Xu Tianle, Tao Hui, Chang Guangjun, Zhang Kai, Xu Lei, Shen Xiangzhen
College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, 210095, China.
BMC Vet Res. 2015 Mar 7;11:52. doi: 10.1186/s12917-015-0360-6.
Dairy cows are often fed a high-concentrate diet to meet lactating demands, yet long-term concentrate feeding induces subacute ruminal acidosis (SARA) and leads to a decrease in milk fat. Stearoyl-CoA desaturase1 (SCD1) participates in fatty acid biosynthesis in the liver of lactating ruminants. Here, we conducted this study to investigate the impact of lipopolysaccharide derived from the rumen on SCD1 expression and on fatty acid composition in the liver of dairy cows fed a high-concentrate diet. Eight multiparous mid-lactating Holstein cows (455 ± 28 kg) were randomly assigned into two groups in the experiment and were fed a low-concentrate diet (LC) or high-concentrate diet (HC) for 18 weeks.
The results showed that the total volatile fatty acids and lactic acid accumulated in the rumen, leading to a decreased rumen pH and elevated lipopolysaccharides (LPSs) in the HC group. The long chain fatty acid profile in the rumen and hepatic vein was remarkably altered in the animals fed the HC diet. The triglyceride (TG), non-esterified fatty acid (NEFA) and total cholesterol (TCH) content in the plasma was significantly decreased, whereas plasma glucose and insulin levels were increased. The expression of SCD1 in the liver was significantly down-regulated in the HC group. In regards to transcriptional regulators, the expression of sterol regulatory element binding transcription factors (SREBF1c, SREBF2) and SREBP cleavage activating protein (SCAP) was down-regulated, while peroxisome proliferator-activated receptor α (PPARα) was up-regulated.
These data indicate that lipopolysaccharide derived from the rumen down-regulates stearoyl-CoA desaturase 1 expression and alters fatty acid composition in the liver of dairy cows fed a high-concentrate diet.
为满足泌乳需求，奶牛常被饲喂高浓度日粮，但长期饲喂高浓度日粮会引发亚急性瘤胃酸中毒（SARA），并导致乳脂率下降。硬脂酰辅酶A去饱和酶1（SCD1）参与泌乳反刍动物肝脏中的脂肪酸生物合成。在此，我们开展本研究，以探究瘤胃来源的脂多糖对饲喂高浓度日粮奶牛肝脏中SCD1表达及脂肪酸组成的影响。实验中，8头经产中期泌乳的荷斯坦奶牛（体重455±28千克）被随机分为两组，分别饲喂低浓度日粮（LC）或高浓度日粮（HC），为期18周。
结果显示，HC组瘤胃中总挥发性脂肪酸和乳酸积累，导致瘤胃pH值降低，脂多糖（LPS）水平升高。饲喂HC日粮的动物瘤胃和肝静脉中的长链脂肪酸谱发生显著改变。血浆中甘油三酯（TG）、非酯化脂肪酸（NEFA）和总胆固醇（TCH）含量显著降低，而血浆葡萄糖和胰岛素水平升高。HC组肝脏中SCD1的表达显著下调。在转录调节因子方面，固醇调节元件结合转录因子（SREBF1c、SREBF2）和SREBP裂解激活蛋白（SCAP）的表达下调，而过氧化物酶体增殖物激活受体α（PPARα）上调。
这些数据表明，瘤胃来源的脂多糖下调了饲喂高浓度日粮奶牛肝脏中硬脂酰辅酶A去饱和酶1的表达，并改变了脂肪酸组成。
