饲粮蛋氨酸水平对高密度饲养肉鸡生长性能、抗氧化及抗应激能力的影响

【目的】 探讨饲粮蛋氨酸对肉鸡高密度饲养下生长性能、抗氧化和应激反应的影响。【方法】 选取1日龄爱拔益加（AA）肉鸡396只，1~21日龄统一饲喂，于21日龄末选取体重相近的肉鸡随机分为5个处理，每个处理6个重复。对照组肉鸡饲养密度为14只/m²，蛋氨酸水平为0.40%；4个试验组肉鸡饲养密度为20只/m²，饲粮蛋氨酸水平分别为0.35%、0.40%、0.45%和0.50%。试验期21 d，于42日龄采集血浆、肝脏样品，测定应激和抗氧化能力相关指标。【结果】 ①与正常密度组相比，高密度饲养显著降低了42日龄肉鸡体重（BW）、平均日采食量（ADFI）和平均日增重（ADG）（P<0.05），显著提高了肉鸡死亡率（P<0.05）。在高密度饲养情况下：料重比在蛋氨酸水平为0.35%时最高，随着日粮蛋氨酸水平的上升呈线性下降（P<0.05）；与蛋氨酸水平0.35%组相比，0.45%和0.50%蛋氨酸组肉鸡死亡率显著降低（P<0.05）。②与正常密度组相比，高密度饲养组的血浆总抗氧化力（T-AOC）显著降低（P<0.05），而超氧化物歧化酶（SOD）活性、蛋白质羰基（PCO）水平显著上升（P<0.05）。在高密度饲养情况下，血浆PCO水平随着日粮蛋氨酸水平上升呈线性降低（P<0.05）。③与正常密度组相比，高密度饲养显著降低了总蛋白（TP）浓度（P<0.05），提高了谷丙转氨酶（ALT）活性（P<0.05）。在高密度饲养情况下，0.50%蛋氨酸水平组血浆TP水平、谷草转氨酶（AST）活性显著高于0.35%和0.40%蛋氨酸组（P<0.05）；0.35%蛋氨酸组的血浆肌酸激酶（CK）活性显著低于其他组（P<0.05），0.40%和0.45%蛋氨酸组ALT活性显著低于0.35%组（P<0.05）。④与正常密度组相比，高密度饲养显著提高了肝脏中热休克蛋白（HSP70）基因相对表达量（P<0.05）。在高密度饲养情况下，0.35%和0.50%蛋氨酸水平组的HSP70显著高于0.45%水平组（P<0.05）。与正常饲养密度组相比，0.35%和0.50%蛋氨酸组HMG-CoA还原酶（HMGCR）基因相对表达量显著上升（P<0.05）。【结论】 饲养密度与蛋氨酸添加水平对肉鸡的生长性能、应激程度、抗氧化能力均产生了一定影响，高密度饲养可引起肉鸡的应激反应，并对肝功能造成损伤。在高密度饲养条件下，蛋氨酸限制会造成肉鸡死亡率升高，较高蛋氨酸水平也不利于肉鸡肝脏健康。而蛋氨酸水平在0.45%时有较好的抗应激、抗氧化效果，有益于肉鸡生长。

Effects of Dietary Methionine on Growth Performance,Antioxidant Capacity and Stress Tolerance of Broilers Under High-density Feeding

【Objective】 The purpose of this experiment was to explore the effects of dietary methionine on performance, antioxidant and stress responses of broilers under high-stocking density.【Method】 396 1-day-old AA broilers were selected and fed uniformly at the age of 1-21 days.At the end of 21 days, broilers with similar body weights were selected and divided into 5 groups, with 6 replicates in each group.The feeding density of broilers in control group was 14 birds/m², and the methionine level was 0.40%;the test groups were set at 20 birds/m² stocking density, with methionine level at 0.35%, 0.40%, 0.45% and 0.50% in the diet, respectively.At the end of the experiment (42 d), blood and liver samples were collected to measure the stress level and antioxidant capacity.【Result】 ① Compared with normal-density feeding group, high-density rearing significantly reduced the final body weight, average daily feed intake and the average daily body weight gain of broilers during 22-42 days (P<0.05), and significantly increased broiler mortality rate (P<0.05).In the case of high-density feeding, the weight gain ratio of feed consumption was the highest when the methionine level was 0.35%, and it decreased linearly with the increase of the methionine level of the diet (P<0.05).The mortality rate could be reduced by 0.45% and 0.50% methionine diets, compared with 0.35% methionine level (P<0.05).② Compared with normal-density feeding group, T-AOC of high-density feeding group was significantly reduced (P<0.05), while SOD activity and PCO level were significantly increased (P<0.05).In high-density feeding groups, blood PCO level was significantly decreased as methionine level was increasing (P<0.05).③Compared with normal-density feeding group, high-density rearing significantly reduced TP concentration (P<0.05) and increased ALT activity (P<0.05) in plasma.In the case of high-density feeding, the plasma TP concentration and AST activity was significantly higher at 0.50% methionine level than that of the 0.35% and 0.40% methionine groups (P<0.05).The ALT activities of 0.40% and 0.45% methionine groups were significantly lower than that of 0.35% methionine group (P<0.05).④ Compared with normal-density feeding group, high-density rearing significantly increased HSP70 mRNA expression in liver (P<0.05).In the high-density feeding groups, HSP70 was significantly higher in 0.35% and 0.50% methionine groups than 0.45% level group (P<0.05).Compared with normal density feeding group, HMGCR mRNA expression was increased significantly when methionine level was 0.35% and 0.50% (P<0.05).【Conclusion】 The stocking density and the level of methionine addition had a certain impact on broiler's growth performance, stress level, and antioxidant capacity.High-density breeding could cause broiler stress and cause damage to liver function.Under high-density feeding, methionine restriction could increase mortality rate of broilers, and relatively higher methionine also could impair liver health.When methionine level was 0.45%, it had better anti-stress and antioxidant effects, which was beneficial to the growth of broilers.