Central and peripheral temperatures and EEG changes during behavioural thermoregulation in pigs

Abstract

Pigs aged about 8 weeks will learn to operate infra-red heaters at ambient temperatures of 20 degree Celsius but not at 25 degree Celsius. Hypothalamic temperature, cortical EEG and skin temperatures have been recorded in pigs exposed to ambient temperatures of 0, +10 or +20 degree Celsius in both heat reinforcement and heat escape situations. The amount of heating received decreased with increasing ambient temperature but at any given ambient temperature there was no significant difference between the duration of heating obtained in the heat reinforcement or heat escape situations. At O degree Celsius, in both situations, the pigs tended to maintain the temperature of their skin which was nearest the heaters at higher levels than they did at +10 degree Celsius. Skin temperatures rarely exceeded 45 degree Celsius. The temperature of the preoptic region was variable but did not change systematically with respect to the behaviour. Observation of the pigs and cortical EEG revealed that during periods of infra-red heating the pigs often became drowsy, but "post reinforcement synchrony" was not seen in the EEG. Cooling the preoptic region by means of an implanted thermode increased the duration of heating in a heat reinforcement situation at 0 degree Celsius and resulted in skin temperatures reaching levels of 45-47 degree Celsius.