Chinese Journal of Animal Nutrition >

2026 , Vol. 38 >Issue 3: 1862 - 1873

DOI: https://doi.org/10.12418/CJAN2026.150

RESEARCH PAPER

Effects of Different Dietary Methionine Levels in Low-Protein Diets on Growth Performance, Carcass Quality, Serum Indices and Methionine Metabolism in Medium-Growing Yellow-Feathered Broilers Aged from 1 to 30 Days

  • HUANG Bing ,
  • LI Zhihang ,
  • XIANG Fengyu ,
  • TAN Dayan ,
  • FAN Xiangqi ,
  • ZHANG Feiran ,
  • LUO Yuheng ,
  • MAO Xiangbing , *
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  • Institute of Animal Nutrition, Sichuan Agricultural University, Chengdu 611130, China
*professor, E-mail:

Received date: 2025-09-02

  Online published: 2026-03-16

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Abstract

This experiment aimed to determine the optimal dietary methionine level in low-protein diet of medium-growing yellow-feathered broilers aged from 1 to 30 days by investigating the effects of corn-miscellaneous meal diets supplemented with different methionine levels on their growth performance, carcass quality, serum indices and methionine metabolism. A total of 720 one-day-old female medium-growing yellow-feathered broiler chicks (Mahuang breed) were randomly allocated into 6 groups with 6 replicates per group and 20 chicks in each replicate. Chicks in control group (NP group) received a diet with crude protein (CP) and amino acid levels meeting the nutrient requirements for medium-growing yellow-feathered broilers aged from 1 to 30 days. The other five groups were the low-protein low-methionine group (LP-Met group), low-protein normal-methionine group (LP group), low-protein high-methionine group 1 (LP+Met1 group), low-protein high-methionine group 2 (LP+Met2 group), and low-protein high-methionine group 3 (LP+Met3 group). Chicks in these five groups were fed low-protein diets with a CP level approximately 2 percentage points lower than that of the NP group [CP level of (19.80±0.07)%], and with dietary methionine levels of 0.37%, 0.45%, 0.54%, 0.63%, and 0.72%, respectively. Other nutrient levels were kept constant. The trial lasted for 30 days. The results showed as follows: 1) compared with NP group, yellow-feathered broilers in LP group showed no significant differences in growth performance, serum immunoglobulin contents, antioxidant indices, free methionine content, or the relative mRNA expression levels of key hepatic methionine metabolism enzymes (P>0.05); LP group had a significantly lower thigh muscle percentage and a significantly higher abdominal fat percentage (P<0.05). 2) The methionine level in low-protein diet significantly affected average daily feed intake and feed-to-gain ratio (F/G) (P<0.05). The F/G showed significant linear and quadratic responses to increasing dietary methionine levels (P<0.05). Using a single-slope broken-line regression analysis with F/G as the evaluation criterion, the optimal dietary methionine level was determined to be 0.55%. 3) The methionine level in the low-protein diet significantly influenced serum immunoglobulin G content, total antioxidant capacity, and glutathione peroxidase activity (P<0.05). Serum free methionine content tended to increase linearly with rising dietary methionine levels (P=0.088). Furthermore, dietary methionine level significantly affected the relative mRNA expression of hepatic glycine N-methyltransferase, S-adenosylhomocysteine hydrolase, methionine synthase, and adenosine deaminase (P<0.05). In conclusion, supplementing an appropriate level of methionine in the low-protein diet for medium-growing yellow-feathered broilers (female Mahuang breed) aged 1 to 30 days can improve growth performance, enhance systemic antioxidant capacity, regulate hepatic methionine metabolism, and optimize methyl-group metabolism and balance. Based on F/G, the optimal dietary methionine level in a corn-miscellaneous meal-based low-protein diet [CP level of (19.80±0.07)%] for these broilers is 0.55%.

