Heat and water in tropical Merino sheep

Abstract

The relation between environment and the water intake and output of young Merino sheep living in the hot dry tropics on lat. 21° S. has been studied for 3 years. The tip wool of sheep standing in the sun heats to 189°F by absorption of radiant energy, most of which is re-radiated. Wool, especially when it is more than 3 cm long, assists in protecting sheep from radiant energy. The respiratory rates of sheep shorn during summer were more than twice those of unshorn sheep standing in the sun. On the open plains summer shearing appears to add to the thermal strain. Acclimatizing sheep respired more rapidly in the sun than tropical sheep. Evaporative cooling, by panting, increases water demand, and in summer merinos drank on the average 12 times as much water as in winter, when they took 7.3 ml/kg/day. Water intake is related closely to respiratory rate. Urine output was lower in summer than in winter.