胍基乙酸对肉鸡的适用阶段及饲粮蛋氨酸配套强化效果研究

引用本文

赵景鹏, 孙明发, 李培勇, 张俊玲, 杨立彬, 林海. 胍基乙酸对肉鸡的适用阶段及饲粮蛋氨酸配套强化效果研究[J]. 动物营养学报, 2020, 32(2): 691-705.

ZHAO Jingpeng, SUN Mingfa, LI Peiyong, ZHANG Junling, YANG Libin, LIN Hai. Appropriate Period of Guanidinoacetic Acid for Broiler Chickens and Effects of Dietary Methionine Fortification[J]. Chinese Journal of Animal Nutrition, 2020, 32(2): 691-705.

胍基乙酸对肉鸡的适用阶段及饲粮蛋氨酸配套强化效果研究

赵景鹏¹ , 孙明发¹ ^*, 李培勇¹ , 张俊玲² , 杨立彬² , 林海¹

1. 山东农业大学动物科技学院, 山东省动物生物工程与疾病防治重点实验室, 泰安 271018;
2. 北京君德同创农牧科技股份有限公司, 北京 100085

收稿日期: 2019-07-31

基金项目: 国家重点研发计划（2016YFD0500510）；国家自然科学基金（31672442）；山东省"双一流"建设奖补资金；北京君德同创农牧科技股份有限公司委托项目

作者简介: 赵景鹏(1981—), 男, 山东泰安人, 副教授, 博士, 主要从事家禽健康养殖技术研究。E-mail:zjp1299@sdau.edu.cn.

通信作者: 林海, 教授, 博士生导师, E-mail:hailin@sdau.edu.cn.

^*同等贡献作者

摘要: 本研究基于生长性能和肉品质，评价胍基乙酸（GAA）对肉鸡的适用阶段和饲粮蛋氨酸（Met）配套强化效果。选取1日龄雄性爱拔益加肉仔鸡1 920只，随机分为16组，每组设6个重复，每个重复20只鸡。试验分前期（1~21日龄）和后期（22~42日龄）2个饲养阶段，1组为对照组，饲喂常规饲粮（Met水平前期为0.50%，后期为0.40%）。2~6组仅在前期设置Met或GAA处理，其中，2组只把饲粮Met的水平提高至0.65%；3~6组采用双因素完全随机设计，2个饲粮Met水平分别为0.50%和0.65%，2个GAA添加量分别为300和600 mg/kg。7~11组仅在后期设置Met或GAA处理，其中，7组只把饲粮Met水平提高至0.55%；8~11组采用双因素完全随机设计，2个饲粮Met水平分别为0.40%和0.55%，2个GAA添加量分别为400和800 mg/kg。12~16组在全期（1~42日龄）设置Met或GAA处理，前期和后期饲粮设置分别同2~6组和7~11组。试验期42 d。结果发现：1）与对照组相比，只在前期饲喂高剂量GAA并强化Met供应能够显著提高1~21日龄平均日增重和21日龄体重（P < 0.05），显著降低1~21日龄料重比（P < 0.05）；仅在后期饲喂高剂量GAA能够显著提高22~42日龄平均日增重，显著降低22~42日龄料重比（P < 0.05），同时强化Met供应还可显著提高1~42日龄平均日增重及42日龄体重、胸肌指数（P < 0.05），显著降低22~42日龄和1~42日龄料重比及42日龄腹脂指数（P < 0.05）；全期饲喂高剂量GAA能够提高22~42日龄和1~42日龄平均日增重及42日龄体重和胸肌指数（P < 0.05），显著降低22~42日龄和1~42日龄料重比及42日龄腹脂指数（P < 0.05），同时强化Met供应还可显著提高1~21日龄平均日增重和21日龄体重（P < 0.05），显著降低1~21日龄、22~42日龄和1~42日龄料重比（P < 0.05）。2）与对照组相比，全期单独强化饲粮Met或联合添加低剂量GAA可以显著降低42日龄胸肌、腿肌亮度（L^*）值和剪切力（P < 0.05），提高红度（a^*）值和24 h pH（pHu）（P < 0.05）；单独饲喂GAA对肉品质无显著影响（P>0.05）。由此可见，当全程饲喂高剂量GAA时，无需额外补充Met就可使肉鸡终末体重和胴体质量达到最佳；若要阶段性使用GAA，宜在后期高剂量添加且同时补充Met。

关键词: 胍基乙酸蛋氨酸饲养阶段生长性能肉品质肉鸡

Appropriate Period of Guanidinoacetic Acid for Broiler Chickens and Effects of Dietary Methionine Fortification

ZHAO Jingpeng¹ , SUN Mingfa¹ ^*, LI Peiyong¹ , ZHANG Junling² , YANG Libin² , LIN Hai¹

1. Shandong Key Laboratory of Animal Biotechnology and Disease Control, College of Animal Science and Technology, Shandong Agricultural University, Tai'an 271018, China;
2. Beijing Gendone Agricultural Technology Co., Ltd., Beijing 100085, China

Corresponding author: LIN Hai, professor, E-mail: hailin@sdau.edu.cn.

