Johne’s Disease: A Silent Threat to Beef Cattle

Diarrhea. Nobody wants to experience it, and nobody wants to talk about it. However, chronic diarrhea is a common symptom in ruminant animals that are infected with the bacteria known as Mycobacterium avium paratuberculosis (MAP), more commonly known as Johne’s Disease.

Johne’s Disease is very well known and diagnosed in the dairy world. In 2008 the “National Animal Health Monitoring Survey on Johne’s” study estimated about 68% of U.S. dairy herds have at least one cow test positive for Johne’s. In the beef world, Johne’s disease is a silent threat. The same study as above estimated that 8% of the U.S. beef herds also contain at least one positive testing cow. Although Johne’s Disease seems less widely distributed in beef herds, it is still a critical issue to all beef producers.

Clinical Signs and Stages
Calves are exposed to Johne’s bacteria (MAP) at a young age. This typically happens shortly after birth when they come in contact with MAP bacteria in feces, across the placenta to unborn calves, contaminated soil/water, milk from infected cows, and contaminated teats. Calves will not develop clinical signs until two or more years after the initial exposure of the MAP bacteria. Adult livestock (2 years +) are very unlikely to contract Johne’s disease if they were never exposed to the MAP bacteria prior to 2 years of age.

There are four stages to Johne’s Disease:
Stage I: Silent, nondetectable infection.
• Typically occurs in calves and young stock under two years of age. Current tests cannot detect infection in animals two years of age or under. Some animals may recover at this stage; others will progress to stage II slowly, over many months to years.

Stage II: Subclinical Shedders.
• Typically occurs in heifers or older animals. Animals appear healthy but shed the MAP bacteria in their manure at levels high enough to be detected by tests.

Stage III: Clinical Johne’s Disease.
• The MAP bacteria invade the intestine, causing the following clinical signs typically brought on by stress: intermittent diarrhea, weight loss, and abnormal appetite. These animals are high shedders of MAP bacteria in their manure– fecal and blood tests will be useful. Clinical signs may last days to weeks and then progress to stage IV.

Stage IV: Emaciated animals with fluid diarrhea.
• Terminal stage of the disease. Animals are extremely thin and may develop swelling under the jaw, which is referred to as “bottle jaw.” Most animals will continue to deteriorate quickly at this stage since there is no treatment for Johne’s Disease.

How to Prevent/Control Johne’s
Prevention is the most cost-effective way to manage Johne’s Disease. Any beef herd that is not closed (has ever purchased cattle) should be considered at risk for having Johne’s Disease. When buying replacement animals, producers should inquire about Johne’s status in that herd before buying the animals. Ask if the herd has been tested for Johne’s Disease for several years and has been certified free of the Disease. Buying from reputable producers that know the level of Johne’s in their herd will help to reduce the spread of Johne’s into your herd. For commercial producers that retain replacement heifers, have no previous history of Johne’s Disease in their closed herd, and are only purchasing bulls, yearly testing of purchased bulls (2 years or older) before turnout may aid in decreasing the risk of disease.

There are two main diagnostic tests available for Johne’s testing: fecal PCR and blood ELISA. The blood test (ELISA) should be utilized in the early stages of the disease (prior to showing clinical signs) and is used for herdwide screening for Johne’s. The fecal test (PCR) is a more accurate test for animals that are in the later stages of the disease and showing clinical signs. The fecal tests should not be used in the early stages of the disease when animals are potentially not shedding the MAP bacteria in their feces. *The Johne’s timeline above gives a good depiction of how and when fecal shedding of the MAP bacteria occurs on and off and especially during stressful periods of a cow’s life (calving, breeding, etc.). Other prevention strategies include reducing manure buildup in areas where animals congregate and keeping calving areas as clean as possible with frequent new bedding to reduce the exposure of newborn calves to adult manure (MAP bacteria). Producers are also advised to sell replacement heifer calves that are offspring of any Johne’s test-positive cows.

Contact your local Sioux Nation Ag Center veterinarian if you have any questions about Johne’s or suspect you may have Johne’s in your herd.