Proteases are the enzymes responsible for the hydrolysis of complex proteins into simpler units for better digestion and absorption of nutrients. This study was conducted to determine the optimum supplementation level and effects of dietary protease addition in poultry by-product meal-based diet (PBM) on growth performance, nutrient digestibility, digestive enzyme activities and physiochemical parameters of juvenile rohu, Labeo rohita (initial weight: 11.33 ± 0.02 g). For this purpose, seven iso-nitrogenous and iso-lipidic experimental diets were formulated to contain a positive control (PC) diet (containing fishmeal and no protease), a negative control (NC) diet (containing PBM and no protease) and five other PBM-based diets supplemented with exogenous protease at the levels of 150, 300, 450, 600 and 750 mg/kg diet. Results indicated that growth performance and body indices of fish fed protease supplemented diets were higher (p < 0.05) compared with those fed the NC diet, while maximum increase was recorded at 450 mg/kg protease supplementation level, which was similar to the PC diet (p > 0.05). Protease supplementation up to 450 mg/kg level linearly improved (p < 0.05) the whole-body proximate composition and digestibility of dry matter (DM), crude protein (CP), crude lipid (CL) and crude ash (CA) in rohu juveniles. A similar trend (p < 0.05) was observed in the activities of amylases, lipases and proteases in intestinal and hepatopancreatic tissues, peaking at 450 mg/kg which was also similar (p > 0.05) to the PC diet. Protease supplementation significantly improved (p < 0.05) haemoglobin (Hb), haematocrit (Htc) and red blood cells (RBCs) of juveniles while, white blood cells (WBCs) and serum indices remained unaffected (p > 0.05). Based on quadratic regression analysis, the optimal dietary protease supplementation in PBM-based diet for rohu was 433 mg/kg. Conclusively, increase in protease supplementation from 0 to 450 mg/kg levels improved the fish performance and decreased thereafter with further increase in protease levels (600–750 mg/kg).

中文翻译：

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蛋白酶补充家禽副产品粕为主的日粮对罗胡 (Labeo rohita) 生长、营养消化率和消化酶活性的影响

蛋白酶是负责将复杂蛋白质水解成更简单单元以更好地消化和吸收营养的酶。本研究旨在确定家禽副产品粕型日粮 (PBM) 中添加日粮蛋白酶的最佳补充水平和对罗胡幼鱼 ( Labeo rohita ) 生长性能、养分消化率、消化酶活性和理化参数的影响。（初始重量：11.33 ± 0.02 克）。为此目的，配制了七种异氮和异脂实验日粮，以包含阳性对照（PC）日粮（含鱼粉且不含蛋白酶）、阴性对照（NC）日粮（含PBM且不含蛋白酶）和其他五种以 150、300、450、600 和 750 mg/kg 饮食水平补充外源蛋白酶的基于 PBM 的饮食。结果表明，与饲喂 NC 日粮相比，添加蛋白酶日粮的鱼的生长性能和体指数更高（p  < 0.05），而在添加蛋白酶水平 450 mg/kg 时记录到最大增幅，这与 PC 日粮相似( p  > 0.05)。蛋白酶补充剂高达 450 mg/kg 水平线性改善（p < 0.05) 肉豆幼体干物质 (DM)、粗蛋白 (CP)、粗脂质 (CL) 和粗灰分 (CA) 的全身近似组成和消化率。在肠道和肝胰腺组织中的淀粉酶、脂肪酶和蛋白酶的活性也观察到了相似的趋势（p  < 0.05），峰值为 450 mg/kg，这也与 PC 饮食相似（ p > 0.05）。蛋白酶补充剂显着改善（p  < 0.05）青少年的血红蛋白（Hb）、红细胞比容（Htc）和红细胞（RBC），而白细胞（WBC）和血清指标不受影响（p > 0.05)。基于二次回归分析，在基于PBM的日粮中，罗胡的最佳日粮蛋白酶补充量为433 mg/kg。总之，蛋白酶补充剂从 0 增加到 450 mg/kg 水平提高了鱼的性能，然后随着蛋白酶水平的进一步增加（600-750 mg/kg）而下降。