The yield and quality of milk produced by an animal depend on the composition of the feed available, including liquids. The lactating camel in an arid area must not only overcome the shortage of drinking water, but also the shortage of forage. The fodder that is available can also affect the composition and taste of the milk. When camels subsist mainly on Atriplex, the milk acquires a salty taste, while feeding on Schowia purpurea gives the milk an odour similar to that of cabbage (Gast, et al., 1969). Fodder composition also directly affects the fat and protein content of the milk. The availability of drinking water was shown to have a direct affect on milk fat content, with limited drinking water causing a decrease in milk fat and protein content (Yagil and Etzion, 1980a).
One of the most advantageous attributes of the camel in drought areas is its ability to utilize plants that grow well under arid conditions and are in the main unacceptable to other grazing animals (Knoess, 1977; Sharma and Bhargava, 1963; Williamson and Payne, 1965). Examples of such plants are the camel thorn, Acacia and salt bushes (Newman, 1979). The utilization of available fodder is also much higher in the camel than in any other domestic animal in the same areas (Farid, et al., 1979). The camel's ability to utilize the scanty fodder resources of the arid zones of the world for body maintenance, growth and production makes this animal a potentially important source of food. An understanding of the anatomy and physiology of the digestive tract and of feed utilization is therefore, important before consideration is given to the value of these animals as a source of human nutrition.
The digestive tract
Although camels ruminate they are not true ruminants, as they lack the four well-defined stomachs of the ruminants; the rumen, reticulum, omasum and abomasum. The anatomy of all members of the Camelidae is considered to be similar but most of the available data on the anatomy of the alimentary canal have been obtained mainly from the llama.
Lesbre (1903) and Leese (1927) stated that the camel has only three stomachs, compared with the bovine's four compartments (Phillipson, 1979) a.i. the missing compartment being the omasum, or third stomach. Hegazi (1950) describes the camel as having the same four compartments as other ruminants, but with the external constrictions between the omasum and abomasum being less well defined in the camel. Vallenas, et al., (1972), state that the llama and guagnaco stomachs consist of only three compartments. The anatomy of the stomachs will be discussed in detail later.
The salivary glands of the camel have the same grouping as in cattle, but are slightly darker in colour (Leese, 1927). The arrangement of the glands, however, is different. The parotid glands are in the same position in camels as in cattle, but in camels the maxillary gland is located under the parotid gland and jugular vein and over the pharyngeal lymph glands (Leese, 1927). The gland does not extend under the throat as it does in cattle. The sublingual glands are smaller than those of cattle and are situated along the root of the tongue. The buccal glands are well developed, and have dorsal and ventral portions.
When comparing the mouth of the camel with that of cattle, the outstanding differences are the very supple lips of the camel, the long prominent papillae, and canine teeth.
Much has been written about the internal anatomy of the camel stomachs. The stories of camels being slaughtered for water in the stomach (Bohlaken, 1960) led to the belief that the rumen, contained water cells (Leese, 1927). It was assumed that these water cells were able to store water (Colbert, 1955; Hegazi, 1955; Leese, 1927). This theory was disputed by Schmidt-Nielse, et al. (1956). The saclike compartments are found in the caudal part of the first compartment, the rumen (Vallenas, et al., 1972). It has been suggested that the main function of this glandular region of the fore-stomach is the rapid absorption of solutes and water (Engelhardst and Rubsamen, 1979).
The suggestion that the glandular areas of the rumen are accessory salivary glands (Schmidt-Nielsen, et al., 1964) has not been substantiated. The mucous layer which covers the surface epithelium may have a mainly protective function (Bubsamen and Engelhardt, 1979). The bicarbonate secretion of these glands (Eckerlin and Stevens, 1972) was not substantiated in later experiments (Rubsamen and Engelhardt, 1978).
The oesophagus enters the rumen (Vallenas, et al., 1972). This compartment is divided by a transverse muscle pillar into a cranial and caudal sac. The second compartment, the reticulum is small and only partially separated from the first compartment. The reticulum is separated from the third compartment by a tubular sphineter. The third compartment is an elongated tubiform organ, slightly dilated at its proximal end where it enters the fourth chamber, which its fundic and pyliric glands. The mucous membrane of the third compartment contains long folds and no laminae, as found in the typical bovine omasum (Bohlken, 1960). The fourth compartment, the abomasum, is small. In adult animals no folds are found (Bohlken, 1960).
