The one-humped camel possesses remarkable abilities to exploit the scanty feed and water supplies found in its natural habitat, the arid and semi-arid areas. However, exaggerated and erroneous claims have sometimes been made regarding the digestive tract of this species, especially with respect to its ability to store and use water efficiently. Nevertheless, the many features peculiar to the camel's digestive system have sometimes led authors to describe the camel not as a "true" but as a "pseudo" ruminant.
Early reports on the digestive system of the dromedary, e.g. by Cauvet (1925), Leese (1927), Droandi (1936) and Tayeb (1950b and c), continue to serve as reference works on this topic. Recently, Schmidt-Nielsen (1964) has confirmed many of these original observations and the present summary, in which the parts of the digestive tract are briefly described one by one, is mainly based on the findings of these investigators.
The lips of the camel are extremely mobile. The upper lip is bifid, a feature thought to aid the consumption of thorny plant material, while the lower one, especially in adults, tends to be pendulous. The upper lip is also sensitive enough to pick up small pieces of vegetation, according to Hafez (1968), who added that the nostrils are surrounded by sphincteric muscles which keep them closed most of the time, thus reducing evaporation from the nose and preventing the entrance of sand and flies. The mouth is often open and gurgling or bellowing sounds are frequently emitted. During this process, a pink bladder-like membrane (part of the soft palate) may be seen to protrude beyond the lips, especially among rutting males. This mucous membrane is protracted less in females than in males. Nevertheless, in both sexes it may appear as a balloon-like structure, although in fact it has no central cavity. It is made of loose connective tissue according to Leese (1927), who concludes that its protrusion is associated with the eructation of rumenal gases. A report by the British Military Administration in Eritrea (BMA, n.d.) indicates, however, that protrusion of the soft palate mucosa may be a mechanism providing for the moistening of the throat, and thus a form of protection against excessive thirst. The camel has a very hard dental pad and a long hard palate.
The cheeks are densely lined by pigmented papillae, long conical protuberances (up to 2 cm) which can easily be mistaken for pathological growths, even by the experienced camelman. The tongue of the dromedary is a small but highly mobile structure supplied with five to seven papillae on each side, each of which can be up to 1 cm in diameter.
The adult dromedary generally has 34 teeth. Sudanese breeds are reputed to have 36. A peculiarity of the dentition is the presence of incisor teeth in the upper jaw and canines in both jaws (Leese, 1927). In this respect the Camelidae differ from other ruminants. The dental formula of the dromedary is:
Leese (1927), Acland (1932), Boue (1950) and Williamson and Payne (1978) discuss the use of dentition in determining the age of camels. Both Acland and Williamson and Payne show that at birth the central pair of teeth has already erupted, at 1 month the laterals appear and by 2 months the third pair erupts through the gum. These teeth are crowded and begin to wear down at 1 year. At 2 years they are so worn that they are no longer crowded or touching each other. By 4 years they are completely worn out, with square or irregular tables, and are loose. At 5 years the central pair of permanent teeth erupts, followed by the second at 6 years, and all three pairs are visible at 7 years.
Although there are minor anatomical differences, the camel's salivary glands resemble those of other ruminants. They include well developed parotid, maxillary and molar glands, and insignificant sublinguals (Leese, 1927). Leese also described minute salivary glands at the base of the cheek papillae. An extensive account of these glands and the associated ganglionic and lymphatic supplies is given by Tayeb (1959b).
The camel pharynx is a long, narrow cavity divided into two chambers (anterior and posterior) by a transverse mucosal fold. The anterior chamber is a favourite site for camel bots (Cephalomyia larvae). Unlike the horse, the camel has no guttural pouches. Its oesophagus is a long tube of large capacity, and while in the horse this tube is often half the size of the trachea, in the camel it can be 1–2 m long. It is lined by glands which secrete a mucus helping to lubricate the often rough forage consumed by the camel.
As a ruminant, the camel has a stomach with four chambers, although there are some reservations as to whether the last two chambers should be classified as separate entities. The rumen or first compartment continues to be a source of controversy owing to its additional anterior and posterior sacs (Figure 7). These sacs are divided into smaller chambers and subchambers by well developed mucosal folds (Schmidt-Nielsen, 1964), the edges of which are made of strong muscular bands. On postmortem examination the rumen often contains a mixture of food, mucus and water. The extra chambers usually hold a smelly, slimy fluid, probably the reason why such names as " water chambers", "water sacs" and "water compartments" have sometimes been applied to them. Their role as major water storage facilities has, however, long been refuted (e.g. Leonard, 1894).
