III. COMPOSITION OF CAMEL MILK

In the previous section it was shown that camels can produce an adequate amount of milk in drought areas where other domestic animals have very low production. Of prime importance for the young camel, and especially for man, who drinks the milk, is the composition. Cows exposed to heat, especially if drinking water is scarce, produce milk that has a much higher dry-matter content than normal (Bianca, 1965). The fat content is especially high. This milk would certainly not provide a suitable diet for man or animal exposed to the same climatic and water stresses. Data concerning the composition of milk vary greatly. This can be partly attributed to the inherited capabilities of the animals, but the stage of lactation, age, and the number of calvings also play a role. Of special significance to the quality of the produced milk are the feed and water quantity and quality.

Most camel milk is drunk fresh. It is also consumed when slightly sour or strongly soured. (Milk products will be considered in a separate section). Camels'milk is generally opaque white (Dihanyan, 1959; Heraskov, 1953; Yagil and Etzion, 1980). Normally it has a sweet and sharp taste, but sometimes it is salty (Rao, 1970). At times the milk tastes watery. In certain countries there are prejudices among the urban population concerning camel milk. It is considered as having an unpleasant taste (Yasin and Wahid, 1957). It is frothy when shaken slightly (Shalash, 1979). The changes in taste are caused by the type of fodder and the availability of drinking water.

Fresh camels' milk has a high pH (Grigor'yants, 1954; Ohri and Joshi, 1961a). The pH of milk is between 6.5–6.7 (Shalash, 1979). This is similar to the pH of sheeps' milk. When camel milk is left to stand, the acidity rapidly increases (Ohri and Joshi, 1961). The lactic acid content increases from 0.03 percent after standing 2 hours to 0.14 percent after 6 hours.

The first milk, the colostrum, is white and slightly diluted as compared with the colostrum of cow (Yagil and Etzion, 1980). Other studies on the composition of the milk, depending on the stage of lactation, confirm these data (Sestuzheva, 1958). It was found that 3 hours post-partum total solids (T.S.) averaged 30.4 percent. The T.S. declined to 18.4 percent during the first 2 days of lactation. This decline in T.S. was not caused by a variation in fat content, as initially the fat percentage was low, at 0.2 percent, and then greatly increased to 5.8 percent; rather the decline in total proteins and minerals was responsible. Ohri and Joshi (1961b) made a detailed study of camel colostrum. The range and average values for colostrum were:

In Somalia the colostrum (dumbar) is used by some as a food, but is generally only taken as a laxative (Mares, 1954). However, in most countries where camels are kept, the colostrum is considered unsuitable for drinking (Shalash, 1979). It is even considered as unsuitable for the calf and is milked onto the ground. However, as colostrum contains large amounts of antibodies and is beneficial for digestion in the newborn calves, it is advisable to use it for the calves, if it is not palatable for human consumption.

The general composition of camels' milk in various parts of the world is given in Table 3. Milk analysed at monthly intervals until the 6th month of lactation, then analysed in the 12th month, and at the end of the 14–17 months total lactation period, showed that the average composition observed during the first month of lactation remained constant for the first 6 months (Sestuzheva, 1958).

The specific gravity of camel milk is less than that of cow, sheep or buffalo milk (Shalash, 1979).

