Changes in chemical composition of Alxa bactrian camel milk during lactation

Changes in chemical composition of Alxa bactrian camels reared in Inner Mongolia ( China) during lactation were investigated. Colostrum and milk samples from 10 nomadic female camels in their first season of lactation were collected periodically from parturition until 90 d postpartum ( PP). The average contents of gross composition were 14.23% protein, 4.44% lactose, 0.27% fat, 0.77% ash, and 20.16% total solids in colostrum at 2 h PP, and the respective mean values were 3.55, 4.24, 5.65, 0.87, and 14.31% for regular milk on d 90. A 15- fold increase was shown in fat content during the first 24 h, whereas a sharp decrease was shown during the first 12 h of lactation in protein, ash, and total solids contents. Variation in lactose content was small ( 4.24 to 4.71%) throughout the study period. Total N, nonprotein N, casein N, and whey protein N were found to be 2.23, 0.06, 0.86, and 1.31 g/ 100 mL for the colostrum at 2 h PP; and 0.56, 0.04, 0.45, and 0.07 g/ 100 mL for the milk at 90 d PP. Percentages of caseins increased steadily, whereas whey proteins declined gradually until 3mo of lactation. Gas liquid chromatography analysis of milk fat showed that the content of even- numbered saturated fatty acids ( C-12:0-C-18:0) in camel colostrum ( 2 h to 7 d PP) was lower than that of regular milk ( 15 to 90 d PP). The predominant saturated fatty acids were C-14:0, C-16:0, and C-18:0, regardless of the stage of lactation. There was a considerable level of polyunsaturated fatty acids ( mainly C-18:1) in Alxa camel's milk fat. The levels of Ca, P, Na, K, and Cl were 222.58, 153.74, 65.0, 136.5, and 141.1 mg/ 100 g, respectively, at 2 h PP; the values of the minerals were 154.57, 116.82, 72.0, 191.0, and 152.0 mg/ 100 g, respectively, for the regular milk on d 90. The levels of vitamins A, C, E, B-1, B-2, B-6, and D were 0.97, 29.60, 1.45, 0.12, 1.24, 0.54 mg/ L, and 640 IU/ L, respectively, in Alxa camel milk at 90 d PP. Vitamin A and C contents were higher and vitamins E and B-1 were lower than those in colostrum. Sodium dodecyl sulfate- PAGE and densitometry results demonstrated that Alxa camel colostrum is rich in immunoglobulins, serum albumin, and 2 unknown fractions, which are reduced in amount (%) within 2 d of lactation. It seems that there is lack of beta- lactoglobulin in Alxa camel milk, whereas casein and alpha- lactalbumin start at a low level and increase gradually until they reach their regular levels in the milk.