• Feeding colostrum to calves by bucket, and thereafter feeding only milk replacer or pasteurized milk

  • Preventing contamination of calf feedstuffs, water, or bedding by effluent from the adult herd

  • Applying manure from the adult herd only to cropland or to pastures grazed by adult stock

Few empirical studies of those control program components have been done, and their justification is based on biologic plausibility, limited observation, and anecdotal evidence.

Implementation of herd or flock level control programs, establishment of test-negative or low-risk herds and flocks, and reduction of environment and food contamination with Map are attainable current goals. The possibility of eradication of JD in the United States should be evaluated after significant progress in control programs is attained.

Environmental Factors in Infection Control Practices

In most, if not all, affected species, Map is believed to be transmitted primarily in a fecal-oral cycle shed in the feces of infected animals and then ingested by susceptible animals. Such a cycle is also the primary means by which most other communicable enteric infectious agents are transmitted. For Map transmission by indirect contact, factors include the number of organisms shed in the feces and the organism’s survival characteristics in the environment. The relationship between Map and the environment is complex, involving factors such as the physical characteristics of the substrate material (feces, water, milk, manure slurry, dust, environmental surface, dirt), temperature, pH, water activity or content, and competing microorganisms. The relationships are not well defined for the many combinations encountered in the farm environment, but decisions must still be made for control programs. More importantly, current information relates to the duration of environmental survival of a large inoculation of laboratory-origin Map, which could respond differently from Map originating directly from an infected host (Mitscherlich and Marth, 1984). More information on the environmental survival characteristics of Map is needed to determine how long the organism remains infectious once the area or material (water, grass, forage, or other feedstuff) becomes contaminated, leading to an estimate of dose and response over time. All of this is critical information for determining how to manage livestock flow through housing facilities or paddocks and for how to otherwise minimize disease transmission. Some recommendations do not provide risk estimates of cost relative to benefit. For example, there is a recommendation that livestock producers keep young animals from grazing pasture that has been fertilized with Map-contaminated manure for at least one year after birth. But because producers could regard that practice as infeasible and the risk relatively insignificant, they choose to ignore it. In fact, these recommendations may well



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