Effects of dietary alfalfa Medicago falcata L. powder on growth performance, nonspecific immunity and digestive enzyme activity of Lateolabrax japonicus

Abstract

Six graded levels of dietary alfalfa Medicago falcata L. powder (0, 5, 10, 15, 20 and 25 g/kg diet, respectively) were fed to Lateolabrax japonicus (initial body weight: 11.41 ± 0.06 g; initial body length: 10.33 ± 0.12 cm) in triplicate groups for 4 weeks in a flow-through system to investigate the effects of alfalfa powder on the growth performance, nonspecific immunity and digestive enzyme activity. The results showed that alfalfa powder reduced the feed conversion ratio (FCR), with the lowest value obtained at 20 g/kg diet among all groups (p < 0.05). The serum total soluble protein (TP) content, activity of lysozyme (LZM) and total superoxide dismutase (T-SOD) were increased first then remained more or less stable; the alkaline phosphatase (AKP) was maintained stable first then sharply increased with the increasing dietary alfalfa powder levels. The trypsin and lipase (LPS) activity of fish was significantly increased at 20 g/kg diet, compared to the control group (p < 0.05). Regression analyses of FCR, TP, LZM, T-SOD, LPS and trypsin indicated that the optimal supplement amount was 17.75–21.48 g/kg diet. Combined with the significant difference analyses obtained from the current study, we suggest the additional amount of alfalfa should be about 20 g/kg diet.