Effects of dietary microbial protease on growth performance, nutrient apparent digestibility, hepatic antioxidant capacity, protease activities and intestinal microflora in juvenile genetically improved farmed tilapia, Oreochromis niloticus

Abstract

The study was to evaluate the effects of four types of microbial protease on growth performance, nutritional composition, apparent digestibility coefficients (ADC), physiological parameters and microbiota of genetically improved farmed tilapia (GIFT, Oreochromis niloticus). Six diets were prepared, including a positive control diet (protein 300 g/kg, high protein group, HP) and one negative control diet (protein 280 g/kg, low protein group, LP) and four proteases were added to the low protein diets, included HuPro protease (LPH), acid protease (LPAC), neutral protease (LPN) and alkaline protease (LPAK). Compared with the fish fed LP diet, the weight gain rate (WGR), specific growth rate (SGR), feed conversion rate (FCR), protein efficiency ratio (PER) and feed intake ratio (FIR) were improved in fish fed LPH diet. The ADC of dry matter in LPH diet was improved. The serum total protein (TP) in LPH diet was higher than the LP diets. The activities of total antioxidant capacity (T-AOC) and catalase (CAT) in LPH group was higher than the LP and HP group, respectively. The protease activities of stomach and gut in fish fed LPH diet was higher than LP group. Shannon and Simpson indices in LPH group were higher than the LP group. The abundance of Fusobacteria in the six groups reached more than 70 % at the phylum level, and the largest difference in the relative abundance at the genus level was Cetobacterium. In conclusion, this study demonstrates the positive effects of HuPro protease on tilapias and selection of HuPro protease to the low protein diet is suitable.