Fatty Acids Changes Of Milk And Transcriptional Regulation Analysis Of Mammary Gland Tissue In The Early Milk Of Dairy Cows

In this study,the changes in the proportion of fatty acids in milk were determined by using Chinese Holstein dairy cows.Combined with transcriptome sequencing techniques and bioinformatics methods,Transcription of Lipid Metabolism Process,such as FA import into cells,Denovo synthesis,Xenobiotic and Cholesterol transport,Acetate and FA activation and intra-cellular transport,Fatty acid synthesis and desaturation,Lipid droplet formation and secretion,and Post-transcriptional regulatory mechanisms in early lactation of the mammary gland tissue were researched.According to the results of transcriptome sequencing,genes differentially expressed in early lactation were screened.These genes clarified the lipid synthesis and metabolic mechanism of mammary gland,achieved the directional control of milk composition,and laid the foundation for the production of high quality raw milk.In the experimental,33 healthy Holstein dairy cows selected from Yangzhou University Experimental Farm Ranch farmland of Yangzhou University were divided into two groups,one group of 30(2-3 fetuses)were used for the determination of milk composition in milk,the other group of 3(2-3 fetuses)were used for the collection of breast tissue.During the study period,the cows from the two groups were fed with TMR diets and the management conditions remained consistent.The percentage content of milk fat percentage,milk protein,lactose,non-fat milk solids and fatty acids in milk were determined by using the milk which was collected at 3,30,90 days of the 33 cows.The mammary gland tissue of the second group of dairy cows was collected at the-7th,30th,90th days with minimally invasive method,and were performed a deep transcriptome sequence with RNA-seq high-throughput sequencing.The main results are as follows:1.41 kinds of fatty acids in milk were detected by gas chromatography,18 kinds of fatty acids(C4:0?C6:0?C8:0?C10:0?C12:0?C14:0?C15:0?C16:0?C16:1,cis-9?C18:0?C18:1,cis-9?C18:2,cis-9,12?SFA?MUFA?PUFA?sc-FA?mc-FA and lc-FA)which had a percentage content of more than 1%and significant differences were analyzed.The results showed that the content of the other 17 kinds of fatty acids had significant difference at 3 d and 30 d apart from C16:1,cis-9(P<0.05),the content of the other 15 kinds of fatty acids had no significant difference at 30 d and 90 d apart from C4:0?C6:0 and sc-FA(P>0.05),the content of 16 kinds of fatty acids had significant difference at 3 d and 90 d apart from C4:0 and sc-FA(P<0.05).2.Using RNA-seq to analysis the mammary gland tissue of different period.New transcripts predicted that 8706 new transcripts in mammary gland tissue at different times,with 3253 transcripts had coding ability.Known gene structure optimization results showed that 1664 known gene structure were optimized in mammary gland tissue of different periods and the optimization were major performed in the sequence extension of the gene starting position to the termination position.The results showed that 2421 siginficantly differentially expressed genes were screened from mammary gland tissue of-7 d and 30 d;33 siginficantly differentially expressed genes were screened from mammary gland tissue of 30 d and 90 d.3.Pathway analysis of these differentially expressed genes sceened out a total 15 significant pathway:PPAR signaling pathway,Glycerol and lipid metabolism signaling pathway,Fatty acid metabolism signaling pathway and Biosynthesis of unsaturated fatty acids signaling pathway,etc.4.A significant analysis of 30 genes associated with fatty acid synthesis metabolism in pathways was performed.The results showed that CD36,ABCA1,SLC27A6,ACSL1,ACSS1,ACSS2,FASN,AGPAT6,DGAT2,GPAM,GPAT2,LPIN1 and SOCS3 genes were significantly different during lactation initiation(P<0.05),SOCS3,FABP4,GPAT2,DGAT1 and DGAT2 genes were significantly different during lactation initiation.The correlation analysis between these genes and the fatty acid composition of dairy cows was performed.The results demonstrated that other genes were significantly or extremely significantly associated with one or more kinds of the fatty acids except for FADS2,GPAT2.To conclusion,these genes were directly or indirectly involved in the process of fatty acid metabolism.The study found that CD36,ABCA1,SLC27A6,ACSL1,ACSS1,ACSS2,FASN,AGPAT6,DGAT2,GPAM,GPAT2,LPIN1 and SOCS3 genes played an important role in the initiation and maintenance process of lactation.Genes screened from signals pathway associated with fatty acid metabolism,such as PPAR signaling pathway,Glycerolipid metabolism signaling pathway,Fatty acid metabolism signaling pathway,and Biosynthesis of unsaturated fatty acids signaling pathway,could be used as a candidate gene group for the deep study on the lactation mechanism of mammary gland.