Metabolism, respiratory changes, and water balance of an antelope, the eland.

TAYLOR, c. R. Metabolism, respiratory changes, and water balance of ~12 antelope, the eland. Am. J, Physiol. 217(l) : 3 17-320. 1969. The eland is a large East African antelope which can survive prolonged droughts in hot semideserts without drinking. This ability is partly due to a low respiratory water loss relative to the oxygen consumption at night. Each night the eland has a low body temperature, and as its temperature falls, its respiratory rate decreases while the amount of oxygen extracted from the inspired air increases. For a given rate of oxygen consumption, therefore, the volume of expired air and the amount of water lost through respiratory evaporation decreases. Most of the increased oxygen extraction can be expIained by the fact that tidal volume is greater at the lower respiratory rates, and the dead space therefore makes up a smaller proportion of the tidal volume. The eland is so poorly insulated that it must frequently increase its oxygen consumption at night to keep warm. In experiments at 14 C, a temperature often encountered at night, the oxygen consumption of the eland was 19% higher than at 22 C. Ventilation volume, however, was unchanged. Furthermore, respiratory evaporation was less, since body temperature and therefore the amount of water contained in the saturated expired air decreased. The African zebu steer also increased its oxygen consumption at 14 C (by 28%), but its body temperature was more constant and ventilation volume and respiratory water loss increased. low respiratory rate and larger passages of the eland are not favorable to the operation of this mechanism. Thus, McLean (6) has shown that cattle expire air saturated with water vapor at body temperature and one would expect the eland to be similar to cattle. The second possibility, an increased oxygen extraction from the respiratory air, has been found by Joyce and Blaxter (4) in sheep in the cold. 1 was interested in the possibility of the eland increasing the oxygen extraction from inspired air in colder environments and in possible explanations of how this takes place. For a comparison with the eland I selected local zebu cattle. These cattle are herded in the same hot dry areas which the eland inhabits. They are also thinly furred and increase their metabolism to a similar degree as the eland in order to keep warm at night. However, they will not survive droughts without watering. They are therefore particularly well suited for clarification of the physiological mechanisms that account for the differences in drought resistance.