Johne's Disease Is An Increasing Problem - Should Manure Be Applied To Forages?

Application of manure from animals infected with pathogens to crops for animal consumption is a potential method for spreading infection.

Johne's (yo-nees) Disease is a persistent and debilitating bacterial disease that affects the intestines of ruminant animals, including cattle, goats and sheep. The disease is especially problematic in dairy herds, where many cattle can be infected, but only a small percentage of animals (<5%) show the clinical signs of chronic diarrhea and extreme weight loss. These cows also experience decreased milk production. Infected cattle, even those not showing sickness, may shed the bacteria in the manure. Johne's is most often introduced onto farms by the purchase of infected animals.

Animal Susceptibility To Infection

Johne's Disease is caused by Mycobacterium avium paratuberculosis (MAP). Calves, especially those under 6 months of age, are most susceptible to infection. Animals under stress are also more susceptible than healthy cattle. The common routes of infection are via ingestion of colostrum or milk contaminated by infected cows. For this reason, Johne's prevention strategies revolve around calf management and herd testing. (Refer to Healthy Cows for a Healthy Industry at www.johnes.org.) Infection can also occur when feed contaminated with manure containing the MAP pathogen is eaten, particularly by youngstock. . For this reason, manure application to forages is a potential source of infection.

Survival of the Disease Bacteria In the Environment

MAP can survive in manure and water for up to one year and on pastures and hay fields for up to six months. Exposure to sunlight, drying, high pH, liming, and low iron, as well as the processes of fermentation and composting appear to reduce the survival of MAP. Factors that reduce the survival of the bacteria can also help in better managing manure applied to forages to prevent spread of MAP.

Management Strategies

The following Management Strategies are suggested for manure management in herds where Johne's Disease has been identified:

• Manure should not be applied to forages in calf or heifer pastures during the grazing season.
• Topdress the liquid manure as soon as possible following harvest. This allows the sunlight and desiccation to kill the MAP bacteria.
• Apply manure to fields that will be ensiled or harvested for haylage. Proper fermentation appears to kill the bacteria. Use good ensiling techniques, including proper dry matter content, use of silage inoculant if required, rapid filling, adequate packing, and covering as soon as the storage is filled.
• Avoid application of manure to fields that will be harvested for dry hay, especially calf and heifer hay. Where manure is applied, it should be done before any re-growth occurs. A 30 day interval between manure application and harvest should reduce MAP bacteria numbers. However year-to-year variations in environmental conditions (weather) cannot guarantee complete elimination.
• When choosing a field for manure application, those with a high pH or those that have recently had lime applied are preferred.

Management strategies that help to control Johne's Disease will also help to control other common pathogens such as Salmonella, E.coli, Cryptosporidum and several other viral diseases that affect young calves and cattle.

E. D. Thomas - William H. Miner Ag Research Institute