细粉碎小麦诱导亚急性瘤胃酸中毒对奶牛乳脂合成和肝脂肪合成关键酶基因表达量的影响

Effect of Finely Ground Wheat Induced Subacute Ruminal Acidosis on Milk Fat Synthesis and Expression of Key Lipogenic Enzyme Genes in Liver Tissue in Dairy Cows

旨在通过饲喂大量细粉碎小麦诱导奶牛发生亚急性瘤胃酸中毒(SARA),研究SARA对奶牛乳脂合成、肝脂肪合成关键酶及其调节因子mRNA表达量的影响,并用甜菜颗粒粕(BP)来替代玉米,试图缓解SARA。试验选取8头泌乳中期经产荷斯坦奶牛(4头带有瘤胃瘘管),采用自身对照试验设计,共分为4期(17d/期),分别饲喂4种日粮:1)对照期:全混合日粮(TMR)不含小麦(W0);2)过渡期:TMR含有10%的细粉碎小麦(W10);3)SARA诱导期:TMR含有20%的细粉碎小麦(W20);4)SARA调控期:在W20处理基础上,用10%的BP替代10%玉米(BP10)。试验结果得出:与W0处理相比,W20处理降低了瘤胃平均pH(6.37~5.94,P<0.01)和最低pH(5.99~5.41,P<0.01),pH低于5.6的时间大于180min·d-1,诱导产生了SARA;BP替代玉米时增加了瘤胃平均pH(5.94~6.05)和最低pH(5.41~5.63)。干物质采食量和产奶量未受影响,但W20和BP10处理奶牛的乳脂率和乳脂产量低于(P<0.01)W0处理。W20处理血浆葡萄糖和胰岛素浓度高于(P<0.01)对照组,而血脂浓度低于(P<0.01)对照组。W20处理肝组织中乙酰辅酶A羧化酶α(ACACA)(P=0.03)、脂肪酸合成酶(FASN)(P=0.05)和胆固醇调节元件结合蛋白1(SREBF1)(P<0.01)基因的mRNA相对表达量均高于W0处理,但在W10、W20和BP10 3个处理间差异不显著。结果提示,奶牛发生SARA时可引起乳脂下降和肝中脂肪合成关键酶其调节因子基因表达量增加;饲喂高精料日粮时用甜菜颗粒粕替代部分玉米可减缓SARA的发生。

The aims of this study were to determine the variation of milk fat synthesis and expression of lipid anabolism related genes in liver tissue triggered by feeding a large amount of finely ground wheat inducing subacute ruminal acidosis(SARA);and evaluate the ability of pelleted beet pulp(BP)as a substitute for ground corn to alleviate SARA.Eight mid-lactation Holstein cows were fed four diets during four successive 17-day periods:1)control period:total mixed ration(TMR)containing 0%finely ground wheat(FGW)(W0);2)transition period:TMR containing 10% FGW(W10);3)SARA induction period:TMR containing 20% FGW(W20);and 4)SARA regulation period:TMR containing 10%BP as a replacement for 10%ground corn(BP10)on the basis of W20.The result shown that,compared to W0,the SARA induction protocol re-duced(P<0.01)the mean ruminal pH from 6.37 to 5.94,the minimum ruminal pH decreased(P<0.01)from 5.99 to 5.41 from control period to SARA induction period,and the time of pH<5.6was more than 180min·d-1,SARA was induced.Mean ruminal pH increased from5.94 to 6.05,and minimum pH increased from 5.41 to 5.63,when BP was substituted for corn.Dry matter intake and milk yield were not affected by the dietary treatments,however,milk fat percentage and yield were reduced(P<0.01)in the W20 and BP10treatments than that in the W0 treatment.Cows fed the W20 diet had a lower(P<0.01)plasma concentration of triglyceride,and a higher(P<0.01)plasma concentration of glucose and insulin than cows fed the W0 diet.Liver tissue relative expression of acetyl-CoA carboxylase alpha(ACACA)(P=0.03),FA synthase(FASN)(P=0.05),sterol-response element binding protein 1(SREBF1)(P<0.01)was increased,but there were no significant differences among the W10,W20 and BP10diets.The results indicate that the SARA could decrease of milk fat and increase the relative expression of key lipid synthesis genes in liver tissue.The partly substitution of pelleted BP for ground corn in a high-concentrate diet could reduce the risk of SARA in dairy cows.