| The study was conducted to investigate the effects of methionine (Met) sources and levels on growth performance, carcass traits, nutrition utilization and antioxidant ability of meat ducks. Nine hundred and forty-five 1-d-old ducks were randomly assigned to 2 Met sources (DL-met.DLM and 2-hydroxy-4-(methylthio)butanoate,HMTBA),4 Met levels (80%,100%,120% and 140%) and one basal diet without DLM or HMTBA supplementation in a 2×4+1 factorial arrangement (7 replicate pens; 15 ducks per pen). The levels of methionine were 0.415%,0.45%,0.485%,0.52% at starter phase (1-14d) and 0.319%,0.34%,0.361%,0.382% at grower phase (15-35d).The results showed that 1) BW (d 14,35), BWG (d 1-14 and 1-35), feed intake (FI,d 1-14) of ducks fed diets with DLM or HMTBA supplementation were significantly higher (P<0.01) than ducks fed the basal diet. Feed to gain ration (F/G) in 1-14d,15-35d and 1-35d of ducks were significantly decreased (P<0.05) when DLM and HMTBA were added. Compared to the basal diet treatment, the supplementation of DLM and HMTBA significantly increased (P<0.05) feather score, the 4th primary feather length and the weight of eviscerated carcass on 35d, also the content of serum total protein(TP), albumin(ALB) and globulin(GLB) of ducks at 14d of age.2) Based on equimolar addition, BW (d 35) and BWG (d 1-35) of ducks fed 80% HMTBA diet were significantly lower (P<0.05) than ducks fed 80% DLM diet. Serum GLB content, hepatic total antioxidant capacity and glutathione peroxidase (GSH-Px) activity at 14d of age and BWG at grower phase of ducks fed diets with DLM supplementation were better (P<0.05) compared to ducks fed diets with HMTBA addition. However, feather score (d 35) of ducks fed diets with HMTBA were higher (P<0.05) than ducks fed diets with DLM.3) Feed to gain ratio (d 1-14) of ducks fed diet with 120% and 140% Met were lower (P<0.05) than ducks fed diets with 80% Met. Hepatic malondialdehyde(MDA) content of ducks at 35 d of age fed diets containing 80% and 140% Met were lower (P<0.05) than ducks fed diets containing 100% Met. There were significant interactions (P<0.05) between methionine sources and levels for serum TP and GLB contents of ducks at 14d of age and serum GSH-Px activity of ducks at 35d of age.4) With DLM as the Met source, the optimum Met requirement of ducks based on BWG and F/G (d 1-35), the 4th primary feather length and the weight of eviscerated carcass at 35 d of age were 0.433%,0.444%,0.444% and 0.441% at the starter phase, and 0.330%,0.337%,0.336% and 0.334% at the grower phase, respectively by the quadratic regression. But with HMTBA as the Met source, the optimum Met requirement of ducks based on F/G (d 1-35), the 4th primary feather length and the weight of eviscerated carcass at 35 d of age were 0.476%,0.506% and 0.50% at the starter phase, and 0.356%,0.375% and 0.370% at the grower phase, respectively by the quadratic regression.These results suggested that the supplementation of DLM or HMTBA in the basal diet could improve growth performance, feather growth and carcass traits of ducks. Based on equimolar added, growth performance of ducks fed 80% HMTBA diet were lower than ducks fed 80% DLM diet, but there were no significant differences between HMTBA and DLM groups under 100%,120% and 140% levels, respectively. Ducks fed diets with DLM had better BWG at grower phase and serum GLB content, hepatic total antioxidant capacity and glutathione peroxidase activity at starter phase compared to ducks fed diets with HMTBA. But feather score (d 35) of ducks fed HMTBA diets was better than ducks fed DLM diets. Based on growth performance (d 1-35), the 4th primary feather length and the weight of eviscerated carcass at 35 d of age, the optimal Met requirement of ducks were 0.440% at starter phase and 0.334% at grower phase with DLM as methionine source, when using HMTBA as methionine source, the optimal methionine levels were 0.494% at starter phase and 0.367% at growth phase. |
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