Kelsey J A, Corl B A, Collier R J, Bauman D E
Department of Animal Science, Cornell University, Ithaca, NY 14853, USA.
J Dairy Sci. 2003 Aug;86(8):2588-97. doi: 10.3168/jds.S0022-0302(03)73854-5.
Dairy products are the main source of conjugated linoleic acid (CLA), a functional food component with health benefits. The major source of cis-9, trans-11 CLA in milk fat is endogenous synthesis via delta9-desaturase from trans-11 18:1, with the remainder from incomplete rumen biohydrogenation of linoleic acid. Diet has a major influence on milk fat CLA; however, effects of physiological factors have received little attention. Our objectives were to examine milk fat content of CLA and the CLA-desaturase index with regard to: 1) effect of breed, parity, and stage of lactation, and 2) variation among individuals and the relationship to milk and milk fat. Holstein (n = 113) and Brown Swiss (n = 106) cows were fed a single diet and milk sampled on the same day to avoid confounding effects of diet and season. Frequency distributions demonstrated that milk fat content of CLA and CLA-desaturase index varied over threefold among individuals, and this needs to be considered in the design of experiments. Holsteins had a higher milk fat content of CLA and CLA-desaturase index, but breed differences were minor. Parity and days in milk also had little or no relationship to the individual variation for these two CLA variables. Breed, parity, and days in milk accounted for < 0.1, < 0.3, and < 2.0% of total variation in CLA concentration in milk fat, respectively. Milk fat content of CLA and CLA-desaturase index were essentially independent of milk yield, milk fat percent, and milk fat yield. We speculate that the basis for the genetic variation among individuals is related to rumen output of trans-11 18:1 and to a lesser extent cis-9, trans-11 CLA, and to the tissue amount and activity of delta9-desaturase.
乳制品是共轭亚油酸（CLA）的主要来源，CLA是一种具有健康益处的功能性食品成分。乳脂肪中顺-9，反-11 CLA的主要来源是通过δ9-去饱和酶将反-11 18:1进行内源性合成，其余部分来自亚油酸在瘤胃中不完全的生物氢化作用。饮食对乳脂肪CLA有重大影响；然而，生理因素的影响却很少受到关注。我们的目标是研究CLA的乳脂肪含量和CLA-去饱和酶指数，具体涉及：1）品种、胎次和泌乳阶段的影响，以及2）个体间的差异及其与牛奶和乳脂肪的关系。给荷斯坦奶牛（n = 113）和瑞士褐牛（n = 106）饲喂单一日粮，并在同一天采集牛奶样本，以避免日粮和季节的混杂影响。频率分布表明，个体间CLA的乳脂肪含量和CLA-去饱和酶指数变化超过三倍，这在实验设计中需要考虑。荷斯坦奶牛的CLA乳脂肪含量和CLA-去饱和酶指数较高，但品种差异较小。胎次和泌乳天数与这两个CLA变量的个体差异也几乎没有关系。品种因素、胎次因素和泌乳天数分别仅占乳脂肪中CLA浓度总变异的<0.1%、<0.3%和<2.0%。CLA的乳脂肪含量和CLA-去饱和酶指数基本上与产奶量、乳脂肪百分比和乳脂肪产量无关。我们推测，个体间遗传变异的基础与反-11 18:1的瘤胃输出有关，在较小程度上与顺-9，反-11 CLA有关，还与δ9-去饱和酶的组织含量和活性有关。
