Mammals and Birds Regulate the Input and Output of Heat to Maintain Body TemperatureWithin a Narrow Limit
It is customary to measure body temperature as a first part of the clinical examination of mammals. This is because body temperature is maintained within fairly narrow limits despite large variations in ambient conditions.
In diseased animals the ability to regulate temperature can be impaired, for example, by dehydration. In addition, infectious and other agents produce pyrogens that can cause an increase in body temperature. Table 53-2 lists the normal ranges of rectal temperatures in some common domestic mammals. The rectal temperature is somewhat lower than the core temperature of the animal, and changes in rectal temperature lag behind changes in coreTable 53-2
Rectal Temperature (in oC) of Domestic Mammals
| Species | Average | Range |
| Cat | 38.6 | 38.1-39.2 |
| Cattle (beef) | 38.3 | 36.7-39.1 |
| Cattle (dairy) | 38.6 | 38.0-39.3 |
| Dog | 38.9 | 37.9-39.9 |
| Donkey | 37.4 | 36.4-38.4 |
| Goat | 39.1 | 38.5-39.7 |
| Horse | 37.7 | 37.2-38.2 |
| Pig | 39.2 | 38.7-39.8 |
| Sheep | 39.1 | 38.5-39.9 |
temperature. However, rectal temperature is a convenient measure in domestic mammals and provides a useful indication of core temperature.
In well-hydrated animals living in temperate climates, the range of normal temperature is quite narrow. Mammals living in hot, arid climates tolerate a wider range of temperature, allowing body temperature to decrease during the cool nights so that more heat can be absorbed during the ensuing hot day.
To maintain temperature within narrow limits, the animal must regulate its heat inputs and outputs. The inputs and outputs clearly cannot be equal at all times. During exercise, for example, heat production exceeds heat loss. Heat is stored in the body and then dissipates when exercise ceases. The specific heat of body tissues is similar to that of water; therefore, large amounts of heat can be stored without a potentially lethal increase in temperature.