Effects of different levels of methionine and taurine in all-plant-protein diets on growth, physiology and antioxidant capacity of juvenile Megalobrama amblycephala

To explore the effect of supplementing methionine (Met) and taurine (Tau) in the all-plant-protein diets of juvenile Megalobrama amblycephala. Six experimental diets were prepared with three Met supplementary levels (2.5, 5.0 and 10.0 g/kg) and two Tau supplementary levels (1.0 and 2.0 g/kg), which were respectively recorded as M₁T₁ (measured values of Met and Tau were 7.5 and 1.7 g/kg), M₁T₂ (measured values of Met and Tau were 7.2 and 2.7 g/kg), M₂T₁ (measured values of Met and Tau were 7.9 and 1.7 g/kg), M₂T₂ (measured values of Met and Tau were 8.6 and 2.7 g/kg), M₃T₁ (measured values of Met and Tau were 11.8 and 1.6 g/kg) and M₃T₂ (measured values of Met and Tau were 12.5 and 2.8 g/kg). The growth performance, plasma physiology, and liver and intestine antioxidant capacity of juvenile M. amblycephala were measured after a 10-week feeding trial. The weight gain rate (WGR), specific growth rate (SGR), and feed conversion ratio (FCR) of each group were affected by dietary Met content and the interaction between Met and Tau. The M₂T₂ group showed the highest WGR and SGR, and the lowest FCR. Plasma alkaline phosphatase (ALP) was significantly affected by dietary Met content and the interaction, and plasma alanine aminotransferase (ALT) was significantly affected by dietary Tau content. At T₁ level, ALP and ALT decreased significantly with the increase of dietary Met content. The activities of catalase (CAT) in the liver and intestine were significantly affected by the interaction, and the CAT activity was the highest in the M₂T₂ group. The level of intestinal glutathione (GSH) was affected by dietary Met and Tau content, and the level of malondialdehyde (MDA) was affected by the interaction. At T₂ level, the contents of GSH and MDA decreased with the increase of dietary Met content. The activities of intestinal amylase (AMS) and trypsin (TPS) were affected by the interaction between Met and Tau. At the T₁ level, the activity of TPS increased first and then decreased with the increase of dietary Met content, and the activity was highest in the M₂T₁ group. The dietary levels of Met at 8.6 g/kg and Tau at 2.7 g/kg in the all-plant-protein diet significantly improved the growth performance, feed utilization and liver and intestine antioxidant capacity of juvenile M. amblycephala, which showed a synergistic effect of the appropriate addition of Met and Tau.