Key words： yellow-feathered broilers; low-protein diet; methionine; growth performance; carcass quality; serum indices; methionine metabolism

Cite this article

HUANG Bing , LI Zhihang , XIANG Fengyu , TAN Dayan , FAN Xiangqi , ZHANG Feiran , LUO Yuheng , MAO Xiangbing . Effects of Different Dietary Methionine Levels in Low-Protein Diets on Growth Performance, Carcass Quality, Serum Indices and Methionine Metabolism in Medium-Growing Yellow-Feathered Broilers Aged from 1 to 30 Days[J]. Chinese Journal of Animal Nutrition, 2026 , 38(3) : 1862 -1873 . DOI: 10.12418/CJAN2026.150

当前家禽集约化生产对环境的负面影响日益突出。适当降低饲粮中的粗蛋白质水平并平衡氨基酸组成,可显著减少氮排放,现已成为家禽营养研究热点。豆粕是主要蛋白质源,但鉴于其价格持续攀升且波动频繁、高度依赖进口等问题使得饲料供应的稳定性难以保障[1-2],为解决这一问题,研究者们开始尝试通过其他植物蛋白质源(如棉籽粕、菜籽粕等)部分替代豆粕,并降低饲粮粗蛋白质水平[3-5]。但这种替代策略面临着氨基酸平衡的挑战,尤其是肉鸡蛋氨酸的供给问题。
蛋氨酸不仅是构成蛋白质的重要氨基酸,还是家禽大部分饲粮的第一限制性必需氨基酸,在维持生长性能、胴体品质和抗氧化能力方面起关键作用[6-8]。蛋氨酸不足或过量均会抑制机体的生长与健康[9-11]。因此,确定低蛋白质饲粮中适宜的蛋氨酸水平对保障肉鸡生长、代谢与健康至关重要。
本试验旨在研究玉米-杂粕型低蛋白质饲粮中添加不同水平蛋氨酸对1~30日龄中速型黄羽肉鸡(雌性麻黄鸡)生长性能、胴体品质、血清指标和蛋氨酸代谢的影响,旨在确定黄羽肉鸡玉米-杂粕型低蛋白质饲粮中蛋氨酸的适宜水平,以期为实现节能减排大背景下肉鸡的最佳生长和资源利用效率奠定基础。

1 材料与方法

1.1 伦理声明

动物试验经四川农业大学动物管理与福利委员会批准,批准号:SICAU-2024-116。

1.2 试验动物和试验设计

选取720只体重[(35.09±0.02) g]相近、健康状况良好的1日龄中速型黄羽肉鸡(麻黄鸡)母雏作为试验对象。试验第1天,对所有雏鸡进行称重,根据体重相近原则,随机分为6个组,每组6个重复,每个重复20只鸡。其中,对照组(NP组)饲喂粗蛋白质和氨基酸水平均符合1~30日龄中速型黄羽肉鸡饲养标准的饲粮;其余5个组为低蛋白质低蛋氨酸组(LP-Met组)、低蛋白质正常蛋氨酸组(LP组)、低蛋白质高蛋氨酸1组(LP+Met1组)、低蛋白质高蛋氨酸2组(LP+Met2组)和低蛋白质高蛋氨酸3组(LP+Met3组),均饲喂粗蛋白质水平比NP组降低约2个百分点的低蛋白质饲粮[粗蛋白质水平为(19.80±0.07)%],饲粮中蛋氨酸水平分别为0.37%、0.45%、0.54%、0.63%和0.72%,其他营养水平不变。试验期30 d。

1.3 试验饲粮和饲养管理

饲养试验在四川农业大学动物营养研究所教学科研基地进行。本次试验具体饲养管理和饲粮配制方法均参考本课题组前期试验的方法[12],试验饲粮组成及营养水平见表1。
表1 试验饲粮组成及营养水平(风干基础)

Table 1 Composition and nutrient levels of the experimental diets (air-dry basis)

