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Guttural pouches, brain temperature and exercise in horses
Graham Mitchell1, Andrea Fuller, Shane K Maloney
1School of Physiology, University of the Witwatersrand Medical School, 7 York Road, Parktown 2193, Johannesburg, South Africa. mitchg@uwyo.edu
Biology Letters
|December 7, 2006
Summary
Horses do not use selective brain cooling (SBC) to protect their brains during exercise. Their guttural pouches do not function as heat exchangers like the carotid rete found in other mammals.
Area of Science:
- Comparative physiology
- Thermoregulation in mammals
Background:
- Selective brain cooling (SBC) lowers brain temperature below arterial blood temperature.
- Artiodactyls use a carotid rete for heat exchange to protect the brain, especially during exercise.
- Perissodactyls, like horses, lack a carotid rete, prompting theories about guttural pouches serving a similar function.
Purpose of the Study:
- To investigate if horses utilize selective brain cooling (SBC).
- To determine if guttural pouches act as surrogate carotid retes for brain heat exchange in horses.
Main Methods:
- Simultaneous measurement of brain and carotid artery temperatures in free-living horses.
- Monitoring thermal changes during exercise.
Main Results:
- Brain temperature increased by approximately 2.5°C during exercise in horses.
- Brain temperature consistently exceeded carotid artery temperature by 0.2-0.5°C.
- Evidence of cranial cooling was observed, but SBC did not occur.
Conclusions:
- Cerebral blood flow removes heat from the horse brain via convection.
- Guttural pouches do not function as surrogate carotid retes for selective brain cooling in horses.
- Horses do not employ SBC to protect brain tissue from heat injury during exercise.
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