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AABP News |
Critical Management Points for Prevention and Control of Johne's Disease in Beef Cattle Prepared and edited by Don Hansen and Christine Rossiter of the AABP Food Safety Committee and the National Johne’s Working Group
Premise for critical management points 1. Management points directed at prevention or control of Johne’s disease will also reduce the risk for other important cattle pathogens such as rota and corona viruses, E. coli, Salmonella sp., coccidia and Cryptosporidia. They will also help to improve animal performance. 2. Johne's disease is caused by the acid-fast, intracellular bacteria, Mycobacterium avium subspecies paratuberculosis, which infects intestinal track. During the final stage of infection the pathogen is disseminated to other organs as well. The infection causes diarrhea, poor performance, wasting and death. Clinical signs of the disease occur more commonly during the end stages of the infection. 3. Calves are at highest risk for infection and most susceptable. 4. Not all cows advance to clinical disease. What proportion and why is unknown. 5. The infection is chronic and mostly subclinical in nature. Thus, Johne's should be regarded as a herd-wide problem, not just a matter for individual cows that exhibit end-stage clinical signs. 6. An infected cow may shed the pathogen in her feces for months to years before she develops clinical signs. The cow may shed 106 to 108 mycobacteria/gram of her manure, thus severely contaminating her immediate environment. In the final stage, there may be 30 to 30,000 mycobacteria per ounce in her colostrum and milk. The bacteria can disseminate to infect a fetus in utero. 7. Johne's disease can be prevented, controlled and even eliminated from infected herds by applying critical management points that are based on an understanding of the epidemiology and pathogenesis of the disease. 8. Prevention or control of Johne’s takes commitment and time. Half-hearted attempts to prevent or control the disease will generally fail. Prevention is in all ways, cheaper than control. After the infection enters a herd it may be years before clinical signs are noticed and is likely to take five or more years to control. Prevention The NAHMS Beef ’97 survey showed that 80% to 90% of U.S. beef herds were at low risk for, or may not have Johne’s disease. Therefore, prevention should be the goal of every beef cattle operator. There is a need for low-risk and infection-free replacement animals. Veterinarians should encourage their cow/calf producer clients to find out their herd’s Johne’s infection status. If they are Johne’s-free, assist them with plans to prevent entrance of infection. The basics of preventing the introduction of Johne’s disease are straight forward: close the herd to infected replacements, recipients, bulls or herd additions; and guard against entry of manure contaminated equipment, feed, water and contaminated colostrum or milk from other herds. Recall that current tests are adequate tools that function well at the herd level for determining the infection status of the client’s herd, or that of potential replacement animals from tested herds. However, they have low accuracy in detecting the early stages of infection, even in mature animals. Negative test results from immature animals (<24 months of age) for Johne’s generally have limited value. The Johne’s disease-status of a source-herd provides critical information for estimating the infection status of an individual. Confidence that an animal, or herd, is not infected requires repeated tests with negative results, taken over time. However, national, USAHA approved, guidelines exist to establish a low risk herd status using cost effective testing. I. Critical Management Points for Prevention of Johne’s Disease A. Prevent infections by closing the herd to animals with an unknown Johne’s infection status. - The owner uses the critical management points against Johne’s disease. - Test them two or three times at six to twelve month intervals, depending on the level of assurance desired. -Confidence in actual Johne’s disease prevalence will depend on sub-sample size. See the testing protocol for the National Johne’s Herd Status Program for examples of statistical subset sample sizes and their respective confidence limits. 4. Pre- and post-test adult animal additions. - Test them two to three times at six to twelve month intervals for increased confidence in their negative status. Additional steps are required to control infection. The critical management points in beef herds are aimed at protecting young stock from infection and reducing the pathogen load in the environment to reduce risk for transmission to young cattle. Identification and removal of infected animals may be more important in the beef herd because separation of young calves from adults is not practical. Capitalize on the decision to manage against Johne's disease by addressing other health and performance issues on the ranch or farm that involve the same management areas and can be targeted as additional client goals. Examples include reducing risk for
other pathogens, improved calving management, improved heifer development,
reducing feed waste and improving pastures.
II. Critical Management Points for Control of Johne’s Disease A. Reduce infections by manure management (all manure is suspect). - Clean calving area, keep cow density low, avoid overcrowding. - Move new cow/calf pairs to clean pasture as soon as bonding occurs. - Avoid keeping high risk or sick cows
in common calving area.
- Do not allow young stock and infected adults to use the same feed, pasture, or water sources. - Consider forage crops that had fresh manure applied as fertilizer during the current growing season as a feed risk to young stock. - Use separate equipment to handle
manure and feed.
- Use troughs or panels to restrict access to streams and ponds. - Divert manure runoff from water sources.
- Prevent transporting bacteria to young stock by people, runoff and equipment. B. Reduce infections by colostrum management. - Thoroughly clean the udder and teats before collection to avoid fecal contamination. - Consider using quality commercial colostrum supplement products. - Cull test-positives immediately, or segregate them from calving area and young stock. - Consider culling or segregating all
offspring of these infected dams.
- Cull, segregate, or manage them to reduce pathogen exposure to others. - Have a plan for high and low risk animals, based on test results, that enhances control efforts. - Strongly consider keeping replacement animals only from test-negative cows. - Schedule herd-testing to provide
timely information for herd management, i.e., testing at herd pregnancy
examination or herd vaccination time.
- Consider pretesting, including the source herd, where appropriate. - Isolate, observe and test new arrivals
before adding to herd, then integrate them into the routine test program
- Take the time to work with your clients to develop a prevention or control plan that fits their operation. - Assess herd history and estimate the level and potential impact of Johne's disease. - Do a risk assessment of areas where infection can spread on the farm or ranch. - Help clients define specific control measures to meet their objectives and situation. - Make a team involving employees and other advisors, from the start, who will be responsible for carrying out the plan long term. - Review plans and records regularly. Identify and address problems
as they arise.
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