If we would like to keep up with the Jones' down the road, we need to keep up with the Johne's in our beef herds. While Johne's disease was first recognized in dairy cows, it is increasingly more common to find it in beef cows as well. It is estimated that at least 8 percent of beef herds across the country are infected with Johne's disease. We are going to cover the biology of the disease, discuss how it is transmitted, address limitations in the testing and cover the Minnesota Board of Animal Health's goal in assisting producers to eliminate the disease from the cattle herds of the state.

Johne's disease, or Mycobacterium paratuberculosis, is an infectious bacterial disease that primarily affects cattle, sheep, goats and other wild ruminants. The bacterium grows in the immune cells of an animal and can be shed in the feces and milk. The bacterium also causes the thickening of the intestinal tract, which inhibits the absorption of nutrients. Extreme diarrhea is the result, which causes the animal to waste away even though it is continuing to eat well. Johne's disease is a slow, progressive disease and the diarrhea develops over time, so infected animals can be shedding the organism even though there are no clinical signs, which is what makes the disease hard to detect. Clinical signs develop a minimum of two years after infection.

Many animals are infected as calves, when their immune systems are not fully functional. Pregnant cows in the late stages of the disease can infect their fetus; studies have shown that 8 to 40 percent of fetuses are infected if their dam is in the late stages of the disease. More commonly, calves are infected by the feces of their dam, or other cows calving in the same pen. Milk from infected dams also contains the bacteria and calves can become infected from the milk or from feces on the teats. A less likely source, but perhaps more of an issue for many beef producers, is pond water. The bacteria can survive in water, though sunlight and heat will kill it. The most common way to bring the disease into a herd is with purchased replacements. We encourage producers to inquire about the disease status of any herd you are buying replacements from, which is important for all diseases, not just Johne's.

Management practices play a critical role in the control of this disease. The main goal is to keep as much adult fecal matter away from calves. There are five key management practices that we can learn from the dairy industry to help control Johne's disease.

1. keep calving areas as clean and dry as possible
2. minimize the density of cow/calf pairs as much as possible
3. use feeding practices that reduce manure contamination of feed and feeding areas as much as possible
4. provide colostrum from the calf's dam or from another single source that is from a test-negative or healthy low-risk animal
5. raise weaned replacements separate from older animals

The limitations in testing for Johne's disease is the major stumbling block to eliminating the disease. Because the disease is such a slow progressing disease, the animal must reach a certain advanced stage in the disease for it to be detected. Current methods will detect less than half of infected animals at one point in time, therefore repeat testing is necessary. There are two main types of tests used: the blood test which is an ELISA test or the fecal test which is a bacteria test. The blood test measures antibodies that are formed in response to the disease, but they are not formed until late stages of the disease. Studies have shown that on average the blood test has a sensitivity of 45% across cows that have some level of shedding. The fecal test will detect about 40% of all infected animals. There are two types of fecal tests, the Polymerase Chain Reaction (PCR) test and the fecal culture. The main disadvantage of the culture is the length of time required to get the test results back. Since M. paratuberculosis is such a slow-growing bacterium, it can take 12 to 16 weeks for results to be known. The PCR is a DNA test and can be completed in about 10 days. Most states require a positive fecal test to officially label an animal as Johne's positive. You can see by the limitations in testing why it is necessary to continuously test animals and also why it is difficult to say an animal absolutely does not have Johne's. You can only say the more tests that result in a negative result, the more likely that animal does not have the disease.

To make things even more difficult, treatment is not an economically viable option and vaccination strategies are very limited in their efficacy. While treatment with antibiotics is possible, milk or meat is not eligible for sale due to drug residue and animals will likely have to be treated for the remainder of its life. Vaccines have been developed but they do not provide a satisfactory level of resistance. The vaccine decreases the development of clinical disease, decreases the amount of shedding and can decrease the economic loss from culling. It does not, however, eliminate or prevent infection of the animal. While a good vaccine would help the battle of Johne's disease, much research needs to be conducted to make this a reality.

Many states, including Minnesota, have recognized the importance of eliminating this disease from cattle herds. The Minnesota Board of Animal Health offers free Risk Assessments which are on-farm consultations regarding Johne's disease. These assessments are performed by either a state/federal district veterinarian or a trained veterinarian in private practice. According to the Minnesota Board of Animal Health, the goal of this program is to identify a producer's highest risks for spreading disease. The veterinarian works with the producer to develop a herd plan which informs producers of what they can do to stop the spread of Johne's disease. These plans are farm specific and due to a producer's input they are also realistic. The state of Minnesota pays for some testing as well to help you identify infected animals. For more information about this program contact the Minnesota Board of Animal Health at 651-201-6824. Many states have similar programs and their animal disease agency can be contacted as well.

While the economic impact of Johne's disease in beef herds is hard to nail down, there is no doubt that decreased reproductive efficiency and increased replacement costs will make any operation less efficient. When using risk assessments, testing, and management changes, Johne's disease is manageable and reducing or eliminating the disease from your herd will benefit the cattle industry.