Figure 7. Schematic representation of the alimentary tract of the dromedary.
Source: Adapted from Droandi, 1936.
Their capacity is hardly more than 7 litres, and it is very doubtful whether such a meagre amount could meet the needs of a large animal like the camel. The rumen occupies much of the left side of the abdominal cavity, and may contain ingesta amounting to approximately 11–15% of the animal's body weight, an estimated capacity comparable to that of the cow. These contents are rich (83%) in the water necessary for digestion in ruminants. The extra rumenal compartments contain numerous glands which secrete a product very similar to saliva.
A large opening connects the rumen to the reticulum, otherwise called the honeycomb, second stomach or second compartment. The mucosal surface of the reticulum is fairly similar to that of other ruminants but differs in being glandular. It has a small capacity and its contents are more fluid than those of the rumen. The oesophageal groove of the camel stomach has only one well developed lip.
The omasum (third stomach or third compartment) of the camel does not have the extensive mucosal folds characteristic of the bovine. It is difficult to distinguish the omasum externally from the abomasum (fourth, glandular or hind stomach). The abomasum is lined by 15–20 mucosal folds which are a favourite site for Haemonchus longistipes. It has a well developed pyloric sphincter.
Leese (1927) estimated that the small intestines of the camel are about 40 m long. The common secretory duct of the liver and pancreas is located in the duodenal portion, about 53 cm from the pyloric sphincter. The jejunum occupies much of the right abdominal cavity. Associated with this middle portion are a chain of mesenteric lymph nodes and a further group around the anterior mesenteric artery. The lymphatic supply of the last portion, the ileum, is closely associated with that of the large intestine. The latter is approximately 19.5 m long with a caecum similar to that of the cow, except that its blind end is attached to the mesentery. The colon is larger in its first portion and is coiled in a manner similar to that of the pig (Figure 7). It is enclosed in its own mesenteric fold. Much water is absorbed in this region, where the fluidy luminal contents suddenly change into hard faecal pellets of dung. The rectum forms the terminal portion of the large intestine.
The camel liver is highly lobulated, especially on its ventral-posterior surface. Extensive interlobular connective tissue gives the organ a similar appearance to that of the pig (Leese, 1927). The camel has no gallbladder and the bile duct fuses with the pancreatic duct to discharge by a common opening into the duodenum. The spleen of the camel weighs about 5.5–6.6 kg.
Most camels are raised in arid areas with scanty and unreliable rainfall. These areas are for the most part considered unsuitable for raising crops (Gauthier-Pilters, 1977). Forage growth is usually very sparse and large grazing areas are therefore needed per animal. Great distances often have to be covered in search of drinking water. The fodder grasses and herbs found here grow, flower, fruit and lignify extremely quickly, providing adequate protein and carbohydrates for only a month or so in a year. Thorn and fodder bushes, which utilize more water owing to their larger root systems (Kuthe, 1977), are thus nutritionally more valuable.
The grazing pastures of the desert (northwestern Sahara) have been divided into three ecological types by Gauthier-Pilters (1972). They consist of (i) the ergs, or areas of shifting sands (dunes), (ii) the hammada, or rock-floored desert areas, and (iii) the wadi, or areas of desert streams, usually dry except during the rainy season.
By necessity therefore, most African camels are raised and must survive under harsh conditions of limited natural vegetation, although in a few areas they are also raised on irrigated pastures. Fortunately the food requirements of the African dromedary are modest, and under extreme drought conditions the animal can decrease not only its food intake (Gauthier-Pilters, 1977), but also its metabolism (Ingram and Mount, 1975). Under these conditions the camel adjusts by adopting highly extensive, dispersed and continuous grazing habits even during the heat of the day, and will also consume more thorny and woody plants.
Field (1979a) reported on the ecology and management practices of the Gabbra and Rendille tribesmen of northern Kenya. Using 17,500 records of plant availability collected over 10,000 feeding minutes, he found that the average diet of camels consisted of dwarf shrubs (47.5%), trees (29.9%), grasses (11.2%), other herbs (10.2%) and vines (1.1%).
