The highest ambient temperature tolerated by normocapnic and hypercapnic rabbits

Area of Science:

• Physiology
• Animal Science
• Environmental Health

Background:

• Understanding animal thermoregulation is crucial for welfare and research.
• Rabbits exhibit unique physiological responses to heat stress.
• Limited data exists on rabbit thermoregulatory limits under high humidity.

Purpose of the Study:

• To determine the highest ambient temperature rabbits tolerate at high relative humidity.
• To investigate rabbit thermoregulatory mechanisms, including vasomotor and respiratory responses, under heat stress.
• To assess the impact of elevated carbon dioxide on thermoregulation in heat-stressed rabbits.

Main Methods:

• Rabbits were exposed to ambient temperatures of 30°C with 80-95% relative humidity.
• Vasomotor and respiratory responses were monitored.
• Carbon dioxide (3, 6, 9%) was introduced into the inspired air mixture.
• Exposure duration was approximately 4 hours for prolonged heat stress assessment.

Main Results:

• The highest tolerated temperature was 30°C at 80-95% relative humidity.
• Vasomotor thermoregulation was fully activated, but thermal panting capacity was not reached.
• Prolonged heat exposure led to a decrease in respiratory frequency.
• Elevated carbon dioxide concentrations (3-9%) did not disrupt thermoregulatory mechanisms.

Conclusions:

• Rabbits can tolerate 30°C at high humidity, with vasomotor responses compensating for heat.
• Respiratory panting is not fully utilized at these limits, and prolonged exposure can be suppressive.
• Thermoregulation in rabbits is robust against moderate increases in carbon dioxide under heat stress.