|
110. The objective of ventilation is to provide a supply of draught-free fresh air and to remove pathogenic micro-organisms, moisture, dust and gaseous waste from within the livestock building. If ventilation is not satisfactory, there is an increased likelihood of mastitis and the spread of respiratory disease causing loss of production and, in some cases, death. Good ventilation is therefore vital for the health and welfare of dairy stock.
111. Most cattle houses rely on natural ventilation achieved on a still day by the upward movement of warm air within the building. This results from the heat generated by the stock which causes the internal temperature to rise above that of the outside air. As the warm air escapes at the highest point, colder air from outside is drawn in. This effect can be lost in wide or lofty buildings or where buildings are understocked.
112. The outlet of a building is the most influential factor controlling natural ventilation and should be located at the apex where a continuous open ridge (which may be protected) is formed. The inlet is normally located below the eaves but above the height of animals housed to prevent draughts. The inlet may be a continuous gap but is more normally provided by space boarding, netting or similar to control entry of rain or snow.
113. In certain circumstances, such as multiple span buildings, it is not possible to provide sufficient air inlet. In such cases, the provision of slotted roofs or raising the end of each roof sheet may help to provide the necessary ventilation. It may be appropriate to vary the height of eaves on new, multi-span buildings in order to provide more inlet ventilation.
114. All new buildings should be designed by a competent person who is well versed in animal welfare requirements. The buildings should provide adequate ventilation (throughout the year) for the type, size and number of stock to be housed.
115. Where ventilation in existing buildings is inadequate, buildings should be modified by improving inlets and/or outlets and, if necessary, by making more radical changes to air movements, such as cutting slots in the roof.