^*Contributed equally

Abstract: A study was conducted to evaluate the appropriate period of guanidinoacetic acid (GAA) for broiler chickens and the effects of dietary methionine (Met) fortification, in terms of growth performance and meat quality. A total of 1 920 one-day-old male Arbor Acres broiler chickens were randomly allotted into 16 groups with 6 replicates per group and 20 birds per replicate. The experiment was divided into starter period (1 to 21 days of age) and later period (22 to 42 days of age). Chickens in group 1 served as the control group, and fed a normal diet (Met level in starter period was 0.50%, and in later period was 0.40%). Groups 2 to 6 were treated with Met or GAA only during the starter period, among them, dietary Met level increased to 0.65% in group 2, a completely randomized design with a 2×2 factorial arrangement was applied to groups 3 to 6, dietary Met levels were 0.50% and 0.65%, and GAA supplementation was 300 and 600 mg/kg. Groups 7 to 11 were treated with Met or GAA only during the later period; among them, dietary Met level increased to 0.55% in group 7, a completely randomized design with a 2×2 factorial arrangement was applied to groups 8 to 11, dietary Met levels were 0.40% and 0.55%, and GAA supplementation was 400 and 800 mg/kg. Groups 12 to 16 were treated with Met or GAA during the whole period (1 to 42 days of age); starter period and later period diets were identical to groups 2 to 6 and groups 7 to 11, respectively. The experiment lasted for 42 days. The results showed as follows:1) compared to the control group, feeding a high dose of GAA plus Met fortification only during the starter period could significantly increase the average daily gain during 1 to 21 days of age and body weight at 21 days of age (P < 0.05), and significantly decreased the ratio of feed to gain during 1 to 21 days of age (P < 0.05); feeding a high dose of GAA only during the later period could significantly increase the average daily gain during 22 to 42 days of age (P < 0.05), and significantly decreased the ratio of feed to gain during 22 to 42 days of age (P < 0.05), and the combination with Met fortification also significantly increased the average daily gain during 1 to 42 days of age and body weight and breast muscle index at 42 days of age (P < 0.05), and significantly decreased the ratio of feed to gain during 22 to 42 days of age and 1 to 42 days of age and abdominal fat index at 42 days of age (P < 0.05); feeding a high dose of GAA during the whole period could significantly increase the average daily gain during 22 to 42 days of age and 1 to 42 days of age and body weight and breast muscle index at 42 days of age (P < 0.05), significantly decreased the ratio of feed to gain during 22 to 42 days of age and 1 to 42 days of age and abdominal fat index at 42 days of age (P < 0.05), and the combination with Met fortification also significantly increased the average daily gain during 1 to 21 days of age and body weight at 21 days of age (P < 0.05), and significantly decreased the ratio of feed to gain during 1 to 21 days of age, 22 to 42 days of age and 1 to 42 days of age (P < 0.05). 2) Compared to the control group, feeding Met fortification alone or in combination with a low dose of GAA during the whole period could significantly decreased the brightness (L^*) value and shear force in breast and thigh muscles at 42 days of age (P < 0.05), significantly increased the redness (a^*) value and 24 h pH (pHu) (P < 0.05); feeding GAA alone had no influence on meat quality(P>0.05). In conclusion, the final body weight and carcass quality can achieve desirable results when broiler chickens are fed a high dose GAA diet throughout the whole period, without need of Met fortification. It is recommended to provide a high dose of GAA plus additional Met in the later period for short-term feeding.

Key words: guanidinoacetic acid methionine feeding period growth performance meat quality broiler chickens

在脊椎动物体内，胍基乙酸(GAA)是肌酸合成的直接前体^[1-2]。在肾脏内，经L-精氨酸-甘氨酸脒基转移酶(AGAT)催化，GAA由L-精氨酸与甘氨酸反应形成^[3]。通过血液循环，GAA被运输到肝脏，在N-甲基转移酶(GAMT)作用下，经甲基化生成肌酸^[4]。借助钠-氯化物依赖性肌酸转运体(CrT)，肌酸被逆浓度梯度摄取进入骨骼肌^[5]。在腺苷二磷酸(ADP)与腺苷三磷酸(ATP)相互转化过程中，肌酸以磷酸肌酸的形式介导高能磷酸基团的转移，参与能量的急性动员与存储。在细胞内，肌酸与磷酸肌酸组成的穿梭系统将高能磷酸基团从线粒体转运到细胞质，在能量的产生和利用之间发挥桥梁作用^[6-7]。每天，体内约有1.7%的肌酸不可避免地被降解为肌酐，随尿液排出^[8]。因此，需要持续供应肌酸，以补偿损耗。

畜禽获取肌酸的途径有2条，要么从头内源合成，要么采食动物性蛋白质源。随着动物性蛋白质源饲料被逐步禁用，饲喂全植物蛋白质型饲粮的畜禽可能每天有约1/2的肌酸需求得不到满足，必须外源补充^[9-10]。相比肌酸，GAA更稳定、更便宜、更适合用作饲料添加剂。它不仅在体内能够转化为肌酸，还可像补充肌酸那样节约饲粮中L-精氨酸^[11]。肉鸡生长发育快，能量需求高，肌酸被视作半必需营养素。大量研究表明，在玉米-豆粕型饲粮中添加GAA可提高肉鸡日增重和胸肉率，降低料重比^[12-13]，但对肉品质无显著影响^[14-15]，甚至有减弱保水性的趋势^[1]，这与在猪上的研究报道^[16]相悖。