There was, however, considerable variation in plant types, and between wet and dry seasons within each type. The camel is thus predominantly a browser, although it also grazes on tall, succulent young grasses. The Somali camel is an exception, reputed to be more of a grazer than a browser.
Camels consume many different kinds of plant: Knoess (1976) noted the advantage of the camel over other livestock in the Awash valley of Ethiopia, in that it could utilize a wider variety of local plants, while Matharu (1966) indicated that Indian camels were able to consume many types of feed sometimes considered unsuitable for other herbivores and could live on hard, thorny plants like acacia, which are alleged to be among their favourite species. Camels are capable of ingesting thorns up to 1 cm long. When such plant types are consumed the amount of green matter drops to about 5 kg per day from the normal 30–40 kg associated with young succulent forages, according to Gauthier-Pilters (1974). In a study lasting 2½ years in the Sahara the latter author estimated that a desert camel consumed 2–4 tonnes of DM annually. She also identified some 200 different types of plants consumed by the camel, although no more than 15–20 could be found on any one grazing pasture. Maxwell-Darling (1938) confirmed the wide variety of plants consumed by the Sudanese camel and further noted that the camel was slow in adapting to new plants, although animals used to being handled could easily be introduced to strange forages if hand fed by the owner. Leese (1927) observed in addition that while local camels could avoid the native poisonous plants, it was easy for newcomers to consume and be poisoned by them. Further information on the species consumed by camels may be found in the ecological publications of Le Houerou (1972 and 1974) and Newman (1979).
The carrying capacity of western and northern Sahara pastures was reviewed by Gauthier-Piiters (1974). She found that a 10% cover of Aristida, with an average production of 2.2 t of DM per ha, was enough to support 300 camels for 5 months. With the less productive Panicum turgidum however, only 0.8 t of DM was present, enough for only 80 animals over the same period. These calculations reflect ideal stocking rates, whereas in practice camels are generally raised on less productive pastures and forages, entailing lower stocking rates. Leese (1927) suggested a stocking rate of one animal per 4 ha. When bushes were close together, 2 ha were considered sufficient, even for a nursing animal.
Bremaud and Pagot (1962) studied the physical, nutritional and botanical characteristics of Sahelian pastures together with their carrying capacity. The nutritive values they obtained are shown in Table 5. They found that the protein content of DM varied from 0.86% in the dry season to 6.32% in the rainy season, while that of cellulose was more consistent at 33.67% and 32.92%o respectively. The nitrogen-free extracts were calculated as 54.74% and 47.32% respectively.
Table 5. The nutritive value of Saharan vegetation in different seasons of the year.
End of dry season |
Mid rainy season |
Start of season | ||||
Mar. % |
Apr. % |
Aug. % |
Sept. % |
Nov. % |
Dec. % | |
Water |
9.50 |
8.20 |
75.00 |
74.00 |
51.00 |
48.00 |
Protein |
1.27 |
0.70 |
1.58 |
1.47 |
1.70 |
1.80 |
Fat |
0.68 |
0.55 |
0.42 |
0.45 |
0.71 |
0.69 |
N-free extract |
48.60 |
50.26 |
11.83 |
13.24 |
24.00 |
25.60 |
Cellulose |
31.90 |
31.00 |
8.23 |
9.64 |
16.50 |
18.50 |
Minerals |
7.30 |
9.20 |
2.29 |
2.54 |
4.60 |
5.40 |
Given the general absence of digestibility trials for the plants consumed by camels––although some values can be derived from FAO data compiled by Gohl (1975)––it is hard to establish the exact minimum requirements of the dromedary under varying age, sex, pregnancy and working conditions. Rough estimates only can be obtained by using the results of Bremaud and Pagot (1962), Gauthier-Pilters (1974 and 1977) and the general formulae for estimating the crude protein digestibility (CP2) and total digestible nutrients (TDN) of fresh tropical forage, given by Butterworth and Diaz (1970) as:
CP2 = –18.88 + 39.07 Loge CP
and
TDN = 51.65 + 3.66 Loge CP – 0.25 CF + 6.85 Loge EE.
