Beneficial effects of phytase and/or protease on growth performance, digestive ability, immune response and muscle amino acid profile in low phosphorus and/or low fish meal gibel carp (Carassius auratus gibelio) diets

Abstract

A 10-week feeding trial was conducted to investigate the effects of individual and combined inclusion of phytase and protease on the growth performance, digestive ability, immune response and muscle amino acid profile of gibel carp (Carassius auratus gibelio) fed low phosphorus (LP) and/or low fish meal (LFM) diets. Seven experimental diets were designed: 1) Normal diet [PC, 15 g/kg Ca(H2PO4)2 and 80 g/kg fish meal], 2) Low P diet [10 g/kg Ca(H2PO4)2 and 80 g/kg fish meal], 3) LP + 0.4 g/kg phytase diet (LP + Ph), 4) Low fish meal diet [LFM, 15 g/kg Ca(H2PO4)2 and 50 g/kg fish meal], 5) LFM + 0.5 g/kg protease diet (LFM + Pr), 6) Low P and Low fish meal diet [LP-LFM, 10 g/kg Ca(H2PO4)2 and 50 g/kg fish meal] and 7) LP-LFM + 0.4 g/kg phytase +0.5 g/kg protease diet (LP-LFM + Ph + Pr). The results showed that the growth performance, whole body composition, nutrient digestibility, immunological indices, and muscle amino acid contents of gibel carp fed the LP, LFM and LP-LFM diets were dramatically lower than those of carp fed the normal diet (P<0.05). However, compared the LP-LFM, LFM and LP groups, dietary addition of phytase + protease, protease and phytase, respectively, (1) improved the special growth rate (SGR), weight gain rate (WGR), ADC of dry matter, crude protein and P; (2) upregulated the activities of lipase, trypsin, amylase and chymotrypsin in the liver and intestine; (3) increased liver lysozyme (LZM), superoxide dismutase (SOD), glutathione peroxidase (GPx) and total antioxidant capacity (T-AOC) levels, intestinal secreted immunoglobulin A (sIgA), complement 4 (C4) and C3 levels; (4) increased the contents of amino acids, for example, valine, leucine and methionine, in the muscle. Moreover, when both phytase and protease were added simultaneously, they had a better promoting effect than when individual added. It can be concluded that a reduction of dietary P and fish meal for gibel carp has side effects on growth performance, while phytase and protease could mitigate these effects by improving the digestive ability and immune response of gibel carp.