Abstract
This study was designed to investigate the effects of dietary supplementation with different levels of DL-methionine (DL-Met) on growth performance, intestinal mucosal morphology and antioxidant capacity of Linwu ducks. The experiment was conducted to classify 330 healthy 49 days of age female Linwu ducks into 5 treatment groups with 6 replicates per treatment and fed diets with DL-Met levels of 2.5 g/kg, 3.0 g/kg, 3.5 g/kg, 4.0 g/kg, and 4.5 g/kg, respectively, for 21 days. The results showed that compared to the 2.5 g/kg group, the average daily weight gain (ADG) of Linwu ducks in the 3.5 g/kg group was significantly higher (P < 0.05), while the feed-to-gain ratio (FCR) of ducks in the 4.0 g/kg and 3.5 g/kg groups was similarly significantly decreased (P < 0.05). Additionally, the duodenal, jejunal, and ileum mucosal morphology was more structurally intact in the 3.5 g/kg and 4.0 g/kg groups, and the ratio of villus height to crypt depth (V/C) was significantly improved in the duodenum and ileum (P < 0.01). On the other hand, serum triglyceride (TG) and uric acid (BUN) levels were significantly (P < 0.05) decreased in the 3.5 g/kg group. Moreover, serum malondialdehyde (MDA) levels were significantly decreased (P < 0.05) in the 3.5 g/kg and 4.0 g/kg groups, while hepatic glutathione peroxidase (GPX) activity, GPX1, and glutathione S-transferase ɑ3 (GSTα3) mRNA expression levels were significantly increased (P < 0.05). Furthermore, hepatic total antioxidant capacity (T-AOC) activity was also significantly (P < 0.05) increased in the 3.5 g/kg group. In conclusion, dietary DL-Met supplementation could improve the growth performance of Linwu ducks by improving their redox status and intestinal mucosal morphology. Under the conditions of this experiment, the appropriate level of dietary Met supplementation for 49-70 days of age Linwu ducks is between 3.5 g/kg and 4.0 g/kg.