项目
Items		 组别 Groups
NP LP-Met LP LP+Met1 LP+Met2 LP+Met3
原料 Ingredients
玉米 Corn 43.758 48.550 48.550 48.550 48.550 48.550
小麦 Wheat 13.000 13.000 13.000 13.000 13.000 13.000
玉米胚芽粕 Corn germ meal 4.000 4.000 4.000 4.000 4.000 4.000
豆粕 Soybean meal 22.850 17.460 17.460 17.460 17.460 17.460
棉籽粕 Cottonseed meal 5.000 5.000 5.000 5.000 5.000 5.000
菜籽粕 Rapeseed meal 6.000 6.000 6.000 6.000 6.000 6.000
大豆油 Soybean oil 1.750 1.078 1.078 1.078 1.078 1.078
L-赖氨酸盐酸盐 L-Lys·HCl 0.135 0.315 0.315 0.315 0.315 0.315
L-蛋氨酸 L-Met 0.104 0.042 0.131 0.231 0.331 0.431
L-苏氨酸 L-Thr 0.012 0.100 0.100 0.100 0.100 0.100
L-异亮氨酸 L-Ile 0.098 0.098 0.098 0.098 0.098
氯化钠 NaCl 0.300 0.300 0.300 0.300 0.300 0.300
磷酸氢钙 CaHPO4 1.335 1.550 1.550 1.550 1.550 1.550
石粉 Limestone 1.104 1.855 1.766 1.666 1.566 1.466
乙氧基喹啉 Ethoxyquin (60%) 0.050 0.050 0.050 0.050 0.050 0.050
青蒿粉 Artemisia annua powder 0.120 0.120 0.120 0.120 0.120 0.120
防霉剂 Antifungal agent 0.050 0.050 0.050 0.050 0.050 0.050
植酸酶 Phytase 0.002 0.002 0.002 0.002 0.002 0.002
氯化胆碱 Choline chloride (50%) 0.200 0.200 0.200 0.200 0.200 0.200
维生素预混料 Vitamin premix1) 0.030 0.030 0.030 0.030 0.030 0.030
矿物质预混料 Mineral premix2) 0.200 0.200 0.200 0.200 0.200 0.200
合计 Total 100.000 100.000 100.000 100.000 100.000 100.000
营养水平 Nutrient levels3)
净能 NE/(MJ/kg) 8.47 8.47 8.47 8.47 8.47 8.47
粗蛋白质 CP 21.32 19.80 19.79 19.70 19.80 19.89
赖氨酸 Lys 1.11 1.10 1.12 1.16 1.12 1.15
蛋氨酸 Met 0.44 0.37 0.45 0.54 0.63 0.72
苏氨酸 Thr 0.73 0.73 0.74 0.77 0.76 0.76
异亮氨酸 Ile 0.72 0.76 0.74 0.76 0.75 0.76

1)维生素预混料为每千克饲粮提供 The vitamin premix provided the following per kg of diets:VA 12 000 IU,VD3 3 000 IU,VE 30 mg,VK3 4.8 mg,VB1 3 mg,VB2 9.6 mg,VB6 6 mg,VB12 0.3 mg,烟酸 nicotinic acid 60 mg,泛酸钙 calcium pantothenate 18 mg,叶酸 folic acid 1.5 mg,生物素 biotin 1.8 mg。

2)矿物质预混料为每千克饲粮提供 The mineral premix provided the following per kg of diets:Fe 80 mg,Cu 7 mg,Zn 80 mg,Mn 60 mg,I 0.7 mg,Se 0.15 mg。

3)净能依据《中国饲料成分及营养价值表(2021年第32版)》中各原料对应数值计算得到,其他营养水平均为实测值。NE was calculated on basis of the values of each ingredient in Tables of Feed Composition and Nutritive Values in China (32nd edition, 202l), while nutrient levels of the others were measured values.

1.4 样品采集

本次试验饲粮、血清和胴体样品采集与保存均参考本课题组前期试验的方法[12];肝脏样品的采集:在31日龄时,试验鸡放血处死后,摘取肝脏左侧的第1叶和第2叶的组织块,用生理盐水清洗后速冻于液氮中,并保存于-80 ℃备用。

1.5 指标测定及方法

饲粮常规营养成分水平(粗蛋白质和氨基酸水平)、生长性能指标[平均日增重(average daily gain,ADG)、平均日采食量(average daily feed intake,ADFI)和料重比(feed-to-gain ratio,F/G)]、胴体品质指标(胸肌率、腿肌率和腹脂率)、血清免疫球蛋白指标[免疫球蛋白A(IgA)和免疫球蛋白G(IgG)含量]、血清抗氧化指标[总抗氧化能力(total antioxidant capacity,T-AOC)和谷胱甘肽过氧化物酶(glutathione peroxidase,GSH-Px)活性]的测定均参考本课题组前期试验的方法[12]。
血清游离蛋氨酸含量使用全自动氨基酸分析仪(L-8900,日立公司,日本)进行分析;肝脏蛋氨酸代谢关键酶相关基因的mRNA相对表达量采用荧光定量PCR法,具体步骤参考Luo等[13]的方法进行,测定的相关基因包括磷脂酰乙醇胺N-甲基转移酶(phosphatidylethanolamine N-methyltransferase,PEMT)、甘氨酸N-甲基转移酶(glycine N-methyltransferase,GNMT)、S-腺苷同型半胱氨酸水解酶(S-adenosylhomocysteine hydrolase,SAHH)、甲硫氨酸亚砜还原酶(methionine sulfoxide reductase,MSR)、甲硫氨酸合酶(methionine synthase,MS)和腺苷脱氨酶(adenosine deaminase,ADA),表2是引物序列。
表2 引物序列

