During live shipment, sheep can be exposed to prolonged periods of high heat and humidity, while environmental conditions in a Western Australian sheep feedlot have not yet been assessed. The research described in this thesis was conducted to determine the physiological responses of sheep to conditions within the live export and feedlotting industries, with particular focus on that of heat stress. This work also developed methods to determine the critical wet bulb temperature, otherwise known as the heat stress threshold (HST) of Merino rams, ram lambs and wethers exposed to live export...