GAA向肌酸转化，会消耗大量S-腺苷甲硫氨酸(SAM)，极大程度地增加甲基需求^[17-18]，可能导致高同型半胱氨酸血症或蛋氨酸(Met)缺乏^[19-20]。研究发现，GAA与甲基供体如甜菜碱、胆碱、叶酸或维生素B₁₂联合添加，不影响肌肉肌酸含量和机体能量代谢系统，但降低血液同型半胱氨酸含量，改善Met循环^[20-22]。目前，尚不知直接强化Met供应是否有助于提高GAA对肉鸡生产性能和肉品质的调控效果。肉鸡的生长规律是前期相对增重多，后期绝对增重大^[23]，故在不同饲养阶段，骨骼肌对肌酸的需求可能有所差别。由此提出的问题是，GAA在肉鸡饲粮中是应短期添加(在某一阶段)还是长期添加(养殖全程)？因此，本研究旨在评价GAA对肉鸡的适用阶段和饲粮Met配套强化效果，为家禽合理利用GAA提供新思路。

1 材料与方法 1.1 试验材料

试验用GAA由北京君德同创农牧科技股份有限公司提供，有效成分含量≥98%。饲料级DL-Met购自济南昌诺生物技术有限公司，纯度≥98.5%。

1.2 试验设计

选取体重相近的1日龄雄性爱拔益加(Arbor Acres)肉仔鸡1 920只，随机分为16组，每组6个重复，每个重复20只鸡。试验鸡采用叠层(3层，2重复/层)笼养方式，2笼(1.48 m×0.68 m)为1个重复，每笼饲养10只鸡。试验分前期(1~21日龄)和后期(22~42日龄)2个饲养阶段。1组为对照组，喂以常规饲粮(前期饲粮Met水平为0.50%，后期饲粮Met水平为0.40%，不添加GAA)。2~6组仅在前期设置Met或GAA处理，其中，2组只把饲粮Met水平提高至0.65%(不添加GAA)；3~6组采用双因素完全随机设计，2个饲粮Met水平分别为0.50%和0.65%，2个GAA添加量分别为300和600 mg/kg。7~11组仅在后期设置Met或GAA处理，其中，7组只把饲粮Met水平提高至0.55%(不添加GAA)；8~11组采用双因素完全随机设计，2个饲粮Met水平分别为0.40%和0.55%，2个GAA添加量分别为400和800 mg/kg。12~16组在全期(1~42日龄)设置Met或GAA处理，前期和后期饲粮设置分别同2~6组和7~11组。试验期42 d。试验动物分组见表 1。试验饲粮组成及营养水平见表 2。

表 1 试验动物分组 Table 1 Grouping of experimental animals

项目 Items		胍基乙酸与蛋氨酸组合 Combinations of GAA and Met
		仅前期添加 Supplementation only during starter period						仅后期添加 Supplementation only during later period					全期添加 Supplementation during whole period
		1组(对照) Group 1 (control)	2组 Group 2	3组 Group 3	4组 Group 4	5组 Group 5	6组 Group 6	7组 Group 7	8组 Group 8	9组 Group 9	10组 Group 10	11组 Group 11	12组 Group 12	13组 Group 13	14组 Group 14	15组 Group 15	16组 Group 16
蛋氨酸 Met/%	1~21日龄 1 to 21 days of age	0.50	0.65	0.50	0.50	0.65	0.65	0.50	0.50	0.50	0.50	0.50	0.65	0.50	0.50	0.65	0.65
蛋氨酸 Met/%	22~42日龄 22 to 42 days of age	0.40	0.40	0.40	0.40	0.40	0.40	0.55	0.40	0.40	0.55	0.55	0.55	0.40	0.40	0.55	0.55
胍基乙酸 GAA/(mg/kg)	1~21日龄 1 to 21 days of age			300	600	300	600							300	600	300	600
胍基乙酸 GAA/(mg/kg)	22~42日龄 22 to 42 days of age								400	800	400	800		400	800	400	800

表 1 试验动物分组 Table 1 Grouping of experimental animals

表 2 试验饲粮组成及营养水平(饲喂基础) Table 2 Composition and nutrient levels of experimental diets (as-fed basis)

%
项目 Items	1~21日龄1 to 21 days of age		22~42日龄22 to 42 days of age
项目 Items	0.50% Met	0.65% Met	0.40% Met	0.55% Met
原料Ingredients
玉米Corn (8.5% CP)¹⁾	60.20	60.33	64.59	64.71
豆粕Soybean meal (46% CP)	34.09	33.86	28.95	28.72
豆油Soybean oil	1.56	1.51	2.48	2.43
石粉Limestone	1.04	1.04	1.18	1.18
磷酸氢钙CaHPO₄	2.00	2.00	1.83	1.83
食盐NaCl	0.32	0.32	0.29	0.29
L-赖氨酸盐酸盐L-Lys·HCl (99%)	0.07	0.07	0.10	0.11
DL-蛋氨酸DL-Met (98%)	0.21	0.36	0.13	0.28
氯化胆碱Choline chloride (50%)	0.26	0.26	0.20	0.20
维生素预混料Vitamin premix²⁾	0.05	0.05	0.05	0.05
微量元素预混料Trace mineral premix³⁾	0.20	0.20	0.20	0.20
合计Total	100.00	100.00	100.00	100.00
营养水平Nutrient levels⁴⁾
粗蛋白质CP	21.0	21.0	19.0	19.0
代谢能ME/(MJ/kg)	12.13	12.13	12.55	12.55
钙Ca	0.90	0.90	0.90	0.90
非植酸磷NPP	0.45	0.45	0.42	0.42
赖氨酸Lys	1.15	1.15	1.05	1.05
蛋氨酸Met	0.50	0.65	0.40	0.55
总含硫氨基酸Total sulfur amino acids	0.82	0.97	0.71	0.86
1)胍基乙酸等量替代玉米，添加量为：1~21日龄，0.03%或0.06%；22~42日龄，0.04%或0.08%。Corn was equivalent substituted by GAA, the amount of addition was: 1 to 21 days of age, 0.03% or 0.06%; 22 to 42 days of age, 0.04% or 0.08%. 2)维生素预混料为每千克饲粮提供Vitamin premix provided the following per kg of diets：VA 9 000 IU，VD₃ 2 000 IU，VE 11.0 IU，VK 1.0 mg，VB₁ 1.2 mg，VB₂ 5.8 mg，VB₆ 2.6 mg，VB₁₂ 0.012 mg，烟酸niacin 66.0 mg，泛酸pantothenic acid 10.0 mg，生物素biotin 0.10 mg，叶酸folic acid 0.70 mg。 3)微量元素预混料为每千克饲粮提供Trace mineral premix provided the following per kg of diets：Mg 100 mg，Zn 75 mg，Fe 80 mg，I 0.65 mg，Cu 8.0 mg，Se 0.35 mg。 4)计算值Calculated values。

