共轭亚油酸对奶牛乳脂肪球粒径及分布的影响

旨在探索共轭亚油酸（CLA）对奶牛乳脂肪球粒径（MFG）及分布的影响。本试验选取24头体况相近的泌乳中期荷斯坦奶牛（体重（583±34.6）kg，产奶量（27.2±2.4）kg·d^-1），分为4组，每组6个重复，每个重复1头牛。对照组（C组）饲喂基础日粮，低剂量组（L组）饲喂基础日粮+150 g·d^-1 CLA，中剂量组（M组）饲喂基础日粮+300 g·d^-1 CLA，高剂量（H组）饲喂基础日粮+400 g·d^-1 CLA。连续饲喂5 d，测量奶牛采食量、产奶量和乳成分，采用Mastersizer 3000激光粒度仪测量乳脂肪球颗粒平均直径以及比例分布。结果发现，饲喂CLA对奶牛采食量、产奶量、乳蛋白和乳糖含量没有显著影响（P>0.05），CLA处理极显著降低了乳脂肪的含量（P<0.01）。与对照组相比，CLA处理组牛乳中脂肪球粒径D_3，2]和D_4，3]显著减少（P<0.05），并且随CLA添加剂量的增加，脂肪球分布比例呈现小脂肪球增多而大脂肪球减少的变化趋势。综上，在本试验条件下，饲粮CLA水平能够改变奶牛乳脂肪球粒径大小和比例，为阐明反式脂肪酸CLA造成奶牛低脂乳的内在机制提供基础。

Effect of Conjugated Linoleic Acid on the Size and Distribution of Milk Fat Globule in Dairy Cows

The aim of this study was to evaluate the effect of conjugated linoleic acid (CLA) on the size and distribution of milk fat globule(MFG) of dairy cows. Twenty-four Holstein cows with similar body condition in mid-lactation(body weight (583±34.6) kg，milk yield (27.2±2.4) kg·d^-1) were randomly assigned to 4 groups, 6 replicate in each group, and one cow in each replicate. The individuals in control group (C group) were fed with basal diet, the individuals in low dose CLA group (L group) were fed with basal diet + 150 g·d^-1 CLA, individuals in medium dose CLA group (M group) were fed with basal diet + 300 g·d^-1 CLA, individuals in high dose CLA group (H group) were fed with basal diet + 400 g·d^-1 CLA. Through 5 d treatment, dry matter intake(DMI) and milk yield were recorded and milk components were analyzed. The average diameter and particle size distribution of MFG were measured by Mastersizer 3000 laser particle size analyzer. The results showed that CLA supplement did not significantly affect the DMI, milk yield, content of milk protein and milk lactose(P>0.05), but extremely significantly reduced milk fat content (P<0.01). The mean particle size D_4,3]and D_3,2] of MFG in CLA group cows were significantly lower than those in the control group cows(P<0.05). Furthermore, CLA supplementation decreased the distribution percentage of large globule particles, and increased the distribution percentage of small globule particles. In this experiment, it can be concluded that dietary CLA levels affect size and distribution of MFG, which provides a basis for clarifying the mechanism of milk fat depression caused by CLA.