The surface of most of the first and second compartments is lined with a non-papillated stratified, squamous epithelium (Vallenas, et al., 1972). Glandular epithelia can be found in the ventral portions of the first two compartments and covering all of the third compartment. The glandular area in the first compartment is restricted to the bottom of the saccules, and this may be the reason for this area being smaller in camels than in llamas. In addition, the pouches in the camel's rumen are smaller than those in the llamas.
In the adult llama the contents of the first two compartments account for 10–15 percent of the animal's body weight, and the third compartment for a further 1–2 percent. It is therefore clear that the intestines must contain at least an additional 5 percent of the body weight. Then the total contents of the camel's alimentary canal will account for 25 percent or more of the animal's body weight. The liquid contents in the alimentary canal is the source of water for the thirsty camel (Yagil and Etzion, 1979).
The function of the numerous endocrine cells in the stomach wall (Engelhardt and Rubsamen, 1979) is unknown but it is possible that these cells play an important role in the control of the water and electrolyte balance of the camel during dehydration (Yagil and Etzion, 1979).
From the anatomical differences between the Camelidae and Bovidae it was hypothesized that the physiological processes in the alimentary canal would also differ (Bohlken, 1960). This is further emphasized by the difference in rumen protozoal population between the camel and the sheep (Farid, et al., 1979). Entodinium comprises 70 percent of the rumen protozoal population in both animals, while Holotricha accounts for 10 percent of the population in sheep, but was absent in camels.
Epidinium is present in camels, but absent in sheep rumen. The interesting fact was that during water restriction the Entodinium population and total protozoal count decreased in sheep, but in camels the Entodinium population increased and the total count remained virtually unchanged.
Physiology of the digestive tract
The extremely mobile lips of the camel and the tough mucosa of the mouth enable the animals to graze thorn bushes. The branches are stripped of their leaves and the thorns present no problem.
In the mouth the feed is mixed with saliva. The size and structure of the salivary glands and the composition and flow of saliva from the glands, are all comparable with what is found in cattle (Engelhardt and Rubsamen, 1979). Camel saliva is slightly hypotonic and the bicarbonate content is high (Engelhardt and Rubsamen, 1979). When the animal is dehydrated a quarter of body weight is lost. The parotid gland secretions then decline to a fifth of the normal flow (Hoppe, et al., 1974). In the camel, as in all ruminants, the urea formed from the protein metabolism is recycled to the stomach via the saliva. In addition, the camel also obtains urea via the rumen epithelium itself (Houpt and Houpt, 1968; Nolan and Leng, 1972). The urea nitrogen is important as it is assimilated into microbial protein which is a source of protein for the animal following hydrolysis in the small intestines (Emmanuel, 1979).
Camel saliva was collected by allowing the animals to chew a clean dry sponge and then examined for amylase content (Nasr, 1959). It was found that the saliva has less amylase than that of man, pig or rat. This, however, is different from cattle saliva which has no amylase (Schwarts and Steinmetzer, 1924) whereas it is present in buffalo saliva (Nasr, 1959). Of all the glands, the parotid glands have the most amylolytic activity, the submaxillary glands the least and the sublingual glands none being mucous glands.
The contractions of the first and second compartments begin with a contraction of the second compartment (Engelhardt and Rubsamen, 1979). This is similar to the relationship of reticulum and rumen in cattle. In camels the contents of the dorsal portion of the rumen are relatively dry. The ventral portion of the cranial and glandular sacs in the reticulum, contain semifluid and watery ingesta (Ehrlein and Engelhardt, 1968; Ehrlein and Engelhardt, 1971; Vallenas and Stevens, 1972).