Table 2 Primer sequences

基因 Genes 引物序列 Primer sequences (5'—3')
β-肌动蛋白 β-actin F:CCGTGCTGTGTTCCCATCTA
R:TCTGGGCTTCATCACCAACG
磷脂酰乙醇胺N-甲基转移酶 PEMT F:CGGCCTGGATTACAGCGAG
R:TGCTCCCATCTTGCTACCAC
甘氨酸N-甲基转移酶 GNMT F:TGCCAGACTTCAAAGGGGAC
R:GTAGTTGCGGTGGTCGATGA
S-腺苷同型半胱氨酸水解酶 SAHH F:CCATGGGTCACCCTAGCTTC
R:GGCCTGCTTCTCACTCAGTT
甲硫氨酸亚砜还原酶 MSR F:AGGCTGGCTTGCTGAGTTAG
R:CCTGGACCGACCATCACAAA
甲硫氨酸合酶 MS F:TATTGGCGAACGCTGCAATG
R:GAAGGTCCATCCAGCATCCC
腺苷脱氨酶 ADA F:GGGATTTCCGCATCAAAGCC
R:CACCACCTCTGGAGACCAAC

1.6 数据处理和分析

所有试验数据均用Excel 2016进行初步整理,NP组与LP组数据用SAS 9.4软件进行非配对t检验;低蛋白质不同蛋氨酸水平的5个组数据用SAS 9.4软件进行单因素方差分析(one-way ANOVA),并采用Duncan氏法进行组间多重比较,再进一步进行线性及二次回归分析。P<0.05表示差异显著,试验结果数据采用平均值和均值标准误(SEM)表示。
针对中速型黄羽肉鸡氨基酸需要量关键评价指标——生长性能,采用分段回归分析策略,通过SAS 9.4的非线性回归(NLIN)和二次响应面回归(RSREG)过程分别构建单斜率折线模型与二次响应面模型,解析饲粮蛋氨酸水平与生长性能指标间的剂量-效应关系。
单斜率折线模型:
Y=a+b1X,X<R;
Y=a+b1R+b2(X-R),X≥R。
式中:Y为关键评价指标测定值;X为饲粮蛋氨酸水平(%);a为折点前截距;b1为折点前斜率;b2为折点后斜率;R为折点,即蛋氨酸适宜水平(%)。
二次响应面模型:
Y=aX2+bX+c。
式中:Y为关键评价指标测定值;X为饲粮蛋氨酸水平(%);a为二次项系数;b为一次项系数;c为常数项;对称轴X0=-b/2a,即蛋氨酸适宜水平(%)。

2 结果与分析

2.1 不同蛋白质水平饲粮或不同蛋氨酸水平低蛋白质饲粮对黄羽肉鸡生长性能和胴体品质的影响

由表3可知,与NP组相比,LP组黄羽肉鸡的生长性能指标均没有产生显著变化(P>0.05);但LP组腿肌率显著降低(P<0.05),且腹脂率显著升高(P<0.05)。低蛋白质饲粮的蛋氨酸水平对黄羽肉鸡胴体品质指标均未产生显著影响(P>0.05),但显著影响黄羽肉鸡的ADFI和F/G(P<0.05),对ADG未产生显著影响(P>0.05);其中,LP+Met1组ADFI显著低于LP-Met组和LP组(P<0.05);LP-Met组黄羽肉鸡的F/G显著高于其他低蛋白质饲粮组(P<0.05),且F/G随饲粮蛋氨酸水平的提高呈显著的线性和二次曲线变化(P<0.05)。
表3 不同蛋白质水平饲粮或不同蛋氨酸水平低蛋白质饲粮对黄羽肉鸡生长性能和胴体品质的影响

Table 3 Effects of diets with different protein levels or low-protein diets with different Met levels on growth performance and carcass quality in yellow-feather broilers

