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Warm blooded species of animal maintain their body temperature within a fairly narrow range, although there is some variation depending upon the time of day, degree of exercise and so on . Other species of animal do not have such a sophisticated system for controlling body temperature and reptiles for example are poikilothermic - which means that their body temperature varies with the surrounding environmental temperature. When temperatures are high they increase in activity, when environmental temperatures are low their metabolic rate and activity rate fall as well.

The "normal" body temperature range may vary depending upon the method of measurement used. The most widely used method is to take the temperature using a mercury thermometer inserted into the animal's rectum although other orifices can be used (e.g. the vagina). Recently modern technological developments have lead to the use of electronic monitors which are inserted into the external ear canal.

Method for taking body temperature with a mercury thermometer
The rectum should be clear of faeces, and the mercury must be shaken down to the bulb end of the thermometer before inserting it. The thermometer should be held in place for 2 minutes before reading it.

Species variations

Species Normal Critical point


100.9 - 101.7o F ; 38.3 - 38.7o C

105.0oF ; 41.0 o C


100.4 - 101.6o F ; 38.0 - 38.5o C



99.0 - 103.0o F ; 37.0 - 39.4o C



98.0 - 101.0o F ; 36.2 - 37.5o C


Guinea Pig

99.0 - 103.0o F ; 37.2 - 39.5o C



100.5o F ; 38.0o C

102.0o F ; 38.8o C


101.5o F ; 38.5o C

103.0o F ; 39.4o C


102.5o F ; 39.2o C

104.0o F ; 40.0o C


102.0o F ; 38.8o C

103.5o F ; 39.7o C

  • If the temperature exceeds the critical point for the species hyperthermia exists.
  • Body temperature can vary by as much as 2oF (1oF) in many species during the day.

Last updated : October 2013