity is high, so there are few false positives.

The ELIZA Test is very sensitive (detects small amounts of antibody) but can cross react with the bacteria that causes Caseous Lymphadenitis (CL) and give a false positive. To be accurate, the ELIZA test must be species specific, i.e. it must use components specific for goats if the blood sample if from a goat. Unfortunately, some labs are using bovine (cattle) components when they test goats, which can result in false positives. The ELISA Test works best as a herd-screening tool with positive samples confirmed by PCR/Culture.

I recommend having Bob Glass of Pan American Vet Lab (512-964-3927) do the ElISA blood test, and if Bob's results indicate further study, then contact the Wisconsin Vet Diagnostic Lab at the University of Wisconsin-Madison (1-800-608-8387) or another lab that does PCR testing to have a Direct PCR test done on the goat's feces. Most of the research on Johnes has been done at the Johnes Center at the University of Wisconsin under the direction of Dr. Michael Collins. Information is available online, but the internet links seem to change more often than phone numbers.

Think of the disease as a pyramid. For every animal which tests positive, there are probably 10 animals who are infected, actively shedding, and not showing symptoms. This does not apply if an infected animal is brought into a clean, closed herd, unless the circumstance is not discovered and properly managed. Then it takes some time for this pyramid to build up, but it will occur.

There is no cure for this disease, there is nothing that can be put into the soil and the surrounding environment to kill the bacteria, and the only vaccine for Johnes is made in Australia. The vaccine is not and will not be available in the United States because it cross-reacts with tuberculosis (TB) tests. A disease with similar symptoms occurs in humans called Crohns, but researchers have never been able to establish a connection between Johnes in ruminants and Crohns in humans. Johnes is not believed to be transmissible to humans. Meat from Johnes-infected goats is safe for human consumption.

Managing fecal-to-oral transmission is the key to controlling Johne's Disease. Raise all feeders. Use a footbath from pen to pen. Keep manure from contact with kids. When moving feed troughs, pitchforks, water containers, and shovels from pen to pen, wash and bleach them thoroughly first. "All manure is suspect."

Much of the literature used in the preparation of this article was furnished by Bob Glass, President of Pan American Vet Labs, Lexington, Texas (near Austin). Pan American tests for CAE and CL, in addition to providing Johnes testing. Contact Bob via email for further information at bglass@pavlab.com.

Suzanne W. Gasparotto , Onion Creek Ranch, 10/1/23

Subscribe FREE now! Monthly issues with new articles and other educational information on meat goat health, nutrition, and management written by Suzanne W. Gasparotto of Onion Creek Ranch and Pat Cotten of Bending Tree Ranch. In all cases, it is your responsibility to obtain veterinary services and advice before using any of the information provided in these articles. Neither Suzanne Gasparotto nor Pat Cotten are veterinarians. None of the contributors to this website will be held responsible for the use of any information contained herein.


Goat Camp™ 2023

Taking reservations for
22nd annual Goat Camp™
Oct 23-26, 2023
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Oct 23 - 26, 2023

FAMACHA training.
Doing microscopic fecal counts. Reading fecals.
Learn how to diagnose and treat illnesses and diseases
Nutrition: learn how to feed properly.
Tubing, injections, tattooing, eartagging, handling and restraints.
Hoof trimming, hoof care.
Necropsy demonstration
Diseases affecting goats
Drawing blood, disease testing
Selecting goats for breeding, market sales, etc
Marketing your animals
Humane slaughter demonstration
Breeding, Kidding, Kid care
Importance of private property rights to goat owners
and much more, all on a working goat ranch.

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Additional Information or questions: Suzanne Gasparotto - 512-265-2090 (Texas) or email her at onioncreek@tennesseemeatgoats.com. Quicker response if you do NOT contact through website or Facebook.

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