| Camel milk. Properties and Products |
The habitat of the camel is characterised by large variations in temperature and scarce irregular rainfall. In the course of evolution, the camel adapted in various ways to the conditions of that environment. In the following, some of the particular mechanisms of the adaptation of the camel are briefly described. For more comprehensive information, the reviews of Schmidt-Nielson (1964) and Yagil (1985) are recommended.
The hump contains fat and metabolism of fat yields an amount of water greater than the weight of the fat. Since oxidation requires oxygen the necessary ventilation of the lungs involves a loss of water vapour. This loss exceeds the amount of water formed.
The body temperature of the camel is quite variable, and when the camel is deprived of water the daily fluctuations may exceed 6° C. These fluctuations are important in the water balance for two reasons: Firstly, as body temperature rises during the hot day, water otherwise used to keep the temperature down remains unexpended. The excess heat is stored in the body and is dissipated to the cool environment at night without use of water. Secondly, an elevated body temperature reduces the heat flow from the hot environment to the body, and, therefore, reduces the amount of water needed to prevent further temperature rise.
The camel can withstand considerable dehydration. In a hot environment it can tolerate a loss of at least 27 % of the body weight, twice the dehydration that brings other mammals into lethal explosive heat rise. The limit for dehydration of the camel is unknown. When the camel becomes dehydrated the loss of water is not accompanied by a proportional loss in plasma volume. The maintenance of a high plasma volume facilitates circulation, which is one of the first functions to suffer during dehydration of other animals in hot environments.
In a hot environment the fur is an important barrier against heat gain from the environment. When animals with and without fur are compared under otherwise identical conditions it is found that less water is used by unshorn camels. The camel does not pant, but does sweat. Sweat is produced in moderate quantities, but the fur is not wetted and appears dry. Water evaporates from the surface of the skin rather than from the surface of the fur, an important factor in water economy.
The camel has powerful kidneys which can produce a concentrated urine. Adequate studies of the concentrating ability of the kidney are lacking. Under certain circumstances urea can be withheld from excretion and be resynthesized into protein by the microbial flora of the rumen (Schmidt-Nielson et al. 1956b; Macfarlane 1968).