Environmental aspects of pneumonia control in calf units on British dairy farms

Abstract

Calf pneumonia is a major cause of disease and mortality in British cattle rearing units and the aerial route is a major method of transmission of infection between calves. Central to adequate ventilation is the provision of fresh air at the correct height for the cattle. In the case of young calves, air flows may need to be limited to prevent the air temperature inside the shed falling below the animal's lower critical temperature. Where high enough temperatures cannot be maintained, then techniques, such as encouraging ‘nesting’, providing ‘calf jackets’ and raised planes of nutrition, can be used. The airborne survival of the common pneumonia pathogens is lowest at mid-range humidities (40–60% relative humidity), but in the winter the humidity in calf sheds rarely falls this low. The commonest form of ventilation in cattle sheds is natural ventilation with the stack effect and cross drafts responsible for bringing fresh air into the shed. In many youngstock builds there is insufficient heat production to drive the stack effect and cross drafts will vary with the external wind direction and speed and will be reduced by the ‘wind shadow’ of neighbouring buildings. Forced ventilation systems can be used; negative pressure systems require careful build design, construction, maintenance and use and are most commonly suited to new builds. Positive pressure systems can work better in existing building stock but need careful design, building and installation and cannot be altered to accommodate seasonal variation.