项目
Items		 组别 Groups 均值标准误
SEM		 P值 P-value
NP LP-Met LP LP+Met1 LP+Met2 LP+Met3 t检验
t test		 方差分析
ANOVA		 线性
Linear		 二次
Quadratic
平均日采食量ADFI/g 43.35 43.14a 43.01a 41.64b 42.40ab 42.05ab 0.184 0.508 0.043 0.027 0.049
平均日增重ADG/g 24.23 23.01 23.95 23.19 23.75 23.43 0.138 0.373 0.162 0.518 0.441
料重比 F/G 1.79 1.88a 1.80b 1.80b 1.79b 1.80b 0.008 0.600 <0.001 0.002 <0.001
胸肌率 Breast muscle Percentage/% 10.49 10.26 10.16 9.79 10.22 10.20 0.122 0.435 0.774 0.950 0.654
腿肌率 Thigh muscle percentage/% 13.39* 12.23 11.41 12.16 12.78 12.36 0.156 0.004 0.097 0.155 0.351
腹脂率Abdominal fat percentage/% 1.31* 1.86 1.70 2.00 1.66 1.47 0.092 0.047 0.458 0.214 0.310

NP组数据肩标“*”表示与LP组相比差异显著(P<0.05)。LP-Met组、LP组、LP+Met1组、LP+Met2组和LP+Met3组之间,同行数据肩标不同字母表示差异显著(P<0.05),相同字母或无字母表示差异不显著(P>0.05)。下表同。

Values in the NP group with “*” superscript represented significant difference compared with the LP group (P<0.05). Among LP-Met, LP, LP+Met1, LP+Met2 and LP+Met3 groups, values in the same row with different letter superscripts mean significant difference (P<0.05), while with the same letter or no letter superscripts mean no significant difference (P>0.05). The same as below.

由表4可知,以F/G为评价指标,进行单斜率折线与二次响应面回归分析得出,饲粮蛋氨酸适宜水平分别为0.55%和0.60%。
表4 低蛋白质饲粮蛋氨酸水平与1~30日龄黄羽肉鸡生长性能回归分析

Table 4 Regression analysis of Met level of low-protein diets with growth performance in yellow-feather broilers aged from 1 to 30 days

项目
Item		 模型
Models		 回归方程
Regression equations		 决定系数
R2		 P值
P-value		 饲粮适宜水平
Dietary optimal
level/%
料重比
F/G		 单斜率折线模型 Y=-0.471X+2.035,X<0.55;
Y=0.119 9X+1.71,X≥0.55		 0.534 <0.001 0.55
二次响应面模型 Y=1.646X2-1.984X+2.376 0.504 <0.001 0.60

2.2 不同蛋白质水平饲粮或不同蛋氨酸水平低蛋白质饲粮对黄羽肉鸡血清免疫球蛋白和抗氧化指标的影响

由表5可知,与NP组相比,LP组黄羽肉鸡的血清免疫球蛋白和抗氧化指标未出现显著变化(P>0.05)。低蛋白质饲粮的蛋氨酸水平对黄羽肉鸡血清IgA含量没有产生显著影响(P>0.05),显著影响血清IgG含量、T-AOC和GSH-Px活性(P<0.05);与LP组相比,LP+Met1组、LP+Met2组和LP+Met3组血清IgG含量显著降低(P<0.05),且IgG含量随饲粮蛋氨酸水平的提高呈显著的线性和二次曲线变化(P<0.05);LP+Met1组血清T-AOC显著高于其他低蛋白质饲粮组(P<0.05),LP+Met2组T-AOC显著高于LP组(P<0.05);LP+Met3组血清GSH-Px活性显著高于其他低蛋白质饲粮组(P<0.05),LP-Met组血清GSH-Px活性显著低于其他低蛋白质饲粮组(P<0.05),且血清GSH-Px活性随饲粮蛋氨酸水平的提高呈显著的线性和二次曲线变化(P<0.05)。
表5 不同蛋白质水平饲粮或不同蛋氨酸水平低蛋白质饲粮对黄羽肉鸡血清指标的影响

Table 5 Effects of diets with different protein levels or low-protein diets with different Met levels on serum indices in yellow-feather broilers

项目
Items		 组别 Groups 均值标准误
SEM		 P值 P-value
NP LP-Met LP LP+Met1 LP+Met2 LP+Met3 t检验
t test		 方差分析
ANOVA		 线性
Linear		 二次
Quadratic
免疫球蛋白A IgA/(μg/mL) 104.40 63.09 162.52 103.82 45.99 109.64 13.989 0.383 0.071 0.789 0.867
免疫球蛋白G IgG/(mg/mL) 1.37 0.86ab 1.06a 0.62bc 0.39c 0.59bc 0.066 0.596 0.008 0.007 0.025
总抗氧化能力 T-AOC/(U/mL) 7.43 9.20bc 6.78c 15.27a 11.56b 9.60bc 0.734 0.779 <0.001 0.252 0.062
谷胱甘肽过氧化物酶 GSH-Px/(U/mL) 4 768 4 223d 5 843c 7 326b 6 418bc 8 439a 315.9 0.074 <0.001 <0.001 <0.001
蛋氨酸Met/(μmol/L) 16.37 15.56 17.43 18.33 19.06 18.35 0.562 0.554 0.400 0.088 0.121

