Effects of L-malic acid on intestinal histology and function, and TCA cycle efficiency of the liver of Gift tilapia (Oreochromis niloticus)

This experiment was conducted to study the effects of dietary L-malic acid levels on intestinal histology and function,and TCA cycle efficiency in liver of Gift tilapia.The experimental diets supplemented with 0(control group),1.0,2.0,4.0,8.0,16.0 and 32.0 g/kg L-malic acid had been fed to juvenile tilapia with initial body weight of(37.94±0.09)g for 154 days.420 juvenile tilapia were randomly divided into seven groups and each group had three replicates(20 fishes for each replicate).The results showed that:With the increment of L-malic acid supplement,the villus height,villus density and muscular thickness of foregut and midgut reached the highest in 16.0 g/kg group which was significantly higher than those in control group(P<0.05),and the villus height,villus density and muscular thickness of hindgut gradually decreased(P<0.05).Intestinal amylase and lipase activities reached the highest in 1.0 g/kg group which were significantly higher than those in control group(P<0.05).The protease activity,and the content of ATP increased gradually with the increased level of L-malic acid(P<0.05).The activity of Na⁺-K⁺-ATPase,and the intestinal content of EGF and EGFR reached the highest in 16.0 g/kg group,meanwhile citrate synthase activity reached the highest in 8.0 g/kg group.This study indicates that in the dietary of Gift tilapia,a proper addition of L-malic acid(1.0-8.0 g/kg)can improve the morphology of foregut and midgut,promote the proliferation of intestinal mucosal epithelial cell,and improve the ability of intestinal digestion and absorption and the efficiency of liver TCA cycle.