Effects of exogenous xylanase supplementation in plant protein‐enriched diets on growth performance,intestinal enzyme activities and microflora of juvenile Jian carp (Cyprinus carpio var. Jian)

A total of 900 juvenile Jian carp (Cyprinus carpio var. Jian) (7.99 ± 0.02 g) were fed diets containing graded levels of xylanase at 220 (unsupplemented control), 650, 1070, 1480, 1810 and 2470 U kg^?1 diet for 10 weeks to investigate the effects of xylanase levels on growth performance, intestinal enzyme activities and microflora. The per cent weight gain, feed efficiency, protein efficiency ratio, protein production value, lipid production value, ash production value, calcium production value and phosphorus retention ratio were significantly improved with increasing levels of xylanase up to a point, and thereafter declined (P < 0.05). The activities of trypsin, chymotrypsin, lipase and amylase in the hepatopancreas and intestine, activities of alkaline phosphatase, Na⁺, K⁺‐ATPase, creatine kinase and γ‐glutamyl transpeptidase in three intestinal segments were improved by dietary xylanase (P < 0.05). The amounts of Lactobacillus, Escherichia coli and Aeromonas were significantly affected by dietary xylanase levels (P < 0.05). In conclusion, xylanase supplementation improved growth performance, enhanced intestinal enzyme activities and influenced the balance of intestinal microflora of juvenile Jian carp. The optimal level of xylanase in juvenile Jian carp (7.99–99.16 g) based on PWG was 1259 U kg^?1 diet by the quadratic regression analysis.