Following the first, single contraction of the reticulum there is an immediate contraction of the caudo-ventral region of the rumen and the glandular sacs (Engelhardt and Rubsamen, 1979). The caudo-dorsal rumen contracts, followed by the cranial sacs. This first set of contractions is followed by additional contractions. The duration of a cycle is 1–2 minutes in the resting llama. The rate increases when the animal feeds. The contractions and movements of each cycle begins with a contraction of the reticulum. During contraction of this compartment contents are moved from the reticulum to the caudal sac of the rumen. From here part of the contents re-enter the reticulum and part goes into the cranial sac, when the caudal sac contracts. When the cranial sac contracts, its contents move back into the caudal sac (Ehrlein and Engelhardt, 1968). The motility of camel's fore-stomach is radically different from that of cattle.
The contents of the third compartment, the omasum, are fairly dry. This strongly suggests a significant absorption of water (Engelhardt, Ali and Wipper, 1979) although water is also squeezed into the abomasum when the omasum contracts. Stomach contents enter the third compartment, when the canal between this compartment and the first compartments, dilates. This occurs when there is a maximum contraction of the reticulum. At this stage the proximal portion of the canal contracts, while the distal part dilates. The whole canal contracts, pushing the contents through to the third compartment. As water is absorbed in this compartment, it functions in a manner similar to the bovine omasum (Ehrlein and Hill, 1969; Stevens, et al., 1960). In the third compartment weak circular contractions occur in the proximal portion with pronounced contractions in the distal portion (Ehrlein and Engelhardt, 1971).
Rumination and eructation occur three to four times during every cycle (Ehrlein and Engelhardt, 1971; Engelhardt and Rubsamen, 1979). Rumination begins after the maximal contraction of the cranial rumen sac. Eructation takes place near the peak of the caudal sac contraction.
In the camel's fore-stomachs the volatile fatty acids (VFA) produced are efficiently neutralized, probably by the glandular secretions (Vallanas and Stevens, 1972). A high concentration of VFA is found in the Camelidae rumen (Maloiy, 1972; Vallenas and Stevens, 1972; Williams, 1963). The various proportions of VFA are similar to those found in the rumen of cattle (Maloiy, 1972). This suggests a great similarity in metabolism in the forestomachs of camels as compared with other ruminants. Motility studies, however, indicate that there is no precise similarity between the species (Vallenas and Stevens, 1972) and was verified in comparison studies between the camel and the Zebu (Maloiy, 1972). It was found that the camel has a lower digestive efficiency of low quality hay, assumed to be caused by a more rapid passage of food through the stomachs. Camels fed on straw (Yagil and Etzion, 1980), however, not only grow better but digest the food better than milch cows (Personal observation). Digestibility of medium quality hay was no different in the llama and in sheep (Engelhardt and Schneider, 1977). In the digestive studies the most important finding was that the fluid volume of the fore-stomach and the rate of outflow of fluid from the stomachs to the intestines was far greater in the camel than in the Zebu (Maloiy, 1972). Water-deprived sheep lost far more rumen water than camels (Farid, et al., 1979). Water dynamics in the alimentary canal of the camel allow it to survive and produce during dry periods. The alimentary water provides a reservoir that is tapped slowly in order to maintain a relatively unchanged extracellular volume and provides the fluid which dilutes the milk. (Yagil and Etzion, 1979; Yagil and Etzion, 1980a and b). The anatomical differences between camels and other ruminants could account for the much slower water turnover in the camel (Macfarlane, 1977).
Sodium chloride, and VFA were found to be rapidly absorbed from the rumen of the llama (Engelhardt and Sallman, 1972; Rubsamen and Engelhardt, 1979). The absorption rates in the llama were three times greater than the absorption in sheep and goats. Absorption occurs mainly in glandular areas of the fore-stomach. In the third compartment solubles and water are absorbed (Engelhardt, Ali and Wipper, 1979). The absorption rates of sodium, VFA and water in this tubiform compartment were found to be far greater than the absorption rate in the omasum of sheep and goats.
The pH is very low in the abomasum (Engelhardt, Ali and Wipper, 1979). An estimated secretation of water occurs reaching 15 percent of the amount that was absorbed in the omasum.