表 2 试验饲粮组成及营养水平(饲喂基础) Table 2 Composition and nutrient levels of experimental diets (as-fed basis)

1.3 试验动物与饲养管理

试验肉鸡购自山东大宝养殖加工有限责任公司，全程自由采食和饮水，按常规程序免疫接种，舍内温度、相对湿度和光照控制符合白羽肉鸡对环境的要求。

1.4 测定指标与方法 1.4.1 生长性能

在21和42日龄时，以重复为单位，对鸡群进行空腹称重并统计耗料量，以计算平均日采食量、平均日增重和料重比；同时记录死亡和淘汰数，以计算死淘率。

1.4.2 胴体组成

在21和42日龄时，每个重复随机选2只鸡(1只/笼，12只/组)，称重，颈静脉放血处死，取胸肌、腿肌、腹脂、肝脏和肾脏，逐一称重，计算器官指数。

器官指数(%)=100×器官重/体重。

1.4.3 肉品质

在42日龄时，每个重复随机选2只鸡(1只/笼，12只/组)，颈静脉放血处死，胴体置于4 ℃保存。

pH：45 min(pHi)和24 h(pHu)时，在右侧胸肌和腿肌各选择3个位置，用胴体肌肉pH直测仪(pH-STAR型，德国MATTHAUS公司)测定pH，取平均值。

滴水损失：4 h时，在左侧胸肌和腿肌，沿与肌纤维平行和垂直方向，切取2.0 cm×2.0 cm×1.0 cm肉块，称重，悬吊于塑料杯内(与杯壁无接触，肌纤维方向与重力一致)，杯口用保鲜膜密封。于4 ℃放置48 h，再次称重，计算肉样滴水损失。

肉色：24 h时，在右侧胸肌和腿肌各选择3个位置，用色差仪(CR-10型，日本柯尼卡美能达控股公司)测定亮度(L^*)、红度(a^*)和黄度(b^*)，取平均值。

压榨失水率：24 h时，在右侧胸肌和腿肌，切取直径2.523 cm、厚度1.00 cm的圆形肉样。称重后夹在2层纱布间，上下各垫18层定性滤纸，置于YYW-2型应变控制式无侧限压力仪(上海乐傲试验仪器有限公司)平台上，加压至35 kg，保持5 min。再次称重，计算肉样压榨失水率。

蒸煮损失：24 h时，在右侧胸肌和腿肌，切取4.0 cm×2.0 cm×2.0 cm肉块，称重，置于自封袋中(排尽袋内空气)，80 ℃下水浴10 min(保持袋口向上)，冷却，再次称重，计算肉样蒸煮损失。

嫩度：测定蒸煮损失后，用直径1.27 cm的圆形取样器，顺肌纤维方向钻切肉样，分析剪切力(C-LM3型数显式嫩度仪，东北农业大学)。

1.5 统计分析

使用SAS 9.0软件中GLM程序对试验数据进行单因素方差分析(one-way ANOVA)，平均值采用Tukey’s HSD法进行多重比较，P < 0.05表示差异显著。

2 结果 2.1 不同饲养阶段、饲粮蛋氨酸水平下补充胍基乙酸对肉鸡生长性能和胴体组成的影响

如表 3、表 4和表 5所示，无论是在前期、后期还是从全期来看，GAA、Met补充阶段及添加水平对肉鸡平均日采食量均无显著影响(P>0.05)。与对照组相比，只在前期饲喂高剂量GAA并强化Met供应(6组)可以显著提高1~21日龄平均日增重和21日龄体重(P < 0.05)，显著降低1~21日龄料重比(P < 0.05)；仅在后期饲喂高剂量GAA(9组)能够显著提高22~42日龄平均日增重(P < 0.05)，显著降低22~42日龄料重比(P < 0.05)，同时强化Met供应(11组)还可显著提高1~42日龄平均日增重及42日龄体重、胸肌指数(P < 0.05)，显著降低22~42日龄和1~42日龄料重比及42日龄腹脂指数(P < 0.05)；全期饲喂高剂量GAA(14组)能够显著提高22~42日龄和1~42日龄平均日增重及42日龄体重和胸肌指数(P < 0.05)，显著降低22~42日龄和1~42日龄料重比及42日龄腹脂指数(P < 0.05)，同时强化Met供应(16组)还可显著提高1~21日龄平均日增重和21日龄体重(P < 0.05)，显著降低1~21日龄、22~42日龄和1~42日龄料重比(P < 0.05)。仅饲喂低剂量GAA对肉鸡生长性能无显著影响(P>0.05)，但如果全期补充并强化Met供应，可显著降低1~21日龄、22~42日龄和1~42日龄料重比(P < 0.05)。单独强化饲粮Met供应对肉鸡生长性能和胴体组成无显著影响(P>0.05)，前期饲喂GAA或提高饲粮Met水平对21日龄肉鸡胴体组成无显著影响(P>0.05)。