Alternatively, the nutrient requirements for cattle have sometimes been adopted as standards for use in camel studies. Thus Farid et al (1979) observed that under stress the Egyptian camel needed less water per unit DM intake or per unit body mass (kg0.82 ) than sheep. Camels digested DM and crude fibre better than sheep, but CP was less well digested. Camels recycled more urea per day than sheep.
Thompson (1978) stated that the quantification of feed requirements for animals is a complex matter because of the variety of factors that influence requirements, the criteria for nutritive adequacy, and the variability between and within animal species. Changes in breeding, management, feedstuffs and methods of feed processing constantly influence feed requirements, which as a result should be frequently reevaluated. Regarding supplementary feeding, Childs (1978) discussed some of the factors affecting nutrient requirements, the major ones being:
(a) already existing feed consumption, which is in turn influenced by energy level of the feed and ambient temperature;
(b) inherent differences between male and female animals in given species;
(c) disease conditions and
(d) management conditions.
It is difficult to draw any general conclusions concerning the adequacy of the feed resources discussed above, and for the camel much work remains to be done in this field. However, Gauthier-Pilters (1974 and 1979) indicated that the Saharan camel can derive enough nutritional value for its daily requirements, if given ample grazing time. She noted that free-grazing camels, being hardier, consume less feed than their fellows from the richer semi-arid areas. The animals used in her own work retained their working capacities in, spite of consuming only 10 kg of forage per day. Adopting a 2.5% DM intake level, Field (1979a) obtained a similar estimate of 9.1 kg per day for a Kenyan work camel averaging 363 kg liveweight.
Leonard (1894), Acland (1932) and the British Military Administration in Eritrea (BMA, n.d.) agree that camels are able to derive enough nutrition by grazing and browsing provided they are used for light work only, but that whenever they perform heavy tasks or when forage is not available or is inadequate, extra feeding is imperative. If the animal is being worked the nourishment derived or the time allowed for foraging is often insufficient. In such cases additional feeding is essential, often demanding more organization on the part of the herders or camelmen. The nutritional management of the dromedary thus varies according to location, nature of work and management system.
In Somalia, the experience of Hartley (1979) was that hand feeding of camels is almost unknown, although animals are sometimes brought to agricultural areas to feed on crop residues such as sorghum, cotton stalks, sesame waste and pulse haulms. The amount of work extracted from baggage camels is adjusted (in terms of weight and duration) to feed availability, without any hand feeding.
Ideally camels should be allowed to feed for 6–8 hours a day, with a further 6 hours being allowed for rumination (Williamson and Payne, 1978; Matharu, 1966). Matharu indicates that camels should be grazed in the morning hours and the late afternoon, and be given grain in the evening. Theoretically this would be the ideal arrangement, but it is not practicable for animals in service, which are often working during the cool parts of the day and are only allowed to utilize the hot periods for grazing or browsing. It is nonetheless highly advantageous to allow the camel to forage as much as possible, since it is not only more economical but, as stated earlier, the animal is also able to utilize a wider variety of forage than other domestic species in similar environments.
Whenever salt is not provided, animals benefit from being allowed to spend part of their grazing time on salt-rich pastures, e.g. Atriplex, Salsola and Suaeda spp. (Williamson and Payne, 1978). Often, however, salt is provided in salt pans, or by salting the drinking wells or even feeding salt earth.
Nanda (1957) recommends that a good camelman should be prepared to march 24–32 km per day with his animals, allowing them to graze for 6–8 hours in the process. When long journeys are undertaken, halts should be made in places with good forage. He observes that it is good management to rest dromedaries during the rainy season, allowing them to graze and recuperate. Forages tend to sprout and become plentiful during the rains, a period during which the camel hump (a form of food reserve) also tends to develop and become restored (Leese, 1927).
When forage is sparse camels have to be mobile so as to derive enough nutrients, and should accordingly be allowed longer grazing and browsing times. Gauthier-Pilters (1974) observed that Saharan camels spent 8–10 hours a day grazing, irrespective of whether the pasture was good or bad. The grazing habits of the dromedary allow it to utilize plants within a radius of 20 km of the camp, taking small bites from each plant, a nibbling tendency which also preserves the desert vegetation. Naturally they prefer plant material high in moisture and oxalate. The amount of forage per bite tends to be fairly constant, allowing a rough estimate of green matter consumed by the camel to be made from the number of bites.
