真胃灌注葡萄糖对泌乳奶山羊乳脂合成的影响

Effects of Abomasal Glucose Infusion on Milk Fat Synthesis in Lactating Goats

旨在研究血糖/胰岛素水平升高是否是高精料日粮抑制乳脂合成的途径,及其抑制的机制。采用4只泌乳早期崂山奶山羊,安装真胃插管和颈动脉插管。2×2有重复交叉试验设计,2个试验处理为真胃灌注生理盐水或200g·d-1葡萄糖。2期试验,每期8d,2期之间间隔14d。使用RT-PCR检测乳脂合成相关酶的mRNA表达量。结果表明,真胃灌注葡萄糖显著提高了血糖水平(P<0.05),血浆胰岛素水平有升高趋势(P=0.06)。葡萄糖灌注提高了产奶量(P<0.05),降低了乳脂率和乳脂量(P<0.05)。乳脂中,C18∶0和C9C18∶1的产量显著降低(P<0.05),从头合成的脂肪酸(C4~C14)及血液吸收和从头合成双重来源脂肪酸(C16)的产量无显著变化(P>0.05)。真胃灌注葡萄糖对乙酰辅酶A羧化酶、脂肪合成酶、脂蛋白酯酶、脂肪酸结合蛋白、磷酸甘油酰基转移酶、脂肪酸脱饱和酶等乳脂合成酶和脂肪酸转运蛋白基因的表达无显著影响。结论:真胃灌注葡萄糖主要通过减少血液来源脂肪酸含量来降低乳脂产量;其对乳脂合成相关酶及蛋白基因表达无影响,对乳脂合成的调控发生在转录后。

The aims of the present study were to investigate if high concentrate diets with high concentration blood glucose and insulin depress milk fat synthesis and the underlying mechanism.4Laoshan dairy goats in early lactation fitted with abomasal and jugular artery catheters were used in a repeated 2×2crossover experiment.Treatments were abomasal infusion of saline or 200g·d-1 glucose.The experiment was consisted of two periods.Each period lasted 8dand there was a 14 dinterval between the two periods.RT-PCR was used to detect the mRNA expression of ACC,FAS,LPL,H-FABP,GPATand SCD.The results indicated that glucose infusion elevated blood glucose(P<0.05)and tended to elevated plasma insulin(P=0.06).Glucose infusion increased milk yield,decreased both milk fat yield and milk fat percentage(P<0.05).Analysis of fatty acid profile of milk fat reveled that glucose infusion decreased the yield of C18∶0and c9C18∶1(P<0.05)but had no significant effect on the yields of those de novo synthesized fatty acids(C4-C14)and those dual source fatty acids that may be preformed or de novo synthsized(C16).Glucose infusion had no significant effects on the mRNA experssion of acetyl coenzyme A carboxylase,fatty acid synthetase,lipoprotein lipase,fatty acid bonding protein,glycerol-3-phosphate acyltransferase,stearoyl CoA desaturase and fatty acid transfer protein.It was concluded that abomasal glucose infusion decreased milk fat synthesis mainly by decreasing the amount ofpre-formed fatty acids used for milk fat synthesis,had no significant effect on the expression of genes related to milk fat synthesis.The regulation of abomasal glucose infusion on milk fat synthesis occurred after transcription.