Whilst it is important to identify the infectious agents in outbreaks of enzootic pneumonia on a farm basis in order to target prevention and control of this disease complex, there are some common approaches to husbandry and management that are likely to reduce the incidence of enzootic pneumonia, independent of the causative factors. These approaches can be divided into three areas:

1. Maintenance of disease resistance;
2. Reduction of stress; and
3. Reduction of exposure.

 Maintenance of disease resistance

In order to provide the calf with a passive immune protection before its own immune system is fully functional, the calf needs to receive adequate amounts of colostrum containing a sufficient quantity of immunoglobulins. An amount of 3-4 litres of colostrum that contains 50-150 g/litre of immunoglobulin IgG within the first 24 hours of life has been recommended (Besser et al., 1991).

As many calves fail to ingest adequate amounts of colostrum without assistance, studies show that bottle feeding of colostrum provides higher levels of immunoglobulins in the serum of the calf than allowing calves to suckle on their own (Besser et al., 1991). On the other hand, it has been shown that calves that are allowed to suckle the dam have an increased rate of absorption of immunoglobulins from the gut (Edwards et al., 1982).

First and second parity cows have significantly lower levels of immunoglobulins in their colostrum than higher parity cows. It has also been shown that cows that a dry period of less than four weeks produce colostrum with low immunoglobulin levels (Logan et al., 1981). It has been shown that a large proportion of dairy calves acquire inadequate amounts of colostrum after calving, leading to both inadequate ingestion of colostrum and inadequate absorption of immunoglobulins (Petrie, 1984).

Whilst the transfer of maternal immunity is important, it does not protect the calf well against respiratory pathogens after two to three months of age, when the concentration of maternal serum antibodies is low and the calf’s own immune system is still not fully functional. (Corbeil et al., 1984) The highest incidence of respiratory disease occurs in many herds during this period, and prevention should concentrate on reducing stress at this time (see below).

A further factor limiting immune protection against respiratory diseases is that some of the pathogens are immunosuppressive (Woldehiwet and Sharma, 1992). Both Mycoplasma bovis and bovine respiratory syncytial virus belong to this category and, when endemic in a herd, can reduce the calves’ ability to resist disease. Eradication of M. bovis from a dairy herd has been shown to improve calf health (Byrne et al., 1998).

Vaccines are widely used to boost the calf’s immunity against many respiratory pathogens. Vaccines are available in the UK for respiratory syncytial virus, parainfluenza 3 virus and infectious bovine rhinotracheitis virus. There is also a combination vaccine against the last two viruses. The vaccines should be used as a part of a disease prevention programme that also addresses the environmental and management factors on the farm. Vaccines can also be used to eradicate some respiratory diseases in problem herds (Pospisil et al., 1996). However, the efficacy of the vaccines varies significantly between farms, and it is difficult to establish control programmes that work continuously (Donkersgoed et al., 1990; Straub and Mawhinney, 1988; Howard et al., 1987). The vaccines can also be used successfully in the face of an outbreak once the first affected animals have been diagnosed and the agent identified.

Prophylactic use of antibiotics has also been successful in calf rearing units, with antibiotics being administered to all arriving animals. This practice is, however, banned under the organic standards.

Reduction of stress

Gradual weaning, timing of disbudding and castration not to coincide with weaning, minimisation of transport, avoidance of cattle markets and avoidance of cold stress have all been recommended as ways to reduce stress in young calves. Respiratory diseases often follow a pattern in a herd. Recording disease incidences and treatments can be helpful in establishing whether such a pattern exists. If a pattern is identified, potential stressful events around disease peaks can be recognised and management practices changed to reduce stress.

Overcrowding, poor ventilation and high humidity all cause respiratory stress in calves and make them more susceptible to respiratory disease. Reasonable space allowance and good ventilation will reduce this stress and make pneumonia less likely.

Reduction of exposure to infection

Close contact with other animals allows respiratory disease agents to spread easily. Individual hutches can reduce respiratory disease in comparison with group-housed calves, and limiting the number of animals in the same air space can limit the spread of existing infection (Ostergaard et al., 1986). Similarly, keeping age groups separate and group sizes small has been shown to reduce respiratory disease.