EFFECTS OF SUPPLEMENTATION OF NEUTRAL PROTEASE AND NEUTRAL PHYTASE IN FISH MEAL FREE DIET WITH LOW PHOSPHORUS LEVEL ON GROWTH, NUTRIENTS DIGESTIBILITY AND DEPOSITION OF JIAN CARP (CYPRINUS CARPIO VAR. JIAN)

To evaluate the effects of the supplementation of neutral protease and neutral phytase in fish meal free diet with low phosphorus level on the growth, nutrients digestibility, nutrients deposition, serum biochemical index, and intestinal morphology of Jian carp (Cyprinus carpio var. Jian), five diets were prepared as the positive control diet 5% fish meal, 1.5% Ca(H₂PO₄)₂, fish meal free diet (FMF) supplemented without or with 175 mg/kg protease, low phosphorus and fish meal free diet 1.0% Ca(H₂PO₄)₂, LP-FMF supplemented without or with 175 mg/kg protease+300 mg /kg phytase (LP-FMF+Pr+Ph), respectively, for a 10-weeks trial. The results indicated that the control group had the highest weight gain rate (WGR) and the lowest feed conversion ratio (FCR) among all groups (P<0.05). TheWGR, the retention ratios of protein and P, the digestibilities of protein and calcium of FMF group and LP-FMF group were significantly lower than those of control group (P<0.05). The supplementation of protease (FMF+protease) improved theWGR by 13.1% (P<0.05), and promoted the digestibilities of protein and calcium, and improved the foregut villus length, and decreased theFCR (P<0.05) compared with FMF group. The LP-FMF+Pr+Ph group showed the higher retention ratios of lipid, protein and phosphorus (P<0.05), the higher digestibilities of protein, phosphorus and calcium (P<0.05), the longer villus length and crypt depth, and the higher serum phosphorus level (P<0.05) than the LP-FMF group. These results indicated that the supplementation of protease in fish meal free diet and the supplementation of protease and phytase in low phosphorus and fish meal free diet could improve the growth performance, the digestibility and retention ratios of nutrients, and promote the intestinal development of Jian carp.