表 3 不同饲养阶段、饲粮蛋氨酸水平下补充胍基乙酸对肉鸡生产性能的影响 Table 3 Effects of GAA supplementation at different rearing periods and dietary Met level on growth performance of broiler chickens

项目 Items		胍基乙酸与蛋氨酸组合Combinations of GAA and Met																集合标准误 Pooled SEM	P值 P-value
		仅前期添加 Supplementation only during starter period						全期添加 Supplementation during whole period					仅后期添加 Supplementation only during later period
		1组(对照) Group 1 (control)	2组 Group 2	3组 Group 3	4组 Group 4	5组 Group 5	6组 Group 6	7组 Group 7	8组 Group 8	9组 Group 9	10组 Group 10	11组 Group 11	12组 Group 12	13组 Group 13	14组 Group 14	15组 Group 15	16组 Group 16
平均日采食量 ADFI/g	1~21日龄 1 to 21 days of age	50.3	49.5	50.1	49.8	49.3	49.0	49.9	50.4	50.0	50.2	50.1	49.4	50.2	49.7	49.2	48.9	1.75	NS
	22~42日龄 22 to 42 days of age	128	127	129	128	127	126	126	128	127	125	124	125	127	126	124	123	7.36	NS
	1~42日龄 1 to 42 days of age	89.2	88.3	89.6	88.9	88.2	87.5	88.0	89.2	88.5	87.6	87.1	87.2	88.6	87.9	86.6	86.0	4.22	NS
平均日增重 ADG/g	1~21日龄 1 to 21 days of age	36.1^cd	35.8^d	35.9^cd	36.4^abcd	36.2^bcd	36.8^ab	35.8^d	36.3^abcd	35.9^cd	36.2^bcd	36.0^cd	35.9^cd	36.1^cd	36.5^abc	36.3^abcd	36.9^a	0.63	0.027
	22~42日龄 22 to 42 days of age	62.3^e	62.2^e	62.4^de	63.0^bcde	62.7^cde	63.4^abcde	62.5^de	62.1^e	64.2^abcd	62.8^cde	64.8^ab	62.7^cde	62.5^de	64.5^abc	63.0^bcde	65.1^a	1.82	0.009
	1~42日龄 1 to 42 days of age	49.2^d	49.0^d	49.2^d	49.7^bcd	49.5^bcd	50.1^abcd	49.2^d	49.2^d	50.1^abcd	49.5^bcd	50.4^abc	49.3^cd	49.3^cd	50.5^ab	49.7^bcd	51.0^a	1.12	0.016
料重比 F/G	1~21日龄 1 to 21 days of age	1.39^a	1.38^ab	1.40^a	1.37^ab	1.36^ab	1.33^b	1.39^a	1.39^a	1.39^a	1.39^a	1.39^a	1.38^ab	1.39^a	1.36^ab	1.36^ab	1.33^b	0.05	0.038
	22~42日龄 22 to 42 days of age	2.05^ab	2.04^abc	2.07^a	2.03^abcd	2.03^abcd	1.99^bcde	2.02^abcd	2.06^a	1.98^cde	1.99^bcde	1.91^fg	1.99^bcde	2.03^abcd	1.95^efg	1.97^def	1.89^g	0.06	0.003
	1~42日龄 1 to 42 days of age	1.81^ab	1.80^abc	1.82^a	1.79^abcd	1.78^abcd	1.75^bcde	1.79^abcd	1.81^ab	1.77^abcd	1.77^abcd	1.73^de	1.77^abcd	1.80^abc	1.74^cde	1.74^cde	1.69^e	0.06	0.022
死淘率 Mortality/%	1~21日龄 1 to 21 days of age	6.67	0	0	0	0	0	6.67	5.00	0	8.33	0	1.67	0	0	0	0	9.87	NS
	22~42日龄 22 to 42 days of age	0	5.00	3.33	0	0	0	0	0	0	0	0	0	1.67	0	0	0	6.73	NS
	1~42日龄 1 to 42 days of age	6.67	5.00	3.33	0	0	0	6.67	5.00	0	8.33	0	1.67	1.67	0	0	0	8.95	NS
同行数据肩标不同小写字母表示差异显著(P < 0.05)，相同或无字母表示差异不显著(P>0.05)，NS表示差异不显著(P>0.05)。下表同。 In the same row, values with different small letter superscripts mean significant difference (P < 0.05), while with the same or no letter superscripts mean no significant difference (P>0.05), NS mean no significant difference (P>0.05). The same as below.

