植物油来源亚油酸和亚麻酸对乳脂CLA合成的影响

Effect of Linoleic and Linolenic Acid on Milk Fat Conjugated Linoleic Acid from Dairy Cows

选用40头泌乳中期(169.8±8)DIM的中国荷斯坦奶牛随机分为4组,采用完全随机试验设计,研究日粮亚油酸和亚麻酸水平对乳脂CLA合成的影响。试验共设4个处理,分别为高亚油酸组(LA)、高亚麻酸组(LEA)、高亚油酸和亚麻酸组合组(HLALEA)和低亚油酸和亚麻酸组(LLALEA)。通过9周的试验结果表明,不同处理对干物质采食量、泌乳净能校正产奶量、乳蛋白及乳脂肪的含量和日产量均没有显著影响。增加日粮中LA或LEA的含量,能够显著降低乳脂C12∶0、C14∶0和C16∶0的含量(P<0.05),显著增加乳中硬脂酸(C18∶0,P<0.05)和18碳长链不饱和脂肪酸的含量(P<0.01),但对20碳以上不饱和脂肪酸的影响小(P>0.05)。随着日粮中亚油酸含量的增加,LLALEA、HLEA、HLALEA和HLA组乳脂TVA和c9t11CLA的含量呈线性增加。HLEA组、HLALEA和HLA组乳脂TVA的含量分别比LLALEA组增加1.56、3.05和4.71 g/100 g,而c9t11CLA分别比LLALEA组提高2.5、2.8和3.7倍。因此表明,日粮亚油酸对乳脂c9t11CLA合成的贡献效果高于亚麻酸,而亚油酸调控乳脂CLA合成机制主要以提供乳腺SCD合成c9t11CLA所需的底物(TVA)为主。

Objective of this study was to determine the comparative effectiveness of linoleic and linolenic acid in enhancing CLA in milk when fed at the same levels to mid lactation dairy cows. Forty dairy cows were randomly assigned to 4 treatments. Cows in four treatments were fed a basal diet that was supplemented oils differed in their linoleic and linolenic acid contents. The four treatments were Low linoleic and linolenic acid（LLALEA）, high linoleic（HLA）, High linolenic acid（HLEA） or High linoleic and linolenic acid（HLALEA）. Experimental duration was 9 weeks and measurements were made during the last 6 weeks. Dry matter intake, energy corrected milk （ECM） , milk fat and protein contents were not differ among treatments. The proportions of C18 ： 1 trans-11 （TVA） and C18 ： 2 cis-9, trans-11 （CLA） were 1.48, 6.19, 3.04, and 4.53 （P=0.01）, 0.64, 2.39, 1.60, and 1.81% of total fatty acid methyl esters in LLALEA, HLA, HLEA, and HLALEA, respectively. The proportions of unsaturated fatty acids were 27.9, 33. 6, 36.4, and 33.8 （P=0.001） in LLALEA, HLA, HLEA, and HLALEA, respectively. Feeding free oil rich in linoleic acid is 100 and 50% more effective in enhancing TVA and CLA in milk fat, respectively, than feeding free oil rich in linolenic acid fed at the similar levels in the diet.The milk fat content of CLA c-9,t11 across the whole treatment increased linearly with increased intake of dietary LA. Milk fat concentration of TVA in HLEA,HLALEA and HLA were 1.56, 3.05 and 4.71 g/100 g higher than LLALEA respectively ,while CLA c-9,t11 were 2.5,2.8 and 3.7 times respectively. Therefore, dietary LA , which was used as the main substrate for CLA endogenous synthesis via SCD in the mammary gland, is more effective than LEA in enhancing milk CLA c-9, t11 concentration.