Effect Of Glucose-insulin On The Milk Fat And Genes Of Key Enzyme Involved In Milk Lipid Synthesis In Goat

The study was divided into two experiments, respectively the abomasal glucose infusionand hyperinsulinemic-euglycemic clamp to examine the effects of glucose and insulin on themilk fat synthesis in the diet-induced MFD by analysing the milk contents,plasmametabolites and the genes involved in milk lipid synthesis in the mammary gland.Experiment one： Four laoshan lactating dairy goats fitted with abomasal fistulae andembedded carotid under the skin, were used a balanced2×2crossover design with twotreatments consisting of a8d abomasal glucose infusion of either saline (control) or200g/dglucose infusion, observing the lactating capability, plasma metabolites and the mRNAexpression of the genes involved in milk lipid synthesis in the mammary gland. The resultsshow:①Infusing200g/d glucose increased the milk yield (P<0.05), and significantlydecreased milk fat content and yield (P<0.05). The milk fat content and yield were reduced33%and24.2%. The lactose content was decreased significantly with200g/d glucoseinfusion (P<0.05), but the lactose yield increased markedly. The content of protein and SNFwere not affected by the infusion of glucose.②Plasma glucose concentration increased inthe200g/d doze glucose group compared with the control. The concentration of plasmainsulin had a tendence to be increased (P=0.06).③Compared with control, the200g/ddoze treatment had no significant effect on the de novo fat acid concentration (C4-C14:1) andthe arise from two sources C16:0+C16:1,but markedly decreased the uptake of preformedlong chain fatty acid (≥C16)(P<0.05).④The200g/d doze glucose treatment had no effectson the expression of genes (ACC、FAS、LPL、H-FABP、GPAT、SCD）involved in milklipid synthesis in the mammary gland.Experiment two: Three late lactating laoshan dairy goats were subjected tohyperinsulinemic-euglycemic clamp by intravenous injection of glucose and insulin, and theinsulin doze was120μg/h. The whole trial was divided into four stages: the control period,the recovery period, insulin-clamp treating period and the period after finishing theinsulin-clamp.The results show:①The insulin-clamp treatment had no effects on the milk yield and lactosecontent, but significantly decreased the content of milk fat、 protein、 SNF(P<0.01), also decreased the milk fat yield (P<0.01). After the insulin-clamp finishing, milk fat content andyield increased gradually, and had no changes on the12h、24h after stopping theinsulin-clamp compared with the insulin-clamp treating period, but decreased markedlycompared with the control(P<0.01). On the time of36h、48h after finishing the insulin-clamp,milk fat content and yield increased significantly compared with clamp-treating period, buthad no change compared with control period.②The insulin-clamp treatment had no effectson the glucose concentration, markedly increased plasma insulin concentration(P<0.01).③Compared with the period of control, the insulin-clamp treating decreased both the de novofatty acids(C4-C14) and the long chain fatty acid (≥C16)yields(P<0.01,P<0.05). After theinsulin-clamp finishing, the yield of fatty acids were up-regulated gradually; the ratio of UFAand SFA(C14:1/C14:0； C16:1/C16:0) increased during the insulin-clamp treating periodcompared with control.④The mRNA expression of genes(ACC、FAS、LPL、H-FABP、GPAT、 SCD） involved in milk lipid synthesis in the mammary gland had no significantchanges during the insulin-clamp treating period and the period after the clamp finishing,compared with control.Conclusion: Although abomasal glucose infusion and the hyperinsulinemic-euglycemicclamp in goats didn’t affect the genes involved in lipid synthesis, but both decreased the milkfat content and yield, changed the milk fatty acid composition. The main function of insulinon the milk fat depression is to reduce the number of long chain fatty acids.