表 4 不同饲养阶段、饲粮蛋氨酸水平下补充胍基乙酸对21日龄肉鸡胴体组成的影响 Table 4 Effects of GAA supplementation at different rearing periods and dietary Met level on carcass composition of 21-day-old broiler chickens

%
项目 Items	胍基乙酸与蛋氨酸组合Combinations of GAA and Met																集合标准误 Pooled SEM	P值 P-value
	仅前期添加 Supplementation only during starter period						仅后期添加 Supplementation only during later period					全期添加 Supplementation during whole period
	1组(对照) Group 1 (control)	2组 Group 2	3组 Group 3	4组 Group 4	5组 Group 5	6组 Group 6	7组 Group 7	8组 Group 8	9组 Group 9	10组 Group 10	11组 Group 11	12组 Group 12	13组 Group 13	14组 Group 14	15组 Group 15	16组 Group 16
体重BW/g	800^cd	794^d	796^cd	806^abcd	802^bcd	815^ab	794^d	804^abcd	796^cd	802^bcd	798^cd	796^cd	800^cd	809^abc	804^abcd	817^a	14.4	0.040
胸肌指数 Breast muscle index	14.0	14.1	14.1	14.2	14.2	14.3	13.9	14.1	13.9	14.1	14.0	14.1	14.0	14.1	14.2	14.2	0.58	NS
腿肌指数 Thigh muscle index	12.7	12.6	12.7	12.6.	12.6	12.5	12.6	12.8	12.6	12.8	12.7	12.7	12.6	12.6	12.5	12.4	0.54	NS
腹脂指数 Abdominal fat index	1.07	1.04	1.08	1.04	1.03	1.02	1.08	1.06	1.05	1.07	1.09	1.05	1.07	1.03	1.02	1.01	0.09	NS
肝脏指数Liver index	2.37	2.42	2.40	2.35	2.38	2.30	2.33	2.41	2.39	2.38	2.35	2.41	2.38	2.34	2.37	2.31	0.14	NS
肾脏指数Kidney index	0.73	0.75	0.72	0.70	0.73	0.72	0.72	0.74	0.72	0.75	0.73	0.74	0.74	0.71	0.73	0.72	0.06	NS

表 5 不同饲养阶段、饲粮蛋氨酸水平下补充胍基乙酸对42日龄肉鸡胴体组成的影响 Table 5 Effects of GAA supplementation at different rearing periods and dietary Met level on carcass composition of 42-day-old broiler chickens

%
项目 Items	胍基乙酸与蛋氨酸组合Combinations of GAA and Met																集合标准误 Pooled SEM	P值 P-value
	仅前期添加 Supplementation only during starter period						仅后期添加 Supplementation only during later period					全期添加 Supplementation during whole period
	1组(对照) Group 1 (control)	2组 Group 2	3组 Group 3	4组 Group 4	5组 Group 5	6组 Group 6	7组 Group 7	8组 Group 8	9组 Group 9	10组 Group 10	11组 Group 11	12组 Group 12	13组 Group 13	14组 Group 14	15组 Group 15	16组 Group 16
体重BW/g	2 108^d	2 100^d	2 105^d	2 126^bcd	2 118^bcd	2 143^abcd	2 107^d	2 110^d	2 146^abcd	2 121^bcd	2 159^abc	2 113^bcd	2 115^bcd	2 163^ab	2 129^bcd	2 184^a	50.5	0.035
胸肌指数 Breast muscle index	18.2^def	18.1^ef	18.0^f	18.3^cdef	18.2^def	18.4^bcdef	18.5^bcdef	18.2^def	18.7^abcde	18.5^bcdef	19.0^ab	18.8^abcd	18.3^cdef	18.9^abc	18.8^abcd	19.2^a	0.62	0.015
腿肌指数 Thigh muscle index	16.0	16.1	16.2	15.9	16.0	15.8	15.8	16.0	15.8	15.9	15.7	15.7	15.9	15.7	15.8	15.6	0.73	NS
腹脂指数 Abdominal fat index	1.35^abc	1.37^a	1.36^ab	1.32^abcde	1.33^abcde	1.30^abcdef	1.32^abcde	1.34^abcd	1.29^bcdef	1.31^abcde	1.26^ef	1.29^bcdef	1.33^abcde	1.27^def	1.28^cdef	1.23^f	0.07	0.035
肝脏指数Liver index	2.15	2.18	2.16	2.13	2.14	2.11	2.12	2.14	2.10	2.11	2.08	2.10	2.13	2.09	2.10	2.07	0.13	NS
肾脏指数Kidney index	0.58	0.60	0.57	0.57	0.59	0.56	0.58	0.57	0.56	0.58	0.55	0.59	0.59	0.56	0.57	0.55	0.07	NS

2.2 不同饲养阶段、饲粮蛋氨酸水平下补充胍基乙酸对肉鸡肉品质的影响

如表 6、表 7所示，GAA、Met补充阶段及添加水平对42日龄肉品质的影响在胸肌和腿肌间相似。与对照组相比，全期单独强化饲粮Met或联合添加低剂量GAA可以显著降低L^*值和剪切力(P < 0.05)，提高a^*值和pHu(P < 0.05)；单独饲喂GAA对肉品质无显著影响(P>0.05)。

表 6 在不同饲养阶段、饲粮蛋氨酸水平下补充胍基乙酸对42日龄肉鸡胸肌品质的影响 Table 6 Effects of GAA supplementation at different rearing periods and dietary Met level on breast meat quality of 42-day-old broiler chickens

