Effects of dietary methionine on productivity, reproductive performance, antioxidant capacity, ovalbumin and antioxidant-related gene expression in laying duck breeders

The study investigated whether dietary methionine (Met) affects egg weight and antioxidant status through regulating gene expression of ovalbumin (OVAL), nuclear factor erythroid 2 like 2 (Nrf2) and haem oxygenase 1 (HO-1) in laying duck breeders. Longyan duck breeders (n 540, 19 weeks) were randomly assigned to six treatments with six replicates of fifteen birds each. Breeders were fed diets with six Met levels (2·00, 2·75, 3·50, 4·25, 5·00 and 5·75 g/kg) for 24 weeks. The egg weight (g), egg mass (g/d), feed conversion ratio, hatchability, 1-d duckling weight, albumen weight, albumen proportion and OVAL mRNA level improved with dietary Met levels, whereas yolk proportion decreased (P<0·05). The weight of total large yellow follicles increased linearly (P<0·001) and quadratically (P<0·05) with dietary Met concentration, and their weight relative to ovarian weight showed a linear (P<0·05) effect. Dietary Met level had a linear (P<0·05) and quadratic (P<0·001) effect on the gene expression of glutathione peroxidase (GPX1), HO-1 and Nrf2, and quadratically (P<0·05) increased contents of GPX and total antioxidant capacity (T-AOC) in liver of duck breeders. In addition, maternal dietary Met enhanced gene expression of GPX1, HO-1 and Nrf2, increased contents of GPX and T-AOC and reduced carbonylated protein in the brains of hatchlings. Overall, dietary Met concentration affected egg weight and albumen weight in laying duck breeders, which was partly due to gene expression of OVAL in oviduct magnum. A diet containing 4·0 g Met/kg would achieve optimal hepatic GPX1 and Nrf2 expression, maximise the activity of GPX and minimise lipid peroxidation.