Comparative experiments carried out at the Desert Research Institute in Egypt (Farid, et al., 1979) showed that the camel managed far better than sheep on a low-protein, roughage diet and restricted drinking water regimen. The sheep were allowed to drink every three days, the camels every twelve days. The camels needed less water than the sheep for every unit of dry matter consumed or per unit body mass. The camels also had a lower water intake than Zebu cattle (Maloiy, 1972). During deprivation studies, camels lost far less water in urine and feces than did sheep (Farid, et al., 1979). The camels digested dry matter and crude fibers better than the sheep. The sheep, however, utilized crude protein better than the camels. The sheep increased their feed intake during dehydration. The nitrogen metabolism of the camel was superior, and this was even more apparent during water restriction owing to the reduced nitrogen excretion in both faeces and urine. The sheep were only able to reduce the nitrogen excretion in urine. The endocrine cells and secretory cells in the rumen of the camel could account for the added nitrogen retention capabilities (Engelhardt and Rubsamen, 1979). These data also reinforce the theory of endocrine control of the alimentary canal, kidneys and mammary glands affecting the water, salt and nitrogen metabolism (Yagil and Etzion, 1979; Yagil and Etzion, 1980a and b), the ADH being responsible for the flux of water and urea-nitrogen, the aldosterone for the flux of sodium. The decline of nitrogen in both faeces and urine and the renal loss of sodium allow the camel to maintain a relatively unchanged extracellular volume. The flow of water in the same direction with the urea-nitrogen accounts for the lower amount of feacal and urinary water in the camel, when compared to the Zebu steer (Maloiy, 1972) or sheep (Farid, et al., 1979). The camel has thus a far more efficient nitrogen conservation mechanism than other ruminants (Emmanuel, 1979). Even on a low-protein diet, nitrogen fixation in the rumen and constant recycling of urea contribute significantly to a steady protein synthesis. Twelve days of dehydration in the camel were equal to two days of dehydration in sheep, as far as recycling of urea was concerned (Farid, et al., 1979). The most pertinent result of the experiment was that the sheep did not survive the experiments while the camels were unaffected.
Another important difference with other ruminants is that camels have a significantly higher blood glucose level (Emmanuel, 1979; Yagil and Berlyne, 1977). This may be caused, in part, to the anatomical differences in alimentary canals (Engelhardt and Rubsamen, 1979), although VFA production was high in the camel's fore-stomachs (Engelhardt and Rubsamen, 1979; Maloiy, 1972). Other metabolic factors may play a role in the glucose handling by the camel as well as the hygroscopic properties of glucose may play a significant role as was demonstrated in glucose-loading trials (Yagil and Berlyne, 1977).
Salt makes up a very important part of the camel's diet (Hartley, 1979). Nomadic tribes are especially careful to ensure that the camel obtains sufficient salty plants to eat. Salt is an important factor in the passage of water and urea in the gut and the kidneys (Yagil and Etzion, 1979). Inadequate salt diet will lead to less milk production in camels (Hjort and Dahl, 1979; Mares, 1954) which becomes even more important when drinking water is restricted (Yagil and Etzion, 1980).
The camel covers large areas while browsing and grazing, and is continually on the move, even if food is plentiful. Distance of 50–70 kilometers a day can be covered (Newman, 1979). Camels in the Horn of Africa still range for their food even though they are brought to graze on crop residues, such as sorghum stover, cotton stalks and sesame waste (Hartley, 1979).
The main forage is obtained from trees and shrubs. The diet is made up of species of Acacia, Indigofera, Dispera, and Tribulus. The Acacia, Salsola and Atriplex plants which contain the highest content of moisture, electrolytes and oxalates are preferred (Newman, 1979). It is noteworthy that most of the preferred plants are not readily eaten by other animals because they are thorny and bitter. In Australia (Newman, 1979) sbrubs and forbs make up 70 percent of the diet in winter and 90 percent in the summer.
In northern Kenya some of the plants browsed by camels are (Maloiy, 1972):
|Botanical name||Water content (g/100 g)||Crude protein (g/100 gDm)||Caloric value (cal/gDm)|
|Acacia brevispica (flower)||58||17.8||3 958|
|Acacia brevispica (fruit)||74||23.5||5 720|
|Acacia mellifera||65||18.4||4 472|
|Acacia senegalensis||67||13.0||4 027|
|Acacia tortilis||64||13.6||4 550|
|Capitanya sp.||88||16.3||4 007|
|Duosperma eremophilus||73||16.6||2 746|
|Kleinia sp.||78||7.3||4 385|
The camels graze in the early morning and late afternoon which are the coolest times of the day for feeding. Analysis of the fodder indicated that the plants had a high water and protein content.