项目 Items		胍基乙酸与蛋氨酸组合Combinations of GAA and Met																集合标准误 Pooled SEM	P值 P-value
		仅前期添加 Supplementation only during starter period						仅后期添加 Supplementation only during later period					全期添加 Supplementation during whole period
		1组(对照) Group 1 (control)	2组 Group 2	3组 Group 3	4组 Group 4	5组 Group 5	6组 Group 6	7组 Group 7	8组 Group 8	9组 Group 9	10组 Group 10	11组 Group 11	12组 Group 12	13组 Group 13	14组 Group 14	15组 Group 15	16组 Group 16
肉色 Color	亮度L^*	47.7^ab	47.2^abcd	47.6^abc	48.0^a	47.0^abcd	47.4^abcd	46.6^abcd	47.5^abc	47.9^a	46.4^abcd	46.8^abcd	46.0^cd	47.4^abcd	47.8^ab	45.8^d	46.2^bcd	1.68	0.012
	红度a^*	1.55^cde	1.59^abcde	1.58^abcde	1.54^cde	1.61^abcde	1.57^bcde	1.66^abcde	1.57^bcde	1.53^de	1.68^abcd	1.64^abcede	1.71^ab	1.56^bcde	1.52^e	1.73^a	1.69^abc	0.15	0.029
	黄度b^*	9.22	9.18	9.21	9.25	9.16	9.20	9.13	9.20	9.24	9.11	9.15	9.08	9.19	9.23	9.06	9.10	0.21	NS
pH	pHi	6.29	6.31	6.32	6.28	6.33	6.29	6.34	6.31	6.27	6.36	6.32	6.37	6.30	6.26	6.39	6.35	0.15	NS
pH	pHu	5.86^cde	5.90^abcde	5.89^abcde	5.85^cde	5.92^abcde	5.88^bcde	5.96^abcde	5.88^bcde	5.84^de	5.98^abcd	5.94^abcde	6.01^ab	5.87^bcde	5.83^e	6.03^a	5.99^abc	0.14	0.019
系水力 WHC	压榨失水率PL/%	23.6	23.2	23.5	23.9	23.0	23.4	22.8	23.4	23.8	22.6	23.0	22.1	23.3	23.7	21.9	22.3	2.15	NS
	滴水损失DL/%	2.44	2.41	2.43	2.47	2.39	2.43	2.36	2.42	2.46	2.34	2.38	2.30	2.41	2.45	2.28	2.32	0.21	NS
	蒸煮损失CL/%	22.4	22.1	22.3	22.7	21.9	22.3	21.6	22.2	22.6	21.4	21.8	20.9	22.1	22.5	20.7	21.1	2.10	NS
嫩度 Tenderness	剪切力SF/N	12.5^abc	12.1^abcde	12.4^abcd	12.8^a	11.9^abcde	12.3^abcd	11.5^abcde	12.3^abcd	12.7^ab	11.3^bcde	11.7^abcde	11.0^de	12.2^abcde	12.6^abc	10.8^e	11.2^cde	1.47	0.034

表 7 在不同饲养阶段、饲粮蛋氨酸水平下补充胍基乙酸对42日龄肉鸡腿肌品质的影响 Table 7 Effects of GAA supplementation at different rearing periods and dietary Met level on thigh meat quality of 42-day-old broiler chickens

项目 Items		胍基乙酸与蛋氨酸组合 Combinations of GAA and Met																集合标准误 Pooled SEM	P值 P-value
		仅前期添加 Supplementation only during starter period						仅后期添加 Supplementation only during later period					全期添加 Supplementation during whole period
		1组(对照) Group 1 (control)	2组 Group 2	3组 Group 3	4组 Group 4	5组 Group 5	6组 Group 6	7组 Group 7	8组 Group 8	9组 Group 9	10组 Group 10	11组 Group 11	12组 Group 12	13组 Group 13	14组 Group 14	15组 Group 15	16组 Group 16
肉色 Color	亮度L^*	49.4^ab	49.0^abcd	49.3^abc	49.7^a	48.8^abcd	49.2^abc	48.4^abcd	49.2^abc	49.6^a	48.2^abcd	48.6^abcd	47.8^cd	49.1^abcd	49.5^ab	47.6^d	48.0^bcd	1.57	0.025
	红度a^*	3.22^cd	3.25^abcd	3.25^abcd	3.21^cd	3.27^abcd	3.23^bcd	3.31^abcd	3.24^bcd	3.20^d	3.33^abcd	3.29^abcd	3.37^ab	3.23^bcd	3.19^d	3.39^a	3.35^abc	0.14	0.039
	黄度b^*	8.77	8.73	8.76	8.80	8.71	8.75	8.68	8.75	8.79	8.66	8.70	8.63	8.74	8.78	8.61	8.65	0.21	NS
pH	pHi	6.38	6.40	6.41	6.37	6.42	6.38	6.44	6.40	6.36	6.46	6.42	6.48	6.39	6.35	6.50	6.46	0.17	NS
pH	pHu	6.06^cd	6.10^abcd	6.09^abcd	6.05^cd	6.12^abcd	6.08^bcd	6.16^abcd	6.08^bcd	6.04^d	6.18^abcd	6.14^abcd	6.22^ab	6.07^bcd	6.03^d	6.24^a	6.20^abc	0.15	0.037
系水力 WHC	压榨失水率PL/%	20.5	20.1	20.4	20.8	19.9	20.3	19.7	20.3	20.7	19.5	19.9	19.3	20.2	20.6	19.1	19.5	1.88	NS
	滴水损失DL/%	2.84	2.81	2.83	2.87	2.79	2.83	2.76	2.82	2.86	2.74	2.78	2.71	2.81	2.85	2.69	2.73	0.20	NS
	蒸煮损失CL/%	18.0	17.7	17.9	18.3	17.5	17.9	17.3	17.8	18.2	17.1	17.5	16.9	17.7	18.1	16.7	17.1	1.77	NS
嫩度 Tenderness	剪切力SF/N	13.6^ab	13.3^abcd	13.5^abc	13.9^a	13.1^abcd	13.5^abc	12.7^abcd	13.4^abc	13.8^a	12.5^abcd	12.9^abcd	12.0^cd	13.3^abcd	13.7^ab	11.8^d	12.2^bcd	1.55	0.008