Spencer (1973) noted that camels sometimes trot to their daily browse, giving them more time to feed when they reach the spot. During feeding they should be under the strict control of the herdsman, since it is hard to assemble dispersed camels.
Dahl and Hjort (1976) observed that the grazing patterns of camels form a circle made up of a series of smaller loops (Figure 8), rather than the solid circular or elliptical shapes characteristic of cattle grazing. In the case of camels it is the availability of vegetation rather than water which determines for how long camelmen will set up camp. The duration of a camp may vary from 1 day to a few weeks. Torry, cited by Pratt and Gwynne (1977), also confirms that compared to other livestock the camels of the Gabbra travel great distances to and from water. The maximum distances the various kinds of stock may travel to wells, depending on the quality of pasture between the camp and well, are given in Table 6, while Table 7 depicts the typical limits for a damar ( a camp with its surrounding grazing area) for camels, sheep and goats owned by the Kababish in Sudan.
Table 6. Maximum distances covered by livestock to wells.
Good surrounding Pasture |
Poor surrounding pasture | |
Camels |
80 km |
30–50 km |
Cattle |
40 km |
10–15 km |
Smallstock |
50 km |
10–15 km |
Days interval between watering |
Normal year |
Bad year | |||
Radius grazed (km) |
Area grazed (km2) |
Radius grazed (km) |
Area grazed (km2) | ||
Camels |
9–10 |
56 |
9,842 |
96 |
28,490 |
Sheep and goats |
4–5 |
29 |
2,590 |
48 |
7,252 |
Figure 8. The grazing patterns of cattle and camels.
Source: Dahl and Hjort, 1976.
Although supplementary feeding is rare, it is not altogether unknown. Nanda (1957) indicated that while green fodder or chop could be fed to camels at any time of the day, grain is best fed in the evening. The biting habit of camels makes it necessary not to feed more than one animal in the same manger, which also avoids waste from spillage and ensures that even the young and sick get their fair share. Leese (1927) confirmed that green feed was beneficial to sick and debilitated animals, and when fed to animals in service allowed longer working hours. Some of the supplementary rations recommended by Leese (1927) and Acland (1932) are given in Table 8.
Table 8. Some recommended feeding rations for the camel.
Camel type |
Grazing conditions |
Supplementation |
Working Indian or Egyptian baggager |
Fair Poor None |
3.6 kg millet: 8.9 kg straw; 1.8 kg gram; 42 gm salt. 13.3 kg straw, 2.7 kg gram: 42 gm salt. |
Working Somali or Aden camel |
Poor or none |
8.9 kg hay; 1.8 kg Sorghum bicolor; 42 gm salt. |
Riding camel in Aden |
Variable |
11.1 kg karbi; 2.2 kg cottonseed or other oil cake; 10 gal water |
Walking camel |
Good |
No grain, but some salt. |
Trotting camel |
Good Poor |
4.5 kg grain every watering day, with some salt. 2.27 kg grain every day, with some salt. |
Trekking camel |
Variable |
2.27–4.5 kg grain every day, with some salt. |
Riding camels At rest Working |
Available Available None |
2.27 kg grain per day. 3.6 kg grain per day. 4.5–6.8 kg grain per day, with some salt. |
Camels have also been raised exclusively on supplementary feeds or under feedlot conditions. Khatami (1970) reported on the favourable performance of Iranian camels in the latter environment. In one trial animals were given 15–20 kg of a low-priced ration made up of straw, beet, pulp, molasses and barley (with the barley not exceeding 10–15% of the ration). According to another trial the animals were raised on a sugar beet farm. They were ready for slaughter within a short time, females and males having gained 0.95 kg and 1.4 kg per day respectively.
Evans and Powys (1979), ranching in Kenya, have succeeded in raising camels alongside other livestock under ranch conditions. Here the different feeding habits (browsing and grazing) of the various species are exploited to allow two separate stocking rates, while the camel's browse tendencies are additionally beneficial to bush control.
The experience of Leonard (1894) with camels in military service was that:
(a) camels thrive best in their indigenous environment;
(b) their appetites are uncontrolled in lush pastures and they may bloat to death in clover fields;
(c) under very poor pasture conditions their feed should be supplemented with grain, chopped straw, hay or other available forage.