2.3 不同蛋白质水平饲粮或不同蛋氨酸水平低蛋白质饲粮对黄羽肉鸡血清游离蛋氨酸含量和肝脏蛋氨酸代谢关键酶相关基因表达的影响

由表5可知,与NP组相比,LP组黄羽肉鸡血清游离氨基酸含量没有出现显著变化(P>0.05)。虽然不同蛋氨酸水平低蛋白质饲粮组间血清游离蛋氨酸含量差异未达到统计学显著水平,但随着饲粮蛋氨酸水平的提高,血清游离蛋氨酸含量呈线性增加的趋势(P=0.088)。
由表6可知,与NP组相比,LP组黄羽肉鸡肝脏蛋氨酸代谢关键酶相关基因mRNA相对表达量未产生显著变化(P>0.05)。低蛋白质饲粮的蛋氨酸水平显著影响肝脏蛋氨酸代谢关键酶基因GNMT、SAHH、MS和ADA的mRNA相对表达量(P<0.05);LP+Met1组、LP+Met2组和LP+Met3组肝脏GNMT和MS的mRNA相对表达量显著高于LP-Met组和LP组(P<0.05),且LP+Met2组肝脏GNMT的mRNA相对表达量显著高于LP+Met1组和LP+Met3组(P<0.05);LP+Met1组和LP+Met2组肝脏SAHH的mRNA相对表达量显著高于LP-Met组和LP组(P<0.05),且LP+Met3组肝脏SAHH的mRNA相对表达量显著高于LP-Met组(P<0.05);LP+Met2组肝脏ADA的mRNA相对表达量显著高于LP-Met组和LP组(P<0.05),且LP+Met1组肝脏ADA的mRNA相对表达量显著高于LP-Met组(P<0.05);肝脏GNMT、SAHH、MS和ADA的mRNA相对表达量随饲粮蛋氨酸水平的提高呈显著的线性和二次曲线变化(P<0.05);单因素方差分析未检测到不同蛋氨酸水平低蛋白质饲粮组间肝脏MSR的mRNA相对表达量的显著差异(P>0.05),但回归分析表明,饲粮蛋氨酸水平与肝脏MSR的mRNA相对表达量之间存在显著的线性和二次曲线关系(P<0.05)。
表6 不同蛋白质水平饲粮或不同蛋氨酸水平低蛋白质饲粮对黄羽肉鸡肝脏蛋氨酸代谢相关基因表达的影响

Table 6 Effects of diets with different protein levels or low-protein diets with different Met levels on expression of Met-metabolic-related genes in liver of yellow-feather broilers

项目
Items		 组别 Groups 均值标准误
SEM		 P值 P-value
NP LP-Met LP LP+Met1 LP+Met2 LP+Met3 t检验
t test		 方差分析
ANOVA		 线性
Linear		 二次
Quadratic
磷脂酰乙醇胺N-甲基转移酶 PEMT 0.79 0.93 1.00 1.29 2.05 1.19 0.138 0.307 0.050 0.101 0.098
甘氨酸N-甲基转移酶 GNMT 1.26 0.91c 1.00c 1.74b 3.11a 2.06b 0.187 0.285 <0.001 <0.001 <0.001
S-腺苷同型半胱氨酸水解酶 SAHH 1.21 0.84c 1.00bc 2.01a 2.31a 1.70ab 0.162 0.658 0.004 0.004 0.002
甲硫氨酸亚砜还原酶 MSR 0.85 0.90 1.00 1.47 1.60 1.80 0.142 0.429 0.183 0.012 0.044
甲硫氨酸合酶 MS 0.78 1.13b 1.00b 2.58a 2.85a 2.95a 0.221 0.334 <0.001 <0.001 <0.001
腺苷脱氨酶 ADA 1.27 0.92c 1.00bc 1.60ab 1.64a 1.46abc 0.097 0.207 0.031 0.011 0.011

