Murrieta C M, Hess B W, Scholljegerdes E J, Engle T E, Hossner K L, Moss G E, Rule D C
Department of Animal Science, University of Wyoming, Laramie, Wyoming 82071, USA.
J Anim Sci. 2006 Sep;84(9):2399-405. doi: 10.2527/jas.2005-677.
Our objectives were 2-fold: to determine the effect of dietary linoleate on milk fat composition and on transcript abundance of acetyl-CoA carboxylase (ACC), fatty acid synthase (FAS), lipoprotein lipase (LPL), and stearoyl-CoA desaturase (SCD) mRNA in mammary tissue, and to evaluate milk somatic cell mRNA as a source of mammary tissue mRNA for these enzymes. Eighteen primiparous, crossbred beef cows (BW = 411 +/- 24 kg; BCS = 5.25) were offered Foxtail millet hay at 1.68% of BW daily and either a low-fat control (n = 9) or a high-linoleate (79% 18:2n-6), cracked safflower seed supplement (n = 9). Diets were isonitrogenous and isocaloric, and the linoleate diet contained 5.4% of DMI as fat. At slaughter (37 +/- 3 d postpartum), mammary tissue was sampled and immediately frozen in liquid N2 before being stored at -80 degrees C. Milk samples were obtained from the same mammary glands and immediately centrifuged at 1,200 x g to pellet somatic cells. A ribonuclease protection assay was used to quantify the mRNA in the mammary gland and milk somatic cells. Effects of diet, tissue, or their interaction were not observed for ACC (P = 0.28, 0.89, and 0.35, respectively), FAS (P = 0.38, 0.66, and 0.20, respectively), LPL (P = 0.09, 0.15, and 0.43, respectively), or SCD (P = 0.45, 0.19, and 0.29, respectively). Dietary effects on fatty acid profile of the milk fat suggested that linoleate supplementation might have decreased de novo lipogenesis while increasing uptake of dietary fatty acids; this effect was consistent with a trend toward greater LPL mRNA for linoleate-fed cows (P = 0.09). Correlations (r values) between mammary tissue and milk somatic cell data for each mRNA for the low-fat control diet were: ACC, 0.76 (P = 0.02); FAS, 0.69 (P = 0.04); LPL, 0.68 (P = 0.04); and SCD, 0.73 (P = 0.05), and for the linoleate diet were: ACC, 0.85 (P = 0.003); FAS, 0.75 (P = 0.02); LPL, 0.90 (P = 0.001); and SCD, 0.73 (P = 0.03). We conclude that milk somatic cells obtained from lactating beef cows can be used as a source of RNA to study nutritional regulation of mammary gland lipogenesis in cows fed dietary fat supplements.
一是确定日粮亚油酸对乳脂肪组成以及乳腺组织中乙酰辅酶A羧化酶（ACC）、脂肪酸合酶（FAS）、脂蛋白脂肪酶（LPL）和硬脂酰辅酶A去饱和酶（SCD）mRNA转录丰度的影响；二是评估乳体细胞mRNA作为这些酶的乳腺组织mRNA来源的情况。18头初产杂交肉牛（体重=411±24千克；体况评分=5.25），每天按体重的1.68%饲喂粟谷干草，并分别给予低脂对照日粮（n=9）或高亚油酸（79% 18:2n-6）的破碎红花籽补充料（n=9）。日粮蛋白质和能量含量相同，亚油酸日粮的脂肪含量占干物质采食量的5.4%。在屠宰时（产后37±3天），采集乳腺组织并立即在液氮中冷冻，然后储存在-80℃。从同一乳腺采集乳样，并立即以1200×g离心以使体细胞沉淀。采用核糖核酸酶保护分析法对乳腺和乳体细胞中的mRNA进行定量。对于ACC（分别为P=0.28、0.89和0.35）、FAS（分别为P=0.38、0.66和0.20）、LPL（分别为P=0.09、0.15和0.43）或SCD（分别为P=0.45、0.19和0.29），未观察到日粮、组织或它们之间相互作用的影响。日粮对乳脂肪脂肪酸谱的影响表明，补充亚油酸可能减少了脂肪酸从头合成，同时增加了日粮脂肪酸的摄取；这种影响与饲喂亚油酸的奶牛LPL mRNA有增加趋势一致（P=0.09）。低脂对照日粮中每种mRNA的乳腺组织和乳体细胞数据之间的相关性（r值）为：ACC，0.76（P=0.02）；FAS，0.69（P=0.04）；LPL，0.68（P=0.04）；SCD，0.73（P=0.05），亚油酸日粮的相关性为：ACC，0.85（P=0.003）；FAS，0.75（P=0.02）；LPL，0.90（P=0.001）；SCD，0.73（P=0.03）。我们得出结论，从泌乳肉牛获得的乳体细胞可作为RNA来源，用于研究饲喂日粮脂肪补充料的奶牛乳腺脂肪生成的营养调控。
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