Temperature and humidity

Mammals and birds are homeotherms which means they need to maintain a constant core body temperature.

If core body temperature falls the animals become hypothermic. A fall of 7-8°C is undesirable but can often be followed by complete recovery.

If core body temperature rises the animals become hyperthermic. An increase of only 5°C, in many cases, will be fatal.

Animals are constantly producing heat from their metabolism. They must balance this heat production with heat loss in order to maintain a constant body temperature.

Total heat produced by the animal = Total heat lost by the animal

Heat is lost to the environment by several routes: convection, radiation, conduction and evaporation.

Loss of heat by convection, radiation and conduction is ‘dry’ and depends on there being a temperature gradient between an animal and its surroundings, e.g. when lying on a cold concrete floor there will be conduction of heat from the animal to the floor.

Loss of heat by evaporation is ‘wet’ and depends on there being a gradient of water vapour between an animal and its environment, e.g. when the atmosphere is hot and humid, the effectiveness of sweating or panting to cool down is reduced.

A combination of high temperature and high humidity can cause severe heat stress to animals within a livestock vehicle.

As animals are continually producing heat, the risk of heat stress is much greater than that of cold stress, particularly when the vehicle is fully loaded.

Animals conserve body heat or increase their body temperature by:

• shivering;
• piloerection (raising of the hair/coat);
• huddling;
• postural changes.

Animals are less likely to suffer cold stress in transit. The risk of cold stress is increased with cold environmental conditions, very young or shorn animals, or by having very few animals on the vehicle.

Next: Vehicle Ventilation