The most important factor in camel milk is water content. Young camels, and especially the humans living in drought areas, are in need of fluid to maintain homeostasis and thermoneutrality. The water content of camel milk fluctuates from 84 percent (Knoess, 1976) to 90 percent (Ohri and Joshi, 1961). When examining only the effects of the lack of drinking water on camel milk, the diet remaining unchanged throughout the year, great changes in water content of milk were found (Yagil and Etzion, 1980). The camels were allowed ad libitum drinking water only during the winter. From spring until the end of summer the mothers and calves were allowed to drink only once a week for one hour. With water freely acessible the water content of the milk was 86 percent, but when water was restricted the water content of milk rose to 91 percent. These changes reflect the range presented in the literature and thus makes it important as to when the milk was sampled by the various investigators. Water content of fodder would also affect water content of milk. Thus, it would appear that the lactating camel loses water to the milk in times of drought. This could be a natural adaptation in order to provide not only nutrients, but necessary fluid to the dehydrated calf. Another explanation can be found when examining the mechanism of sweating in man when exposed to heat (Ingram and Mount, 1975). Adaptation to heat causes secretation of a profuse watery sweat. This is caused by secretation of endogenous ADH (anti-diuretic hormone, secreted from the neurohypophysis) because man prouces the same water sweat when injected with ADH. Thus man loses water from his sweat glands, allowing him to maintain thermoneutrality. As the mammary glands have the same embryonic origin as the sweat glands (Strauss, 1974), and as ADH secretation is elevated in the dehydrated camel (Yagil and Etzion, 1979), it could happen that the loss of water into the milk is due to the action of this hormone. Injections of ADH into lactating laboratory rats exposed to heat for 8 hours a day also caused increased water content in milk (Etzion and Yagil, 1981). Even the milk of slightly dehydrated cows, not under desert conditions, shows such an increase (Aschaffenburg and Rowland, 1950). It is also of importance to note that the other hormone of the neurohypophysis is oxytocin, the hormone that is essential for the letdown of milk. Stimulation of suckling and milking could possibly influence the neurohypophysis and induce secretion of both hormones and so lead to a dilution of the milk. Whatever the explanation, the diluted milk at times of water deprivation makes an excellent food for man. It also explains the Bedouin tales of taking a lactating camel along on long trips through the desert (Abu-Rabuja, personal communication).

Table 3. General compistion of camel milk

* Non-fat solids

With the increase in water content of milk produced by thirsty camels, there was a decrease in the fat content, from 4.3 to 1.1 percent (Yagil and Etzion, 1980). In the literature, the percentage of milk fat of camels varies from 2.6 (Yasin and Wahid, 1957) to 5.5 (Knoess, 1976). Again, the hydration status of the animals would determine the fat content of the milk, as well as the type of forage eaten.

The milk fat is also different from that of other animals. When left standing, fat is distributed as small globules throughout the milk (Yagil and Etzion, 1980). The fat globules are very small 1.2–4.2 microns in diameter (Dong Wei, 1981). The ratio of fat to total solids averages 31.6 percent (Shalash, 1979). This is much lower than that of the buffalo, which is 40.9 percent. The fat appears to be bound to the protein (Khan and Appara, 1967). This would explain why it is difficult to extract fat by the usual method of churning sour milk (Rao et al., 1970). This difference in milk fat necessitated saponification of camel milk in order to extract vitamin A and carotene (Khan and Appana, 1967). Petroleum ether extraction, as used in milk of other animals, was not efficient enough for for camel milk.

Camel milk fat has a low Reichert value of 16.4 (Dhingra, 1934). The fatty acid composition of camel milk fat was found to be as follows (in weight percentage):

Compared to cow, buffalo and ewe milk fat, camel milk fat contains less short-chained fatty acids, but the same long-chained fatty acids can be found. (Dhingra, 1934). Gast et al., (1969) claim that the value of camel milk is to be found in the high concentrations of volatile acids and, especially, linoleic acid and the polyunsaturated acids, which are essential for human nutrition.

The molar percentage distribution of the glycerides in camel milk fat is as follows (Dhingra, 1933).

The total saturated acids in whole fat was 62.6 percent mole.

The distribution of phospholipids in camel milk (expressed in mole percent of phospholipids) was as follows Morrison, 1968 a and b):

Milk protein content of camel milk ranges from 2 to 5.5 percent (Yasin and Wahid, 1957). The total protein in camel milk is similar to that of cow milk. Dilanyan (1959) reported the casein content of dromedary and Bactrian milk as 2.7 and 0.89 percent respectively and that of albumin as 3.8 and 0.97 percent respectively. Kherashov (1961) examined four breeds of camels and found the value for total protein to vary from 3.5 to 3.8 percent and casein from 2.7 to 2.9 percent. Egyptian camels had low casein, 2.6 percent (El-Bahay, 1962). Camel milk casein and their fractions were found to be poor in crude protein when compared with cow milk (Pant and Chandra, 1980).

Milk from the dehydrated camel has a severely decreased protein percentage. (Yagil and Etzion, 1980). Again, this demonstrates the direct effect of drinking water on the composition of milk. It must be stressed that protein content of the feed will also directly affect that of milk.