When no forage was available the animals were given 4.5 kg of barley and 9–11.3 kg of chopped straw. Leonard recommended that when grazing is available the amount of supplementary grain should not exceed 3.6 kg, which even then should be fed only when the work load was at its heaviest. This last opinion would confirm the observation cited earlier that camels can derive adequate nutrition from grazing or foraging alone, when the work load is light. If on the other hand neither grazing nor grain was available, then 31.7 kg of chopped straw was fed along with 85 gm of salt three times a week.
How camels survive under harsh conditions is partly explained by Engalhardat and Rubsamen (1979). They indicated that camels do not secrete large quantities of urea. They are capable of recycling 92–97% of the urea formed in the first and second stomachs, as also are llamas on low protein diets. This process is effected in two ways: through the permeability of the rumenal mucosa, and through resorption in the kidney.
The camel's ability to survive long periods without drinking water is legendary, and is fundamental for its survival in arid areas. Leese (1927) observed that this ability to withstand water deprivation varies between breeds and according to the type of herbage consumed, although it can be induced by the judicious training of the animals. He observed that while the large Delta camel of Egypt required water every day, the Somali camel could survive with only one drink in 4 days. Mares (1959) also reported the astonishing ability of Somali camels to abstain from water, concluding that they were able to go for 30 days without a drink, provided the grazing was good. This breed is also capable of spending as little as 1 week a month on good pasture, while the other 3 weeks are spent trekking to and from wells. In a good year the animals may even last from April to December without visiting drinking wells, surviving only on succulent plants and standing pools. Leese (1927) found that Indian camels needed water every other day, while Cole (1975) noted that the Arabian camel drank once a week in the summer, every 7 to 10 days in the autumn and spring, and every 4 to 6 weeks in the winter. Certain types of desert sheep and goats also possess the ability to abstain from water for some time, but their resistance is nowhere near that of the camel.
The period of abstinence is influenced by climatic factors, the quality and quantity of forage and its water content, the age of the animals and the type of work to which they are subjected, according to Gauthier-Pilters (1974) and Schmidt-Nielsen (1964). The former quoted Monod (1955) as indicating that working animals in the Sahara were able to trek 1000 km, i.e. for 20–30 days without drinking water. When air temperatures reached 30–35° C the animals started visiting drinking places, but it was not until temperatures reached 40° C that their drinking rhythm accelerated and became regular. At this temperature the animals drank every 3 to 7 days, depending on the quality of vegetation. When air temperatures fell below 40 ° C, forage usually remained fairly green, so that camels could manage with only one drink every 10 to 15 days. Camels used to being watered frequently do not withstand dehydration as well as those used to long spells without water.
The ability of the camel to refrain from water for long spells should not, however, be overexploited. Animals should be watered whenever possible, and the more work they are required to do, the more drinking water they need. Hassan (1971) carried out a dehydration experiment on dromedaries from Sudan. A 5-year-old animal was kept in an open enclosure for 51 days (November–December) without water. Although it survived on dry grass throughout the experiment, its appetite became capricious near the end. Blood sample analyses revealed a rise in erythrocytes and a drop in leucocytes and haemoglobin, but the packed cell volume (PCV) remained fairly constant. The animal tolerated a loss of 37% of its body weight, a water deprivation level excelled only by the oryx and the addax antelope.
Just as camels can easily go without water for long periods, so also do they find it easy to drink water when it is available. Gauthier-Pilters (1974) observed that when the animal's water loss did not exceed 90–100 litres (which may correspond to 20% of its weight), it regained its original weight within a few minutes of drinking. Furthermore, a strong healthy camel may consume water equivalent to one third of its body weight in 10 minutes. The highest drinking rates observed were 135 litres in 13 minutes and 200 litres consumed over two to three drinking sessions. On average the Saharan camel was capable of drinking 15 litres per minute, not far from the estimate of 100 litres in 10 minutes given by the Institut fur Tropische Veterinarmedizin (Leupold, 1968b). Schmidt-Nielsen (1964) concluded that the camel has enormous drinking capacities and could consume 30% of its body weight in water in a single session. Leese (192 7) gave the average daily water consumption of the Indian camel as 13.6–36.4 litres, which may rise to 90.9 litres for animals which have been deprived for some time. These figures agree with the range of 30–100 litres given for the East African camel by Pratt and Gwynne (1977). Gauthier-Pilters (1974) estimated the daily consumption of the North African camel to be 20–30 litres. In an extensive discussion (1977) of the drinking habits of this camel type, she found that water consumption was closely correlated with feed intake and that the camel's drinking speed is lowered by malnutrition.
