Abstract

To investigate individual differences in thermal status of sheep during voluntary shading, a method of recording body temperatures was developed using data loggers attached to free-ranging animals. During summer, recordings were made of body temperatures of Merino wethers grazing irrigated pasture. Despite shade being readily accessible, the sheep voluntarily stayed in the sun throughout the day. Twenty, 24-h records of intra-abdominal temperature and 12 of concurrent skin temperature were obtained. Both core and skin temperatures exhibited diurnal rhythms influenced by ambient conditions. Short-term fluctuations without obvious cause also occurred in both body temperatures. Skin temperatures of the dorsal surface were considerably higher than previously reported. Core temperatures of sheep voluntarily staying in the sun were not hyperthermic. The maximum 24-h range in intra-abdominal temperature (i.e. 1.9¦C) does not support previous data (Bligh and Harthoorn 1965) that indicated sheep might be more thermostable than other mammalian species. The effective heat load and thermal displacement were apparently insufficient to cause the sheep to seek shade in competition with other factors influencing their behaviour.