Metabolism and Nutrition: Amino Acid Posters

All procedures of our experiments were approved by the animal care and welfare committee of the Institute of Animal Science of Chinese Academy of Agricultural Sciences. Two dose-response experiments were conducted to assess the bioefficacy and toxicity of DL-methionine hydroxy analog free acid (MHA-FA) relative to DL-methionine (DLM) in White Pekin ducks. In experiment 1, the methionine-deficient basal diets were supplemented with 5 levels of DLM (0.3, 0.6, 1.0, 1.5, and 2.1 g/kg) or 5 equimolar levels of MHA-FA (0.34, 0.68, 1.13, 1.70, and 2.39 g/kg), respectively. A total of 704 7-d-old male White Pekin ducklings were assigned to 11 experimental treatments, each containing 8 replicate pens with 8 birds per pen. These birds were reared in raised wire-floor pens from 7 to 42 d of age. In experiment 2, the methionine-adequate control diets were supplemented with 30g/ kg DLM or equimolar 33.9 g/kg MHA-FA, respectively. A total of 126 7-d-old male White Pekin ducklings were divided to 3 experimental treatments, each containing 6 replicate pens with 7 birds per pen. These birds were reared in raised wire-floor pens from 7 to 14 d of age. At the end of both experiments, the weight gain, feed intake, and feed conversion efficiency of ducklings from each treatment were measured. In our study, supplementation of DLM or MHA-FA to the methioninedeficient basal diets could all improve weight gain of Pekin ducks significantly (P < 0.05). However, according to the slope-ratio assay on equimolar basis, the bioavailabilities of MHA-FA relative to DLM for weight gain were 67%. On the other hand, excess DLM and MHA-FA caused significant decrease in weight gain and feed intake of ducklings (P < 0.05) but MHA-FA was less growth-depressing and lethal than equimolar DLM (P < 0.05).