Vahmani P, Glover K E, Fredeen A H
Department of Biology, Dalhousie University, Halifax, Nova Scotia B3H 4J1, Canada.
Azar Agriculture, Truro, Nova Scotia B2N 5Z3, Canada.
J Dairy Sci. 2014 Jul;97(7):4174-83. doi: 10.3168/jds.2013-7290. Epub 2014 May 2.
Research was conducted to evaluate the effects of management system (MS), marine lipid supplementation (LS), and their interaction on the relative mRNA abundance of 11 genes involved in lipid synthesis in mammary, liver, and subcutaneous adipose tissues in lactating dairy cows. These genes included those involved in FA uptake (LPL), de novo FA synthesis (ACACA, FASN), FA desaturation (SCD1, FADS1, FADS2), and transcriptional regulation of lipogenesis (SREBF1, SCAP, INSIG1, THRSP, and PPARG). Forty-eight peripartal Holstein cows were blocked by parity and predicted calving date and assigned to either a pasture (n=23) or confinement (n=25) system. Within each system, cows were allocated randomly (7-9 cows per treatment) to a control (no oil supplement) or 1 of 2 isolipidic (200 g/d) supplements, fish oil (FO) or microalgae (MA), for 125 ± 5 d starting 30 d precalving. The experiment was conducted as a split-plot design, with MS being the whole plot treatment and LS as the subplot treatment. At 100 ± 2 DIM, 4 cows from each treatment combination (24 cows in total) were euthanized and tissue samples were collected for gene expression analysis. No interactions between MS and LS were observed regarding any of the variables measured in this study. Milk production (34.0 vs. 40.1 kg/d), milk fat (1.10 vs. 1.41 kg/d), protein (0.95 vs. 1.22 kg/d), and lactose (1.56 vs. 1.86 kg/d) were lower for pasture compared with confinement. The effect of LS on milk production and milk composition (yields and contents) was significant only for milk fat content that was reduced with MA compared with FO (3.00 vs. 3.40%) and the control (3.56%). The mammary mRNA abundance of PPARG (-32%) and FASN (-29%) was lower in grazing compared with confined cows, which was accompanied by reduced (-43%) secretion of de novo synthesized fatty acids in milk. Grazing was associated with reduced expression of ACACA (-48%), FASN (-48%), and THRSP (-53%) in subcutaneous adipose tissues, which was consistent with the lower body condition score (i.e., lower net adipose tissue deposition) in grazing compared with confined cows. Feeding either FO or MA downregulated hepatic expression of FASN, SCD1, FADS2, and THRSP. The reduced secretion of de novo synthesized fatty acids in milk of grazing cows compared with confined cows might be related in part to the downregulation of genes involved in lipid synthesis, and that LS have tissue-specific effects on expression of genes involved in lipid metabolism, with liver being the most responsive tissue.
开展了一项研究，以评估管理系统（MS）、海洋脂质补充剂（LS）及其相互作用对泌乳奶牛乳腺、肝脏和皮下脂肪组织中11个参与脂质合成的基因的相对mRNA丰度的影响。这些基因包括参与脂肪酸摄取（LPL）、从头脂肪酸合成（ACACA、FASN）、脂肪酸去饱和（SCD1、FADS1、FADS2）以及脂肪生成转录调控（SREBF1、SCAP、INSIG1、THRSP和PPARG）的基因。48头围产期荷斯坦奶牛按胎次和预测产犊日期进行分组，并分配到牧场（n = 23）或圈养（n = 25）系统。在每个系统内，奶牛被随机分配（每个处理7 - 9头奶牛）至对照组（不补充油脂）或两种等脂（200 g/d）补充剂中的一种，即鱼油（FO）或微藻（MA），从产犊前30天开始持续125±5天。实验采用裂区设计，MS为全区处理，LS为副区处理。在产犊后100±2天，对每个处理组合中的4头奶牛（共24头奶牛）实施安乐死，并采集组织样本进行基因表达分析。在本研究中测量的任何变量方面，均未观察到MS和LS之间的相互作用。与圈养相比，牧场饲养的奶牛产奶量（34.0对40.1 kg/d）、乳脂（1.10对1.41 kg/d）、蛋白质（0.95对1.22 kg/d）和乳糖（1.56对1.86 kg/d）较低。LS对产奶量和乳成分（产量和含量）的影响仅对乳脂含量显著，与FO（3.00%对3.40%）和对照组（3.56%）相比，MA组的乳脂含量降低。与圈养奶牛相比，放牧奶牛乳腺中PPARG（-32%）和FASN（-29%）的mRNA丰度较低，同时乳中从头合成脂肪酸的分泌减少（-43%）。放牧与皮下脂肪组织中ACACA（-48%）、FASN（-48%）和THRSP（-53%）的表达降低有关，这与放牧奶牛相比圈养奶牛较低的体况评分（即较低的净脂肪组织沉积）一致。饲喂FO或MA均可下调肝脏中FASN、SCD1、FADS2和THRSP的表达。与圈养奶牛相比，放牧奶牛乳中从头合成脂肪酸分泌减少可能部分与脂质合成相关基因的下调有关，并且LS对参与脂质代谢的基因表达具有组织特异性影响，其中肝脏是最敏感的组织。
