The rectal temperature of normal healthy camels at rest may vary from about 34°C to more than 40°C. Diurnal variations in the winter are usually in the order of 2°C. In summer the diurnal variations in the camel deprived of drinking water may exceed 6°C, but in animals with free access to water the variations are similar to those found in the winter. The variations in temperature are of great significance in water conservation in two ways. a) The increase in body temperature means that heat is stored in the body instead of being dissipated by evaporation of water. At night the excess heat can be given off without expenditure of water. b) The high body temperature means that heat gain from the hot environment is reduced because the temperature gradient is reduced. The effect of the increased body temperature on heat gain from the environment has been calculated from data on water expenditure. These calculations show that under the given conditions the variations in body temperature effect a considerable economy of water expenditure. The evaporative heat regulation in the camel seems to rest exclusively on evaporation from the skin surface (sweating), and there is no apparent increase in respiratory rate or panting connected with heat regulation. The evaporation from isolated skin areas increases linearly with increased heat load. The critical temperature at which the increase sets in is around 35°C. The fur of the camel is an efficient barrier against heat gain from the environment. Water expenditure is increased in camels that have been shorn.

No abstract

Camels ( Camelus dromedarius) were exposed to prolonged periods of water deprivation during winter, spring and summer in the Sahara desert. Determinations were made of: weight changes, water and food intake, urine flow and concentrations, plasma concentrations, etc. It was found that the camel can tolerate a loss of water corresponding to 30% of its body weight even when exposed to the severe desert heat. Other mammals dehydrated in a hot environment may die from circulatory failure already when the water loss involves 12% of the body weight. Unlike many other mammals the camel does not lose its appetite when deprived of water but continues to eat normally until the desiccation becomes very severe. It has a low urine output (0.5–1 l/day when kept on a diet of dates and hay), a low water content in the feces, and, when dehydrated in the summer, a very low evaporative water loss. When offered water the camel drinks in 10 minutes enough water for complete rehydration. The longest period that we kept a camel on dry food without drinking water in the hot summer was 17 days. This camel was not working and it had its protective fur which decreased the heat gain from the environment. It is concluded that the ability of the camel to withstand prolonged dehydration is due to: a) tolerance to an extremely high degree of desiccation of the body and b) low overall water expenditure. Particularly effective as a water conserving mechanism is the low evaporative water loss during dehydration in the summer.

Utilization of injected urea and urea transfer from blood to rumen were investigated. First, urea ( ca. 5 mmole urea-N/kg body weight) was injected intravenously into mature sheep receiving a low-protein, carbohydrate-supplemented ration. Part of the injected urea was recovered in urine as excess over basal excretion. 52% (S.D. = 10) of injected urea was not recovered in urine nor remained in body fluids and presumably was utilized in rumen protein synthesis. Without dietary carbohydrate supplements utilization decreased to 22% (S.D. = 5). Second, ingesta of the rumeno-reticular cavity were replaced with saline; and accumulation of ammonia, representing a hydrolytic product of urea, was measured. Concurrent absorption of ammonia was estimated using arteriovenous urea and ammonia concentration data. Total urea-N transfer, the sum of ammonia-N accumulation and absorption plus salivary urea-N, for sheep was 5.2 mmole urea-N/hr. (S.D. = 0.8), of which 0.3 mmole/hr. was in saliva. Similar results were obtained in the goat.

The mean transport number for AGh in aqueous solution was found to be 0.22 (S.E. = 0.015, n = 27). The variability arising from different sources during the iontophoretie application of drugs was estimated. The estimates were used to obtain the distribution of quantities of AGh likely to be released by particular values of electrical charge. The distributions illustrated that considerable differences are likely to exist between quantities of AGh delivered from different electrodes by the same charge. UREA GONSERVATION BY THE KIDNEY OF SHEEP FED LOW PROTEIN RATIONS K. H. Mclntyre" and V. J. Williams, Department of Physiology, University of New England.Various studies have shown that only small amounts of urea are secreted in the urine of camels^ and sheep-fed diets low in crude protein content. This led to conjecture that the kidney of sheep had a special mechanism for urea conservation when low protein diets were fed. The problem was studied using three diets varying in protein and readily available carbohydrate content. The results showed that the amount of urea excreted in urine was linearly related to plasma urea concentration (P < 0.01), and urine fiow rate (P < 0.01). The minimum amount of filtered urea which was excreted was 10% to 15%, and in all diets urea reabsorption was largely restricted to the proximal tubule. The results suggested that plasma urea concentration, rather than any special kidney mechanism, determined the degree of urea reabsorption by the kidney of sheep fed diets low in crude protein content.