ETH Zurich, Institute of Plant, Animal and Agroecosystem Sciences, Universitaetstrasse 2, CH-8092 Zurich, Switzerland.
J Dairy Res. 2010 Aug;77(3):331-6. doi: 10.1017/S0022029910000257. Epub 2010 May 19.
The transfer of ingested alpha-linolenic acid (ALA) and linoleic acid (LA) determines the nutritional quality of milk, but the factors determining this transfer are unclear. The present experiment investigated the influence of roughage to concentrate proportions and the effect of concentrate types on milk fat composition. Respectively, six lactating dairy cows were fed one of three isoenergetic (5.4+/-0.05 MJ net energy for lactation/kg dry matter; DM) and isonitrogenous (215+/-3.5 g crude protein/kg DM) diets, consisting of ryegrass hay only (33 g fatty acids/kg DM; ALA-rich, no concentrate), maize (straw, whole maize pellets and gluten; 36 g fatty acids/kg DM; LA-rich; 560 g concentrate/kg DM), or barley (straw and grain plus soybean meal; 19 g fatty acids/kg DM; LA-rich; 540 g concentrate/kg DM). The fatty acid composition of feeds and resulting milk fat were determined by gas chromatography. The ALA concentration in milk fat was highest (P<0.001) with the hay-diet, but the proportionate transfer of ALA from diet to milk was lower (P<0.001) than with the maize- or barley-diets. The LA concentration in milk fat was highest with the maize-diet (P<0.05, compared with hay) but relative transfer rate was lower (P=0.01). The transfer rates of ALA and LA were reciprocal to the intake of individual fatty acids which thus contributed more to milk fat composition than did roughage to concentrate proportions. The amount of trans-11 18:1 in milk fat was lowest with the barley-diet (P<0.001) and depended on the sum of ALA and LA consumed. The milk fat concentration of cis-9, trans-11 18:2 (rumenic acid) was more effectively promoted by increasing dietary LA (maize) than ALA (hay). Amounts of 18:0 secreted in milk were four (maize) to seven (hay) times higher than the amounts ingested. This was suggestive of a partial inhibition of biohydrogenation in the maize-diet, possibly caused by the high dietary LA level.
摄入的α-亚麻酸（ALA）和亚油酸（LA）的转移决定了牛奶的营养价值，但决定这种转移的因素尚不清楚。本实验研究了粗饲料与精饲料比例以及精饲料类型对乳脂组成的影响。分别给 6 头泌乳奶牛饲喂三种等能量（5.4+/-0.05 MJ 泌乳净能/千克干物质；DM）和等氮（215+/-3.5 g 粗蛋白/千克 DM）的日粮，日粮分别由黑麦干草（33 g 脂肪酸/千克 DM；富含 ALA，无精饲料）、玉米（秸秆、全玉米颗粒和玉米蛋白粉；36 g 脂肪酸/千克 DM；富含 LA；560 g 精饲料/千克 DM）或大麦（秸秆和谷物加豆粕；19 g 脂肪酸/千克 DM；富含 LA；540 g 精饲料/千克 DM）组成。通过气相色谱法测定饲料和乳脂中的脂肪酸组成。乳脂中的 ALA 浓度最高（P<0.001），但日粮中 ALA 的比例转移率较低（P<0.001），低于玉米或大麦日粮。玉米日粮中乳脂中的 LA 浓度最高（P<0.05，与黑麦日粮相比），但相对转移率较低（P=0.01）。ALA 和 LA 的转移率与单种脂肪酸的摄入量成反比，因此，与粗饲料与精饲料的比例相比，脂肪酸的摄入量对乳脂组成的影响更大。大麦日粮中乳脂中的反式-11 18:1 含量最低（P<0.001），并且取决于所摄入的 ALA 和 LA 的总和。乳脂中环式 9，反式-11 18:2（瘤胃酸）的浓度通过增加日粮中的 LA（玉米）比 ALA（黑麦）更有效地促进。在乳中分泌的 18:0 数量是摄入数量的 4（玉米）到 7（黑麦）倍。这表明在玉米日粮中存在生物氢化的部分抑制，可能是由于日粮中 LA 水平较高所致。
