Effects Of Threonine On Lipid Metabolism In Pekin Ducks And Its Regulatory Mechanism

Five experiments were conducted to study the effects of threonine on lipids metabolism of Pekin duck and its mechanism.Experiment 1 was conducted to investigate the effects of Thr on hepatic lipid metabolism in Pekin ducks under different dietary CP levels.A completely randomized factorial design involved 3 CP levels(16%,19%,and 22%)and 5 Thr supplemental levels(0%,0.07%,0.14%,0.21%,and 0.28%).The results showed that dietary Thr supplementation improved the growth performance and breast muscle percentage at all CP level diets.Thr supplementation reduced the concentrations of total lipid,triglyceride,cholesterol in liver,and the plasma low density lipoprotein cholesterin concentration at 16%and 19%CP diets.Thr requirements based on quadratic broken-line model were 0.66%and 0.70%for optimal average daily gain(ADG),and 0.67%and 0.73%for breast muscle percentage of Pekin ducks from 1 to 21 days of age at 19%and 22%CP diets,respectively.The dietary Thr requirements,estimated ADG(55.18 vs.55.86 g/day/bird)and breast muscle percentage(2.79 vs.2.75%)of Pekin ducks had no difference between 19 and 22%CP diets according to the t-test results.Experiment 2 was conducted to evaluate the effects of Thr on hepatic lipid metabolism-related gene expressions in liver of Pekin ducks.A total of 240 one-day-old ducklings were randomly allotted according to average body weight to 1 of 5 dietary treatments with 6 replicate cages of 8 birds per cage for each treatment..The results showed that dietary Thr supplementation increased average daily gain,average daily feed intake,and abdominal fat percentage,while it decreased feed/gain,the hepatic contents of total lipid and triglyceride of Pekin ducks.Thr-unsupplemented control diet upregulated hepatic gene expressions related to lipid uptake,fatty acid synthesis,fatty acid ?-oxidation,ketogenesis,responsive genes to amino acid deficiency,and triglyceride transport of Pekin ducks.Experiment 3 was conducted to identify the underlying molecular changes caused by dietary threonine deficiency.180 one day old ducks were divided into three groups,including Thr deficiency group(Thr-D),Thr sufficiency group(Thr-S),and pair-fed group(Pair-F)fed Thr sufficient diet with similar daily feed intake with Thr-S group.The results showed that Thr-D and Pair-F groups had similar feed intake,but the weight gain and body weight in Thr-D group were lower than that in Pair-F group.Thr-D reduced the abdominal fat percentage,but increased hepatic triglyceride content compared with Thr-S and Pair-F groups.Thr-D changed some fatty acid contents in liver.RNA-sequence in liver sample indicated that Thr-unsupplemented increased hepatic lipid accumulation in ducks by increasing lipid synthesis and reduced lipid transport.Experiment 4 was conducted to determine the effects of dietary threonine on lipids metabolism in fat and meat type Pekin duck.At 15 days of age,192 ducks were selected from fat and meat type,respectively.And then allotted to one of three treatments with 8 replicates(8 ducks/cage),respectively.All ducks were fed the experimental diets for 21 days.The results showed that the feed intake and gain/feed ratio of fat type ducks were higher than that in meat type ducks,and the body weight and weight gain were similar between fat and meat type ducks.Dietary threonine deficiency or excess had no influence on growth performance of fat type ducks,and dietary threonine supplement improved the growth performance of meat type ducks.Fat type ducks had higher abdominal fat and sebum percentage,and lower breast muscle percentage than that in meat type ducks.Dietary threonine deficiency reduced breast and thigh muscle percentage,and dietary threonine deficiency or excess reduced abdominal fat and sebum percentage of meat type ducks.Meat type ducks had higher hepatic contents of total lipids,triglyceride,and cholesterol,and dietary threonine deficiency increased hepatic total lipid,cholesterol,and triglyceride contents in meat type ducks,but had no influence on hepatic lipids of fat type ducks.The plasma LDLC concentration was higher in meat type ducks than that in fat type ducks.The results of transcriptomics showed that dietary threonine deficiency increased the hepatic gene expressions related to arachidonic acid,glycerophospholipid,and linoleic acid metabolism,and reduced gene expressions of CYP7A1 and LIPC of meat type Pekin duck.Dietary threonine deficiency had no influence on gene expressions of abdominal fat and sebum in meat type Pekin duck.Dietary threonine deficiency had no influence on gene expressions of liver,abdominal,and sebum in fat type Pekin ducks.Experiment 5 was conducted to compare the differences of lipid metabolism between fat and meat type Pekin ducks by analyzing the transcriptomics data from experiment 4.The results showed that fat type Pekin ducks had higher expressions in liver related to fatty acid synthesis,triglyceride,and PLTP,LPIN and MOGAT than that in meat Pekin ducks.Fat type Pekin ducks had lower gene expressions of DGKB,DGKI,and PLB1 in abdominal fat than that in meat type Pekin ducks.Fat type Pekin ducks had higher expressions related to fatty acid and triglyceride metabolism,and lower expressions of LPL,GPD1,DGAT2,ATGL,PLIN1,ANGPTL4,and FABP6 in sebum than that in meat type Pekin ducks.In summary,1)Threonine deficiency in corn-wheat-peanut diet increased hepatic lipid deposition which related to the regulation of threonine on gene expressions of lipid metabolism.2)Threonine supplement into corn-wheat-peanut cake diet had different effects on lipid metabolism between fat and meat type Pekin ducks.3)There were differences in lipids metabolism between fat and meat type Pekin ducks.