Protease exógena em dietas para tilápias do Nilo (Oreochromis niloticus)

Abstract

Protease is an enzyme characterized by its action on protein bonds and can improve the assimilation of nutrients from protein ingredients. Positive effects of its inclusion have been identified in many species, due to improved feed efficiency and protein synthesis. Factors linked to feed processing, the level and form of protease inclusion influence its efficiency, as well as the composition of the diets. Therefore, the objective was to evaluate whether there are effects of its inclusion in tilapia diets on performance parameters, biochemical metabolism, digestive enzyme activity, nutrient digestibility, and gene expression. For this, two feeding trials lasting 49 days were carried out. In feeding trial I, five levels of exogenous protease (control; 194; 316; 390; 600 mg/kg) were tested in a diet formulated with feather meal. In feeding trial II, the experimental design was a 3x2 factorial, consisting of the formulation of three diets and two levels of exogenous protease (0 and 440 mg/kg). The proportion of protein in the diet was increased with the inclusion of soybean meal (SM) replacing fish waste meal. The treatments were named: SM1-0; SM1-440; SM3-0; SM3-440; SM6-0; SM6-440. At the end of the feeding trials I and II, fish performance and health parameters were evaluated. In feeding trial I, there was better performance, nutrient utilization and greater expression of the growth hormone receptor (GHR) in the liver with 390 mg/kg of protease in the diet compared to the control. Protein metabolism improved with increased concentration of total proteins and amino acids (AA) and lower ammonia content. The greater inclusion of protease (600 mg/kg) in the diet stimulated an increase in the number of erythrocytes and a lower mean corpuscular volume in fish. In feeding trial II, it was observed that the SM1 group (SM1-0 and SM1-440) had better growth, protein efficiency rate and feed conversion. In general, the exogenous protease stimulated endogenous trypsin activity, resulting in better protein digestibility, and intestinal morphometry in the group with the highest SM (SM6-440). In fish that received the SM3-440 diet, there was a higher albumin and globulin content compared to the SM1-440 diet, but did not differ from the SM6-440 diet, indicating an innate response, due to the increased availability of proteins and AA. In conclusion, the optimal level of protease inclusion was 440 mg/kg. Among the diets, SM3-440 demonstrated a better nutritional and physiological balance. The inclusion of protease allowed the increase in soybean meal (SM) without negatively affecting the growth of Nile tilapia.