Estimation of dietary selenium requirement for Chinese egg-laying ducks.

The purpose of this study was to estimate the selenium (Se) requirement of egg-laying ducks based on daily egg production and the selenoprotein glutathione peroxidase (Gpx). Five-hundred and forty laying ducks were divided into six treatments, each containing six replicates of 15 ducks. The birds were caged individually and received a Se-deficient basal diet (0.04 mg/kg) or diets supplemented with 0.08, 0.16, 0.24, 0.32, 0.40 mg/kg Se (as sodium selenite) for 6 months. The experiment consisted of two periods: an early-laying period of 2 months and the peak-laying period of 4 months. Egg production and feed intake were recorded daily. At the end of the experiment, blood samples were drawn for determination of Gpx activity in plasma (Gpx3) and in erythrocytes (Gpx1). Hepatic Gpx1 activity and relative expression of Gpx1 mRNA were also determined. Eggs (n = 6) were sampled for quality determination and Se content at the end of the experiment. The activities of plasma Gpx3, erythrocyte Gpx1 and liver Gpx1 increased in a quadratic manner (P < 0.001) with increasing supplemental Se. The mRNA abundance of hepatic Gpx1 increased linearly (P < 0.001) with dietary Se supplementation. Egg shell thickness was significantly reduced in the ducks fed 0.44 mg Se/kg (P < 0.05), indicating that higher dietary Se tends to compromise egg shell quality. Yolk and albumen contents of Se increased linearly (P < 0.0001) with dietary Se supplementation. Using quadratic broken line models, the Se requirement for daily egg production was 0.18 mg/kg for early-laying ducks and 0.24 mg/kg for peak-laying ducks; for optimal function of Gpx (peak-laying ducks), it was 0.37 mg Se/kg. The data on the function and requirement of minerals is insufficient for egg-laying ducks despite the large-scale laying duck production in Asia. Selenium deficiency leads to low antioxidant enzyme activities in ducks and the selenium requirement for laying ducks was obtained based on the egg production and activities of antioxidant enzymes in this study. Required selenium intake is important for the functions of antioxidant enzyme in production birds and animals. [ABSTRACT FROM AUTHOR]