Thermal status of sheep at pasture in western New South Wales

Abstract

The thermal status of three unrestrained rams at pasture was studied for a period of 5 days during March in central western New South Wales. A temperature telemetry system was used to measure rectal temperatures, skin surface and subcutaneous temperatures on the mid back, and subcutaneous temperatures of the scrotum of each ram. Rectal temperatures of 40¦C and above were recorded for all rams on each day, the highest recorded being 41 9 4 and 41.6¦. Rectal temperatures in excess of 40¦ were also recorded for extended periods between 6.00 p.m. and midnight. Although respiratory frequencies increased with the increase in environmental heat load during the day, no obvious signs of extreme heat stress were noted at these elevated rectal temperatures, whereas sheep exposed to high heat loads in indoor experiments consistently exhibit heat stress at similar rectal temperatures. Rectal temperatures were generally higher and more variable than those reported by other workers for penned sheep in either indoor or outdoor environments. Subcutaneous scrota1 temperatures were usually lower than those which might be expected to induce sterility. Variations in the temperatures measured have been related to the thermal environment and patterns of behaviour of the sheep.