3 讨论

3.1 不同蛋白质水平饲粮和不同蛋氨酸水平低蛋白质饲粮对黄羽肉鸡生长性能的影响

饲粮粗蛋白质水平是影响机体生长发育的关键营养因素,其不仅为机体提供必需氨基酸用于蛋白质合成,还参与多种生理代谢过程[14]。本试验发现,在饲粮粗蛋白质水平约降低2个百分点的情况下,1~30日龄中速型黄羽肉鸡的生长性能未产生显著变化,这一结果与前人的研究结果[15]相似,表明适度降低饲粮粗蛋白质水平不会显著影响肉鸡的生长性能。然而,本试验还发现,低蛋白质饲粮的蛋氨酸水平显著影响黄羽肉鸡ADFI和F/G,且随着饲粮蛋氨酸水平的提高,F/G呈显著的线性和二次曲线变化。这说明饲粮通过平衡必需氨基酸比例(如补充蛋氨酸)可以改善饲料转化效率,提高生长性能。这与前人的研究结果一致,他们进一步分析则认为其源于蛋氨酸通过雷帕霉素靶蛋白(mechanistic target of Rapamycin,mTOR)信号通路调控蛋白质合成[16]。且蛋氨酸作为含硫氨基酸(sulfur-containing amino acid,SAA),其与半胱氨酸(cysteine,Cys)具有协同代谢性,蛋氨酸可通过转硫途径生成Cys[17]。本试验虽未直接测定Cys,但蛋氨酸的积累必然影响总SAA水平。已有研究表明,总SAA水平与蛋白质沉积效率呈正相关[18],这可能解释本试验中补充蛋氨酸虽未显著提升ADG,却显著改善了F/G,即通过优化SAA代谢平衡,提升能量向肌肉组织的分配效率。总SAA还能通过影响家禽皮肤和羽毛健康,调节机体免疫和抗氧化功能来影响生长性能[19-20],这也进一步支撑了本试验的结果。
目前评估氨基酸需求量通常采用单斜率折线方程作为参考指标,且F/G是一个综合反映动物生长性能、饲料转化效率和经济效益的重要指标,其具有很高的代表性和实用价值。本研究发现,以F/G为评价指标,以分段线性回归方程为模型,在玉米-杂粕型低蛋白质饲粮中,1~30日龄中速型黄羽肉鸡的最佳饲粮蛋氨酸水平为0.55%。这一结果高于《黄羽肉鸡营养需要量》(NY/T 3645—2020)和NRC(1994)中推荐的肉鸡蛋氨酸营养需求标准,这可能是因为肉鸡的某种氨基酸需求量可能受到品种、生长阶段、性别及饲粮组成等多种因素的影响[21]。并且,在低蛋白质饲粮中,肉鸡对蛋氨酸需要量可能与正常蛋白质水平下理想氨基酸模式(饲养基准)计算的蛋氨酸需要量不同,桂红兵等[22]研究发现,饲粮粗蛋白质水平降低1.5个百分点时,需补充比常规饲粮高50%的包被赖氨酸以维持日增重。因此,深入研究中速型黄羽肉鸡蛋氨酸需要量,构建动态需求预测模型,为中速型黄羽肉鸡的精准饲粮配制奠定科学基础十分重要。

3.2 不同蛋白质水平饲粮和不同蛋氨酸水平低蛋白质饲粮对黄羽肉鸡胴体品质的影响

胴体品质是评价肉鸡生产性能的重要指标,也是衡量肉品经济价值的关键参数[23]。本试验发现,与NP组相比,LP组1~30日龄中速型黄羽肉鸡的腿肌率显著降低,且腹脂率显著升高,这一结果与前人的研究相一致,即降低饲粮蛋白质水平会导致肉鸡体脂沉积增加,腹脂率升高[24-25];饲喂中高蛋白质饲粮的肉仔鸡胸肌率和腿肌率显著高于饲喂低蛋白质饲粮的肉鸡[26]。这可能是由于较低的饲粮蛋白质水平导致更多的能量被分配到脂肪合成途径,从而影响蛋白质合成的效率和肌肉组织的生长[26-27]。而本试验还发现,低蛋白质饲粮中不同蛋氨酸水平对1~30日龄中速型黄羽肉鸡胸肌率、腿肌率和腹脂率均未产生显著影响。这与Powell等[28]的研究结果一致,可能是因为试验集中于生长前期,胴体组成的显著分化可能在后续育肥阶段才更为明显,其具体情况还需进一步研究进行论证。

