Effects of graded levels of dietary vitamin C on the growth, digestive capacity and intestinal microflora of juvenile Jian carp (Cyprinus carpio var. Jian)

A 60-day experiment was carried out to study the effects of vitamin C [ascorbic acid (AA)] on the growth, digestive enzyme activities and intestinal microbial population. Diets with six levels (0.0, 21.4, 45.1, 69.5, 93.6 and 142.1 mg AA kg-1 diet) of supplemental ascorbyl polyphosphate were fed to juvenile Jian carp (Cyprinus carpio var. Jian) (12.63 +/- 0.02 g). The specific growth rate (SGR), feed efficiency and productive protein value were significantly improved with increasing AA levels up to 45.1 mg AA kg-1 diet (P < 0.05). The hepatopancreas and muscle AA concentrations were increased with increasing dietary AA levels up to 69.5 and 45.1 mg kg-1 diet respectively (P < 0.05). The activities of intestinal trypsin, chymotrypsin, lipase, alpha-amylase, Na+, K+-ATPase, alkaline phosphatase, gamma-glutamyl transpeptidase and creatinkinase were all positively affected by the AA supplementation (P < 0.05). Intestinal Lactobacillus and Bacillus were increased with increasing AA levels up to 45.1 mg AA kg-1 diet (P < 0.05), while intestinal Escherichia coli decreased with increasing AA levels up to 45.1 mg AA kg-1 diet (P < 0.05). In conclusion, AA improve the digestive capacity and intestinal microbial population of Jian carp, and the dietary AA requirement for SGR of juvenile Jian carp was 40.9 mg AA kg-1 diet.