Seasonal variations in wool growth and heat tolerance of sheep. II. Heat tolerance

Abstract

The heat tolerance of rams at an air temperature of 105°F (40.6°C) and 34 mm Hg water vapour pressure was studied over a period of 1 year at Beltsville, Maryland. The rams were more heat tolerant in summer than in winter. This difference was significant (P < 0.001). Tolerance was less in July than in June and August. The reasons for this are discussed. Shearing increased the heat tolerance of rams (P < 0.001), presumably by enhancing the efficiency of evaporative cooling from the skin. There is evidence that shearing reduced heat acclimatization, especially during the cooler months.