All the species of ruminants investigated were observed to decrease
their intake of food when they were dehydrated in an environment
of 22 °C. The domestic species (Turkana goat, fat-tailed sheep
and Zebu cattle) showed the greatest reduction in food intake (average
—53%, Table 4). When the effects of heat load were added to that of
dehydration, the two species of non-domestic, arid-adapted ruminants,
the Grant's gazelle and the Oryx showed no further reduction in
food intake. The Oryx even displayed an increase in its food intake.
Those species classified as non-domestic, non-arid adapted (Thomson's
gazelle and Wildebeest) and the domestic, arid-adapted species
(Turkana goat, fat-tailed sheep and Zebu cattle) showed a further
reduction in food intake when dehydrated and exposed to intermittent heat load for 12 h at 40 °C. At least a part of the decrease
in food intake of a dehydrated animal reflects a decrease in
metabolism (Payne and Hutchison, 1963; Taylor, 1974). This lower
metabolic rate could be considered an adaptation for the conservation
of water, since the animal generates less heat, which has to be
dissipated through evaporation at high environmental temperatures.
A low metabolic rate also decreases the maintenance requirement
when food is in short supply (Taylor, 1974; Choshniak et al. (1995).
Studies of Taylor (1974) on Zebu cattle, Merkt and Taylor (1989;
1994) on desert rats, Kamau and Maloiy (1981) on the dik-dik antelope
as well as those of Choshniak et al. (1995) on black Bedouin goats have
clearly shown that desert animals do have a “metabolic switch” or
metabolic adaptation that enables them to survive famines and food
shortages. Further Silanikove (1994) has demonstrated how most
ruminants maintain water and electrolyte balance as well as ionic and
osmoregulation when faced with severe dehydration and dehydration.
Hematocrit values may be used to measure the degree of
dehydration in animals. In the present studies, the measurements of
hematocrit was not used to ascertain the degree and level of
dehydration in our experimental animals. Previous experiments
carried out by Maloiy and Boerer (1971) under similar conditions on
zebu cattle and the domestic donkey did use this parameter to assess
the level and degree of dehydration.