The sources of water for the camel are varied. Usually animals are watered from wells dug and maintained by the camel herders. In desert areas during the rainy season, animals may water from the temporary streams, ponds or oases that develop during this time. For housed camels on farms, piped water may occasionally be available. Nevertheless, a major source for the animal is the water content in forage, a source often overlooked but instrumental in enabling the camel to survive long spells without watering per se. Gauthier-Pilters (19 74) noted that the water content of desert forage is more than is generally believed, and estimated that Saharan camels may derive 3–30 litres per day from foraging, depending on the state and locality of the vegetation. Different plants provide different quantities of water, but even in summer desert camels may obtain up to 15 litres of water with their daily food. The water content of shrubs tends to remain fairly constant throughout the year.
Cole (1975) concluded that the camel's ability to abstain from drinking water was not due to its proverbial ability to store it, but rather to its "cooling system". Bulliet (1975) stated simply that camels do not store water, they conserve it. While these assertions are confirmed by the anatomical description given earlier, they indicate only part of an intricate mechanism which has attracted much research in recent years. Schmidt-Nielsen (1959, 1961, 1964 and 1975), Bartha (1971), Richards (1973) and Hardy (1972) provide descriptions of the physiological mechanisms behind water utilization and conservation in the dromedary. Recently, the subject has been reviewed by Ingram and Mount (1975) and the present account is based on their discussion.
Ingram and Mount suggest that the rate of heat loss (H) in an animal is proportional to the rate of heat production (M) and the rate at which heat is being lost from or stored in the body (S), in a relationship designated as:
M = H + S
They indicate that M is always positive but that H and S may be negative or positive, although His more often positive. The relationship between the production, loss and storage of heat indicates the manner in which the heat from metabolic processes is dissipated.
Heat can be stored in the body without loss to the environment, but only up to a certain point, since a rise in body temperature results. When the organism is exposed to high environmental temperatures which change heat loss into heat gain, i.e. when H becomes negative, S will become positive, owing to the combined effects of metabolic heat production and heat gain from the environment.
Heat storage occurs in the dromedary during the daytime, when it is exposed to high temperatures. The animal's body temperature rises several degrees during the day and falls slowly during the night. The camel has sweat glands, but uses them very economically. Thus, according to Schmidt-Nielsen (1964), instead of dissipating all its heat during the hot, part of the day by sweating valuable water, the camel stores heat, allowing its body temperature to rise as high as 40.7°C. For example, a rise of 6°C in the body temperature of a 500 kg animal is equivalent to approximately 2,500 kcal (sp. heat = approx 0.8), the dissipation of which via evaporation would require almost 5 litres of water (sweat). Instead, this heat is lost at night by radiation and conduction.
If the morning temperature falls to a low level, the leeway for heat storage during the following day will be correspondingly greater, postponing the moment at which sweat must be used to prevent a rise above the tolerance threshold of 40.7°C. During periods of dehydration the fluctuation in body temperature becomes marked, falling to as low as 34°C before rising to the 41°C mark, whereas when the animal is watered daily the fluctuations are much smaller (see Figure 9).
Figure 9. Fluctuation of the rectal temperature of the camel under different watering frequencies.
Source: Schmidt-Nielsen, 1964.
A further factor is that, the sweat lost after the upper limit is reached evaporates on the skin rather than the tip of the hair, so that the latent heat of vaporization is drawn from the skin rather than from the atmosphere. A similar mechanism is found in the donkey, although here the upper limit before sweating is not as high as in the camel. Different species develop different ways of avoiding dehydration, some becoming nocturnal while others, like the camel, fluctuate their body temperatures. Desert man adopts loose clothing, which protects him from radiation during the day and from the cold at night. Some additional characteristics which help camels to survive in the arid areas of low water supply are shown in Table 9.
Table 9. Some morphological and behavioural characteristics enabling the camel to survive in various environments.
