This study investigated the effects of dietary exogenous protease on the growth performance, intestinal health, immune parameters and disease resistance of genetically improved farmed tilapia (GIFT, Oreochromis niloticus). Five test diets with commercial protease at the levels of 0, 1.38, 2.76, 5.52 and 11.04 U/g (named PE0, PE1, PE2, PE5 and PE11, respectively) were administered to triplicate tanks with 30 fish for 60 days, and then, the fish were challenged with Streptococcus agalactiae for 14 days. The results indicated that weight gain increased as exogenous protease increased from 0 to 5.52 U protease/g diet and then decreased significantly (p < .05) with a further increase in exogenous protease supplementation (p < .05). The height of the villi in the proximal intestine and distal intestine, the width of the villi in three segments of the intestine, and the thickness of the muscle layer in the proximal intestine and mid‐intestine (p < .05) were increased in the fish fed the PE5 diet. Immune and antioxidant indices (except malondialdehyde), and survival after challenged with S. agalactiae were higher in fish fed PE5 diets than in those fed other diets (p < .05). In conclusion, 5.52 U/g protease supplementation in a plant‐based diet could promote the growth performance, intestinal physical barrier function, innate immunity and S. agalactiae resistance of GIFT.

中文翻译：

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日粮外源蛋白酶对以植物为基础的日粮喂养的GIFT（尼罗罗非鱼）的生长，肠道健康和免疫的有益作用

这项研究调查了饮食中外源蛋白酶对转基因罗非鱼（GIFT，Oreochromis niloticus）的生长性能，肠道健康，免疫参数和抗病性的影响。将具有商业蛋白酶含量分别为0、1.38、2.76、5.52和11.04 U / g的五种测试日粮（分别命名为PE0，PE1，PE2，PE5和PE11）分别喂入30条鱼的一式三份鱼缸中60天，然后将鱼用无乳链球菌攻击14天。结果表明，体重增加随着外源蛋白酶从0 / 5.5 U / g饮食增加而增加，然后显着降低（p  <.05），而外源蛋白酶补充量进一步增加（p <.05）。在肠道中，近端肠和远端肠的绒毛高度，三段肠的绒毛宽度，近端肠和中肠的肌肉层厚度 均增加（p <.05）。鱼喂食了PE5饮食。饲喂PE5饲料的鱼类的免疫和抗氧化剂指数（丙二醛除外）和无乳链球菌攻击后的存活率高于饲喂其他饲料的鱼类（p  <.05）。总之，在基于植物的饮食中补充5.52 U / g蛋白酶可以促进GIFT的生长性能，肠道物理屏障功能，先天免疫力和无乳链球菌抗性。