Variations in behavioral thermoregulation in the young pig over 24 hour periods

Young pigs were trained to make a response to obtain a reinforcement of radiant heat. The animals were kept by themselves in a temperature-controlled light-proof room. Some pigs were kept in constant light, some were subjected to a light/dark cycle, and some were first fed ad lib and then deprived of food. The results were analysed by fitting a cosine curve using regression methods and evidence of a circadian rhythm was obtained under all conditions and at ambient temperature between 5 degrees and 20 degrees centrigrade. Most pigs had a peak demand for heat during the true daytime, but in two pigs the peak occurred at night.