Environmental stress |
Adaptive mechanism |
1. Solar radiation/reflection |
Long limbs (increasing height from ground) |
2. High temperatures |
Hair shedding in summer |
3. Seasonality of feed availability |
Adipose tissue reserves (hump) |
4. Deserts-thorny vegetation |
Thick skin, hard tissue around mouth, thick mouth lined with long papillae |
– water scarcity |
Increased drinking capacity, conservation of metabolic water, ability to survive dehydration (metabolism lowered) |
5. Low temperatures |
Low renal flow during dehydration, renal resorption of urea, can feed without water, thick coat in winter |
6. Evaporative cooling |
Apocrine sweating |
Other adaptive mechanisms of the camel include its metabolic activity, which is sensitive to temperature fluctuations, and its kidney structure. The kidney is made of short and long Henle loops, but the proportions of each vary between different species. The more long loops there are the higher the water resorption potential and the ability to concentrate urine. Cattle have more short loops than long, while sheep have more long ones, with the result that the upper concentration limit of cattle urine is only 2.6 osmoles/litre, while that of sheep is 3.5–3.8 osmoles/litre (Macfarlane, 1968). However, these are concentrations during water deprivation, whereas normal values rarely rise above 1.5 osmoles/litre. Thus, while cattle tend to produce a diuresis after drinking, sheep require a considerable intake (3% of their body weight) before increased urine excretion occurs. Camels, however, can retain water without a diuresis. They have a low initial glomerular filtration rate of about 60 ml kg–1 min–1, falling to 15 ml kg–1 min–1 when water is restricted, whereas in cattle, filtration rates of 90–150 ml kg–1 min–1 are found, falling to one third of this value during water deprivation. Sheep are intermediate between the above values.
The camel's ability to concentrate its urine enables it to tolerate water and plants with a high salt content. Richards (1973) notes that the camel is capable of secreting urine with a salt content higher than that of sea water. The urinary bladder of the camel is small. A 300 kg camel watered daily excretes an average of 3 or 4 litres of urine per day, but under half a litre when deprived of water, according to Schmidt-Nielsen (1964). The latter author noted that the volume could be increased to 1 litre by feeding sodium chloride (common salt). With a urine (U) osmotic concentration of 2.760 osmolar, and a normal plasma (P) level of 0.34, camel urine has a total concentration value eight times that of plasma. In other words, the U/P ratio is 8, whereas in man it is 4.
The low rate of faecal dehydration in the camel is also worth noting. The amount of faeces varies with feed composition and digestibility. Generally camel faeces consist of a large number of small, oblong pellets (about 3 cm long). They are very light in weight and their outside is shiny and almost black (Schmidt-Nielsen, 1964). They are so dry that in treeless areas they can rapidly be used for fuel. They burn readily, owing to their abundant cellulose content.
The role of the camel's hump in water storage is not as great as was once believed. Schmidt-Nielsen (1964) argues that while the camel hump contains fat which is convertible to about 40 litres of water, optimum utilization of this source would necessitate the use of oxygen. The oxygen inhaled would lead to a loss of water on the outbreath greater than the water storage capacity of the hump, so that. he doubts the use of the hump reserve as a major source of water for the animal.
There are a number of behavioural factors which are thought to contribute to the conservation of water. For example, Gauthier-Pilters (1979) observed that camels tend to remain lying down in the same spot from early morning, when the ground is still cold. They tuck in their legs while lying down, while other animals tend to spread out. Camels often align themselves with the sun's rays, only shifting position to maintain this orientation. They also tend to huddle together in one large group, as if in an effort to form a single organism with only its dorsal surface exposed.
However, it is the animal's ability to fluctuate its body temperature and withstand high dehydration levels which are the main factors in its tolerance of water deprivation. The camel can withstand body weight losses of 30–40% (Hassan, 1971; Gauthier-Pilters, 1975; Matharu, 1966; Schmidt-Nielsen, 1964). When water is available the camel will quickly drink to replace losses, showing few signs of stress. According to Leupold (1968b), no haemolysis of the blood occurs after heavy drinking of this kind. The erythrocytes of the camel were able to increase to over 200 times their normal size. The camel also possesses the ability to maintain a constant plasma volume throughout periods of fluctuation in drinking water availability. Leese (1927) noted, however, that camels can sometimes die of distension after long and heavy drinks.