Raedeke (1980) gave a detailed account of the food habits of the guagnaco in Chile. The average diet consisted of 61.5 percent grass-like forage; 15.4 percent browse; 6.9 percent epiphytes; 2.4 percent lichens; 2.6 percent fungi; 11.2 percent forbs. Browse was the least preferred forage, while euphorbs, lichens, epiphytes and fungi were the most preferred. The availability of the plants also determined their degree of intake. Essentially the South American Camelidae prefer succulent forage (Newman, 1979). Whereas camels prefer shrubs and forbs, cattle and buffaloes prefer grasses (Newman, 1979). Thus, the cattle and camels complement each other and do not compete for food when grasses, shrubs and forbs grow in the same region. This is not the case with sheep and goats, which have more or less the same preferences as the camels. Even then, a certain symbiosis can be obtained. Feeding trials with Atriplex sp. grown densely were not a success with sheep (Budda, personal communication). Sheep ate only around the perimeter of the trial area. Any attempt to penetrate the bushes resulted in the wool being caught on twigs and thorns. When camels grazed the field, their natural habit of wandering while eating opened up paths for the sheep to follow and benefit from the abundant food. This trial showed the possibility of growing fodder in large amounts in small areas, and showed the benefits of raising sheep with camels. This combination of communal grazing was also demonstrated in Kenya (Evans and Powys, 1979). Between the years 1974–1978, camels were introduced into sheep and cattle grazing areas. The Productivity of the land was increased as camels ate vegetation ignored by other animals. The pasture was also improve when the plants, which competed with the grass, were removed.
Camels have been successfully grazed on pure Alfalfa and overmature Panicum maximum in Ethiopia (Knoess, 1976; Knoess, 1977). It is not practical to consider these species as forage for camels in dry areas. When camels and sheep were presented with a mixture of chopped hay and straw, the sheep chose the hay, while the camel ate both without showing preference (Farid, et al., 1979).
Camels manage to store sufficient energy in hump fat during the season when food is plentiful, to enable them to survive the times of poor forage (Hira, 1947). The problem of ranching animals in arid and semi-arid areas is the seasonal low availability of forage and water (Payne, 1966). The distances covered by grazing camels is one of the reasons for the decline in their numbers. Not only is family life disrupted by separation of the herders from the family, but encroaching urbanization is causing conflict between camel herders and settlers. Urbanization is also causing the destruction of the natural grazing. In critical areas the camel was accused of causing severe damage to slow-growing trees and shrubs, although sheep and goats are either the culprits or are at least partially to blame (Warrent and Maisels, 1977). Newman (1977) suggests that the feeding habits of the camel are such that they actually preserve their environment. Competition with other grazing animals presents a danger to the camel (Raedeke, 1980). In addition, various native ranges in Africa are being depleted of natural forage (Le Houerou, 1974) as a result of the inhabitants giving up or replacing camel raising with quick-return cash crops, industrial crops, grains and vegetables. Not only does this lead to famine in time of drought, but natural drought-resistant plants and shrubs have disappeared, and so there are no animals to supplement human diet.
To summarize, not enough is known about the anatomy and physiology of the one-humped camel, especially its activity during periods of drought. The camel can subsist on forage rejected by other animals and are unaffected by long periods without drinking water. Milk production is relatively unaffected by the lack of water (Yagil and Etzion, 1980b), but the smell, taste and content is affected by the type of forage as well as by lack of water (Gast, et al., 1969; Yagil and Etzion, 1980a). The camel's grazing habits and its preferred native ranges are bringing it into confrontation with the changing manner of living and the striving for quick-profit farming. This is disastrous in arid areas, where these quick-turnover crops have an adverse affect on the human population when the lack of rainfall precludes agriculture activities. When famine becomes widespread and people are starving, the camels although not being a rapidly reproducing animal, would provide a suitable and continuous supply of food during periods of drought.