The amino acid composition of Bactrian milk declines as lactation advances (Kudabaer et al., 1972). The contents of methionine, valine, phenylalanine, arginine and leucine are greater than in cow milk. The nitrogen content of camel milk was found to be 15.6 gr/100 gr. The following amino acids were present: alanine 3.05; arginine 3.15; asparagine 7.65; glycine 1.57; glutamine 23.4; histidine 2.5; isoleucine 6.4; leucine 10.4; lysine 7.6; methionine 3.5; phenylalanine 5.7; proline 13.3; serine 5.9; threonine 6.9; tyrosine 5.8; valine 7.4; ammonia 1.72. (Hoeller and Hassa, 1965).

Sestuwheva (1958) found that the lactose content of camel milk remained unchanged from the first months up to the end of lactation. The concentrations in milk vary from 2.8 percent (Grigor'yants, 1950) to 5.8 percent (Yasin and Wahid, 1957). These were approximately the same range as found between the hydrated and dehydrated animals (Yagil and Etzion, 1980). The changes in lactose concentration would account for the milk being described as sometimes sweet, and other times bitter.

The mineral content of milk is expressed as total ash in Table 3 and will be discussed further. The total ash content of camel milk varies greatly, and the lowest percentage of ash was found in the milk produced by dehydrated camel (Yagil and Etzion, 1980). Camel milk is rich in chloride (El-Bahay, 1962). Although milk from the dehydrated camel showed decrease of fat, protein and lactose content, that of sodium and chloride increased (Yagil and Etzion, 1980). This would account for the salty taste.

Both concentrations of calcium phosphate and magnesium decline in the milk of dehydrated camel. (Yagil and Etzion, 1980). However, these concentrations are still adequate for human nutrition and are similar to the values presented by Kulier (1959).

Camel milk is rich in vitamin C (Kno, 1959, Knoess, 1979). This is important from the nutritional stand point in areas where fruit and vegetables containing vitamin C are scarce. Kheraskov (1961) found the vitamin C content of camel milk to vary between 5.7 and 9.8 mg percent. As lactation progresses, the vitamin C content increases (Bestuzheva, 1964). The vitamin C levels are three times that of cow milk and one-and-a-half that of human milk (Gast et al., 1969). Vitamin B₁₂ in camel milk declined from 3.9 ug/l at 1.5 months lactation to 2.3 ug/l at the fourth month of lactation (Bestuzheva, 1964). Vitamin B₁ and Vitamin B₂ concentrations are adequate and are higher than those of Afar sheep (Knoess, 1976). Vitamin B₂ content in camel milk is also higher than in Afar goat milk, but the vitamin B₁ is lower in camel milk. Carotene concentrations in the milk declined from 0.46 mg/kg at 1.5 months lactation to 0.16 mg/kg at 4 months lactation (Bestuzheva, 1964). The vitamin A content has been reported as being as little as 0.037 mg percent (Kheraskov, 1961) to 1.264 mg/l (Anderson et al., 1940). Khan and Appona (1967) found an average of 7.57 ug/ml of vitamin A and 9.4 ug/ml of carotene. The latter used the method of sponification to extract the vitamin A and carotene.

The milk of all four quarters appears to have the same composition (Ohri and Joshi, 1961). Camel milk is very similar to goat milk and compares very favourably with human milk (Davis and McDonald, 1953). This again stresses the importance of camel milk for human nutrition. Camel herders living only on milk in Kenya (Fields, 1979) and in the Ahaggar region of the Sahara (Gast et al., 1969) are healthy and vigorous. Camel milk is renowned for its health-giving qualities, which includes good bone growth. Some camel herders living an camel milk only show a change in the colour of their hair to red (Gast et al., 1969), but this returns to normal when a more balance diet is resumed.

From all the data presented it is clear that the camel produces a nutritious milk for human consumption. It is also evident that the taste and quality of milk is directly affected by the amount of water drunk, and the amount and quality of feed eaten. The fluctuations in fat, protein, fat and salt are determined by the amount of water drunk (Yagil and Etzion, 1980) and by changes in pasture. Grazing on Atriplex halimus gives a salty taste to the milk, and grazing on Schouwia purpurea gives a cabbage smell to the milk (Gast et al., 1969).