Effect of dietary protein level on digestive enzyme activity and histological structure in intestine and liver of juvenile Schizopygopsis younghusbandi

To explore the effects of different feed protein levels on the digestive enzyme activity and histological structure in the intestine and liver of juvenile Schizopygopsis younghusbandi, we designed six kinds of equal-energy experimental feeds with different protein levels (20%, 25%, 30%, 35%, 40%, 45%) to feed the juveniles with initial body mass of (22.42±0.56) g for 60 d. The results show that with the increase of feed protein level, the protease activity in intestine and liver increased first then declined. The protease activity in 35% protein group was significantly higher than that in the other groups (P<0.05). The lipase and amylase activities reduced significantly (P<0.05). The wall thickness and villus height of foregut, midgut and hindgut all increased and then decreased (P<0.05). The wall thickness of foregut and midgut were highest in 30% group, while the wall thickness of the hindgut was highest in the 35% group. The villus height of foregut, midgut and hindgut were highest in 30% group. Feed protein level higher than 35% may damage liver tissue structure. Under this condition, considering the digestive enzymes activity and histological structure of intestines and liver, the optimum protein level of juvenile S. younghusbandi should be 30%.