Studies on the adaptability of three breeds of sheep to a tropical environment modified by altitude IV. Role of the fleece in thermoregulation in German Merino ewes

Abstract

The influence of fleece on thermoregulation in German Merino ewes was investigated in Rhodesia. Comparative heat tolerances of Persian Blackhead, indigenous Native and shorn and unshorn Merino ewes were obtained during the hottest month of the year in Northern Rhodesia. The main thermolytic responses in unshorn, partially shorn and completely shorn Merino ewes were measured at 7.0 a.m.; 10.0 a.m.; 1.0 p.m. and 4.0 p.m. during April in Southern Rhodesia.1. Unshorn Merino ewes showed more and shorn Merino ewes less effective body temperature regulation than Persian or Native ewes. High heat tolerance in unshorn Merinos was due primarily to insulation by the fleece and not to more efficient physiological thermolysis than in hair breeds. No ewe showed signs of undue thermal stress and feed intake was not affected by heat.2. Increases in rectal temperature and respiratory rate between 7.0 a.m. and 1.0 p.m. of Merinos in Southern Rhodesia were related inversely to fleece length. Body temperature did not differ significantly at 1.0 p.m. owing to differential rates of increase in respiratory rate.3. Magnitude of the diurnal fluctuation in skin temperature was also related inversely to fleece length. Partially shorn ewes, however, began with and maintained highest skin temperature through the heat of the day. In all groups skin temperature fell after 10.0 a.m. although ambient temperature continued to rise. This fall could not be attributed to sweating since moisture secretion declined simultaneously.