Estimates of the contribution of solar radiation to the thermal exchanges of sheep at a latitude of 55° north

Abstract

Interest in the gain of heat by farm animals exposed to sunshine has largely been confined to countries in which air temperatures are high and in which exposure of stock to sunshine leads to their distress. Riemerschmidt's (1943) studies indicated the considerable magnitude of the heat gained by oxen standing in the sun in South Africa, and studies by MacFarlane, Morris & Howard (1956) in Australia showed that with sheep standing in the sun the wool surface temperature could rise to 85° C. These studies of MacFarlane have been confirmed in Egypt by Eyal (1963), and were subject to a theoretical analysis by Priestley (1957). Such observations, together with earlier ones reviewed by Findlay (1958), show that in many equatorial regions solar radiation is a major factor accounting for heat stress in farm ruminants.