Study On Effects Of Different Diets On Milk Protein Synthesis In The Mammary Gland Of Dairy Cows

Low milk protein content is the issue for producers in China, so based on the feedresources of China, formulate diets is of practical significance as a means to improvemilk protein production.This study was to evaluate the effects of three diets on the milkprotein synthesis in mammary gand of dairy cows, and those diets is very representativeof feeding for dairy cows in China. Identify key factors that may affect the milk proteinsynthesis, and to provide scientific data in order to increase the level of milk production,promote the development of dairy industry.Experiment1: Study on the effects of Different Amino Acid Pattern on caseinsynthesis in Primary Cultured Bovine Mammary Epithelial CellsA completely random design was used. Four AA patterns reatments are as follows:blood AA pattern in low protein diet (LPBP); milk protein AA pattern (MP);80%caseinplus20%lactoalbumin AA pattern (CLP); casein AA pattern (CP). Each treatment hasthree replicates, and all experiments were repeated three times. The expression ofCSN1S1, CSN3, GLUT1, PRLR, STAT5, mTOR genes and the content of αS-casein weredetermined by RT-QPCR method and αS-casein ELISA Kit, respectively.Cellproliferation was determined by CCK-8method.The results showed that: The milkprotein AA pattern might increase major milk protein genes expression. Perhaps, anappropriate AA pattern can promote mTOR STAT5PRLR GLUT1genes expression, andresult in increased milk protein synthesis. In addition, the level of geng expression trendwas different from the proliferation in mammary gland epithelial cell.Experiment2：The effects of Different diets on milk production and milkcomposition of dairy cowsThe second part was mainly conducted to study the effects of three diets on milkproduction and milk composition of dairy cows, and provide the data to the research ofmilk protein synthesis in the mammany gland. Thirty multiparous Holstein cows wereassigned to a single factor block design and cows were divided into three groups.Threediets were:1）Mixed forage represent Large-scale dairy farming.2) High-concentrate andcorn stover represent dairy farming.3) Low-concentrate and corn stover represent retaildairy farming.The exprement period were12weeks, and pre-feeding period were3weeks, every3weeks for a test cycle.Feed and milk sample were collected at15～18d ineach cycle.The results showed that: The MF group had a best performance, there was no difference between CSA and MF in milk protein yield and milk proten content, however,the Lactation efficiency was higher in MF vs.CSA. Compared to the CSA and MF, CSBhad lower level of all indicators of milk composition except milk fat. The results suggestthat, blance diets more efficient in nutrients metabolism, the energy level of CSB can notmaintain the lactating.Experiment3: The effects of Different diets on metabolin content related to milkprotein synthesis in artery/vein blood of dairy cowsBased on experiment2, the objective of this part was to evaluate the metabolincontent related to milk protein synthesis in artery/vein blood of dairy cows and found outthe key factor that affect milk protein synthesis.The results showed that:PRL,GH,INR,IGF-1and glouse content in artery/vein blood have no difference indifferent diets(P>0.05), the level of BUN and leptin in EPA were higher in CSAvs.CSB and MF significantly, compare to the MF, CSA and CSB were significant higherin AST. Most of the amino acids have no difference in different diets, but, the ratio ofAsp, Arg, Thr, His, Gly and Leu have significant difference or difference in the trend.The results suggest that, CSA and CSB have low efficiency of nitrogen utilization. Leptinmay affect the synthesis of milk fat in the CSA group. The health of the liver wasaffented by CSA and CSB, perhaps.Experiment4: The effects of Different diets on AA uptake and utilization inmamany gland of dairy cowsBased on experiment2, the objective of this part was to evaluate the difference ofAA uptake and utilization in mammary gland.The results showed that: the AA utilizationof mammary gland of CSB was restricted by the level of EAA in EPA, the reason was thelow level of nutrition and blood flow. There was no difference in AA uptake andutilization between CSA and MF.Experiment5: Effects of different diets on the Gene Expression Related to MilkProtein Synthesis in the Mammary Gland of dairy cowsBased on experiment2, Mammary gland tissue (ca.500mg/animal) for RNAextraction were randomly performed for half numbers of cows in each group aftermilking on the last day of experiment. The expression of CSN1S1, CSN1S2,CSN3,INSR,PRLR, GHR1A, JAK2，STAT5and mTOR genes were determined by RT-QPCR method.The results showed that: Different diets affected the efficiency of milk protein synthesisin lactating Holstein cows. The balance dites can promote PRLR GHR1A and mTORgenes expression, resulting in increased milk protein synthesis. The final results showed that: AA supply and utilization efficiency in mammarygland result in different milk protein and yield, milk protein synthesis efficiency wasevaluated by the gene expression related to milk protein synthesis in the mammary glandtissue. The milk protein AA pattern might increase major milk protein genes expression.Perhaps, the milk protein pattern can promote milk protein synthesis in mammary glandepithelial cell better.