Preliminary Study On The Basic Components And Molecular Basis Of Milk

Compared with the other domestic animals’ milk,donkey milk(DK)has the characteristics of low allergenic,low fat content,high lysozyme,etc.The composition of Donkey milk’s is similar to human milk and it is the best substitute for human milk.But the lactation of donkey is short and the production of milk is less than other domestic animals.There were little detailed reports about the the main ingredients of the donkey milk.For these reasons,the analysis of donkey milk’s nutrition and efficacy has a significance for the industrialized development of donkey milk.The preliminary testing and analysis of the main composition of Donkey milk.Chose N61 donkeys from 4 donkey farms for the experiment,using the milk composition analyzer Milko Scan?,FT+ and Somatic cell analyzer Fossomatic TM FC to test the donkey milk samples,the testing indexes including milk fat percentage,milk protein rate,lactose content,the number of somatic cells,lactose,urea nitrogen,etc.In the same time,analyzed the differences of the main composition of the donkey milk form the four farms and the reasons of the differences.It is found that the daily milk yield of Dezhou donkey is 0.25-1.22 kg/d,the average daily milk yield was0.91± 0.04 kg/d.There was no significant difference in daily milk yield between the four donkey farms(P > 0.05).The content of lactose in the donkey milk is4.96-7.07%;the average content of lactose was 6.55± 0.285%;the ratio of fat to proteinis 0.21± 0.009.And comparing the average fat percentage ratio of the four farms,the result showed the No.2 and No.3 farm is significantly higher than the No.1farm(P < 0.05).The somatic cell count was 12-48×103 cells/dl,and the average count in the four farms was not significantly different(P > 0.05).By detecting milk from the donkeys which suffering from mastitis,the number of somatic cells was 1172 ×103cells/dl,which was much higher than that of the healthy donkey milk(13.4±0.558×103 cells/dl).The results show that the number of somatic cells in donkey milk can also be used to diagnosis the mastitis of donkey.The average urea nitrogen content was 22.19± 0.965 mg/dl,which can be used to provide reference for thejudgment of the range of nitrogen content of donkey milk urea.The average urea nitrogen content in the No.2 donkey farm was 31.53± 1.371 mg/dl,which was significantly higher than that of the other three donkey farms(P < 0.01),which presumably related to high dietary protein content in No.2 donkey farm.Identification and quantitative analysis of Dezhou donkey milk proteins.According to the lactation period,8 donkey milk samples were divided into two groups: phase 1(days of lactation < 50 days)and phase 2(days of lactation > 50 days).According to the isotope labeling relative and absolute quantification(i TRAQ)and Mascot 2.3.02 software,a total of 401 donkey milk proteins were identified and quantified.There were 124 differential proteins between phase 2 and phase 1,22 of which were up-regulated and 102 were down-regulated.The gene ontology(GO)annotations showed that the proteins were mainly involved in the process of metabolism,biological regulation,immune response and growth and development which were located in cells,cell membranes and organelles,mainly play a role of connection and catalytic function.COG annotation results show that the identification of proteins were mainly involved in the metabolic process(Energy generation and metabolism(18),Carbohydrate transport and metabolism(15),Lipids transport and metabolism(10),Nucleic acids transport and metabolism(8),Amino acids transport and metabolism(10))and Modification,protein conversion,the function of molecular chaperone(54).The metabolic pathways showed that most of the donkey milk proteins were involved in Metabolic pathways(55),Complement and Coagulation cascade(31)and Immune and Inflammatory response relate to involved in Lysosomal pathway(26),Tuberculosis pathway(22)and Phagosome pathway(24).The analysis of Blast P software showed that the order of similarity between domestic animals’ milk and human milk protein sequences was: donkey milk > goat milk ≥ bovine milk > pig milk.The results of i BAQ showed that 265 proteins were given absolute abundance,including 14 up-regulated proteins and 48 down-regulated proteins.The main proteins in the donkey milk were β-lactoglobulin(LGB1),α-lactalbumin(LALBA)and lysozyme(LYZ).The bioinformatics analysis of the lysozyme protein showed that theLYSC1 gene and its high expression in the breast may be the reason of the lysozyme content in the donkey milk much higher than that of other mammals(human,cattle and sheep).Identification and quantitative analysis of metabolites of Dezhou donkey milk.According to the lactation period,30 donkey milk samples were divided into group 1(30-55 days),group 2(55-90 days),group 3(> 90 days).According to the usage of LC-MS/MS and Progenesis QI(Waters,U.K.)software,a total of 1685 first level identification numbers were identified in the positive ion mode,1182 first level identification numbers in the negative ion mode.There were 150 different metabolites between group 1 and group 2 and 73 different metabolites between group 2 and group3 have been found.The results of metabolic pathways showed that Fructose and Mannose metabolic pathways and Biosynthesis of amino acids,which were associated with the establishment of intestinal microflora.From what has been discussed above,the test of the main components of donkey milk not only reflects the quality of donkey milk,but also reacts of donkey’s milk production,health status,feeding and management level,etc.And the result of the test is also helpful for high-yield donkey’s orientation breeding.The analysis of donkey milk’s proteome and metabolomics not only expanded the knowledge of the donkey milk,but also proved that the donkey milk is much closer to human milk from the molecular level,in the same time reflects the donkey milk nutrition and medical value.This test would provide some technical support to the donkey milk industry.