3 讨论

由肌酸和磷酸肌酸组成的ATP再生系统对维持正常的能量代谢至关重要^[6-7]，本试验以玉米、豆粕为主要原料配制全植物蛋白质型饲粮，建立肌酸缺乏模型，评价GAA的饲喂效果。无论是在前期、后期还是全期，单独饲喂低剂量GAA(前期300 mg/kg，后期400 mg/kg)对肉鸡各阶段生长性能和胴体组成均无显著影响。在以往有关GAA的正面报道中，其饲喂剂量多在600~1 200 mg/kg^{[1, 13]}。可是，即使在前期单独饲喂高剂量GAA(600 mg/kg)，本试验也未见各阶段生产性能和胴体组成的改善；而且，在后期单独饲喂高剂量GAA(800 mg/kg)也未像先前报道^[24]的那样提高42日龄胸肌指数，降低腹脂指数。笔者认为，GAA的起效剂量与饲粮能量水平有关。例如，有研究显示，相比低能量水平饲粮(90%科宝公司推荐量)，在高能量水平饲粮(95%和100%科宝公司推荐量)中补充GAA，可提高肉鸡饲料转化效率^[25]。本试验基础饲粮代谢能水平(前期12.13 MJ/kg，后期12.55 MJ/kg)相对较低，可能削弱了肉鸡对GAA的反应敏感性。本试验发现，在后期单独饲喂高剂量GAA可以提高22~42日龄体增重和饲料转化效率，如果全期如此的话，还可提高1~42日龄体增重和42日龄胸肌指数，降低1~42日龄料重比和42日龄腹脂指数。由此提示，GAA最好全程高剂量饲喂，如果选择短期补充的话，在后期添加比在前期更有益。这不仅因为肌肉快速生长需要大量肌酸，还因为磷酸肌酸对心肌具有保护作用^[6-7]。与先前报道^[14-15]一致，在本试验中，单独饲喂GAA对肉品质无显著影响。尽管GAA可通过增加肌酸或磷酸肌酸含量提高直接可用的能量储备，延缓宰后糖酵解^[26]，但是，胍类化合物包括GAA会促进自由基的生成，还降低细胞的非酶抗氧化能力^[27-28]。GAA对能量代谢的积极作用与引发氧化应激的负面效应相抵消，也许是其不影响肉质性状的原因。

Met是家禽玉米-豆粕型饲粮的第一限制性氨基酸，为机体提供活性甲基，参与蛋白质合成代谢^[29-30]。有学者指出，饲粮Met水平较NRC(1994)推荐量增加10%~30%可提高肉鸡平均日增重和胸肌指数，减少腹脂沉积^[31-32]。不过，本试验未见单独强化Met对生长性能和胴体组成的积极影响。这与Wen等^[33]研究结果类似，提示基础饲粮Met水平已能满足肉鸡生长需要。全期单独强化Met提高肌肉pHu，可能与Met降低丙酮酸激酶活性，进而抑制糖酵解和乳酸积累有关^[34]。全期单独强化Met降低肌肉剪切力，说明提高饲粮Met水平能改善嫩度，这可能是由于Met延缓肌肉pH下降速率、维持钙激活中性蛋白酶活性有关^[35]。再者，全期单独强化Met可增加肌肉a^*值，降低L^*值。研究表明，肌肉a^*、L^*值与pHu分别呈正相关和负相关^[36]。本试验未见在前期或后期单独增补Met对肉品质的益处，结合活体和屠体性能指标，适度强化Met对产肉性能影响不大，仅在长期或全程饲喂时对肉质性状有改良作用。

作为SAM的唯一前体，Met在GAA向肌酸转化过程中扮演重要角色。Lemme等^[37]报道，只有当饲粮Met充足时，补充GAA(800 mg/kg)才可提高肉鸡饲料转化效率，暗示Met缺乏会抑制GAA功效(可能通过限制甲基化反应)。本试验进一步证实了这一点，无论在前期、后期还是全期添加，饲粮Met水平与GAA剂量对产肉性能都具有互作效应，提示今后有必要确定两者在各饲养阶段的最适配比。不过，在前期和全期，高剂量GAA与高水平Met联合添加相比前者单独处理的好处仅局限在1~21日龄，并不像在后期饲喂高剂量GAA时，强化Met可提升22~42日龄和1~42日龄生长性能，最终带来42日龄体重和胴体品质的改善。因此，以出栏体重和胴体组成为判据，高水平Met应在后期与高剂量GAA配套。

4 结论

① 对于肉鸡生长性能和胴体组成，GAA的起效剂量前期高于300 mg/kg，后期高于400 mg/kg。

② 基于出栏体重和胴体组成，当全期饲喂高剂量GAA(前期600 mg/kg，后期800 mg/kg)时，无需额外补充Met；当短期添加高剂量GAA时，最好选择在后期且同时强化饲粮Met。

③ 全期单独补充Met对肉品质有益。

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