Dietary threonine supplementation improves hepatic lipid metabolism of Pekin ducks

The present study was conducted to evaluate the regulatory role of threonine (Thr) on hepatic lipid metabolism by determining the effects of dietary Thr concentration on lipid deposition and on genes related to lipid expression in the liver of Pekin duck. In total, 240 1-day-old ducklings were randomly allocated according to the average bodyweight to one of five dietary treatments with six replicate cages of eight birds per cage for each treatment. Birds were fed diets with 0.52%, 0.59%, 0.66%, 0.73% and 0.80% Thr (as-fed basis) from 1 to 21 days of age respectively. The results showed that dietary Thr supplementation increased average daily gain (P < 0.0001), average daily feed intake (P < 0.0001) and abdominal fat percentage (P < 0.04), while it decreased feed to gain ratio (P < 0.0001), the hepatic contents of total lipid (P < 0.003) and triglycerides (P < 0.003) of Pekin ducks. However, dietary Thr supplementation had no influence (P > 0.05) on the concentration of hepatic cholesterol, and plasma amino acids and biochemical parameters of Pekin ducks. Moreover, Thr-unsupplemented control diet upregulated (P < 0.05) hepatic gene expression related to lipid uptake (fatty acid-binding protein, apolipoprotein A4, lipoprotein lipase), fatty acid synthesis (sterol regulatory element-binding protein 1c, malic enzyme), fatty acid β-oxidation (peroxisome proliferator-activated receptor α, fatty acyl– coenzyme A (CoA) oxidase), ketogenesis (hydroxymethylglutaryl–CoA synthase 1, and acetyl–CoA synthetase1), responsive genes to amino acid deficiency (general control non-derepressible 2 (GCN2), GCN1, eukaryotic initiation factor 2α, impact RWD domain protein (IMPACT)), and triglyceride transport (apolipoprotein B) of Pekin ducks. In addition, dietary Thr deficiency had no effect on the expression of stearoyl CoA desaturase, fatty acid synthase, and ATP–citrate lyase in the liver of Pekin ducks. It is suggested that dietary Thr supplementation improved hepatic lipid metabolism of Pekin ducks by regulating lipid synthesis, transport and oxidation.