3.3 不同蛋白质水平饲粮和不同蛋氨酸水平低蛋白质饲粮对黄羽肉鸡血清免疫球蛋白含量和抗氧化能力的影响

血清免疫球蛋白含量和机体抗氧化能力是评价肉鸡健康状况和代谢功能的重要参数[29]。免疫球蛋白是机体免疫功能的重要组成部分,主要用于识别、中和体内的病原(如细菌、病毒等)[30]。本试验发现,饲粮蛋白质水平降低约2个百分点对1~30日龄中速型黄羽肉鸡血清免疫球蛋白含量均未产生显著影响,这提示,适度降低饲粮粗蛋白质水平可能不会对肉鸡的免疫状态造成负面影响,这一结果与Namroud等[25]的研究结果相似,即在饲粮中补充适宜水平的氨基酸可以维持低蛋白质饲粮条件下肉鸡的正常生理功能。同时,本试验发现,低蛋白质饲粮的蛋氨酸水平对1~30日龄中速型黄羽肉鸡血清IgA含量没有显著影响,但显著影响血清IgG含量,且IgG含量随饲粮蛋氨酸水平的提高呈显著的线性和二次曲线变化;Lai等[31]发现,适量增加饲粮蛋氨酸水平可以提高免疫功能;也有研究发现,饲粮中补充蛋氨酸对肉鸡的免疫反应没有显著影响[32]。以上研究结果的差异可能与动物品种、饲粮组成和免疫应答的复杂调控机制有关。
机体抗氧化系统在维持组织稳态中发挥重要作用,其功能状态可通过血清及组织中的抗氧化指标进行评估[33]。T-AOC体现了体内酶和非酶类抗氧化剂的总体水平,GSH-Px是机体抗氧化系统中重要的组成部分,这些指标可反映机体的氧化还原状态[34-36]。本试验发现,饲粮蛋白质水平降低约2个百分点对血清抗氧化指标没有产生显著影响,这表明适度降低饲粮蛋白质水平对机体的抗氧化能力可能不会造成负面影响,这与吴凡等[37]的研究结果一致。而本试验还发现,低蛋白质饲粮中添加适宜水平的蛋氨酸可以提高1~30日龄中速型黄羽肉鸡血清T-AOC和GSH-Px活性,且血清GSH-Px活性随饲粮蛋氨酸水平的提高呈显著的线性和二次曲线变化,这与前人研究一致[38],这可能是因为蛋氨酸通过转硫途径生成的Cys是谷胱甘肽(glutathione,GSH)合成的限速底物,而GSH又是GSH-Px的关键辅酶[17],蛋氨酸水平的提高促进该反应的进行。

3.4 不同蛋白质水平饲粮和不同蛋氨酸水平低蛋白质饲粮对黄羽肉鸡蛋氨酸代谢的影响

肝脏是蛋氨酸代谢的主要场所,也是蛋白质合成和脂质代谢的重要器官。蛋氨酸被吸收进入肝脏后,代谢合成各种中间产物,对机体蛋白质合成、肝脏脂质代谢、免疫和抗氧化功能起重要调节作用[39-40],而未被肝脏利用的蛋氨酸将被释放进入血液,运输到其他组织利用[41]。本试验发现,适当降低饲粮蛋白质水平对1~30日龄中速型黄羽肉鸡血清游离蛋氨酸含量和肝脏代谢关键酶基因的mRNA相对表达量未产生显著影响,这表明肝脏蛋氨酸代谢具有一定的内稳态调节能力;而低蛋白质饲粮的蛋氨酸水平对黄羽肉鸡肝脏蛋氨酸代谢关键酶基因GNMT、SAHH、MS和ADA的mRNA相对表达量有显著影响。
本试验结果中,当饲粮蛋氨酸水平较低时(LP-Met组),黄羽肉鸡血清游离蛋氨酸含量相对较低;随着饲粮蛋氨酸水平增加,血清游离蛋氨酸含量呈线性上升趋势,这表明低蛋白质饲粮中蛋氨酸水平提高可能使得肝脏对蛋氨酸的吸收和代谢增强,多余的蛋氨酸被释放到血液中。这一结果与万建美[41]的研究结果一致。
在蛋氨酸代谢中,GNMT和PEMT作为甲基转移酶,使S-腺苷蛋氨酸(S-adenosyl methionine,SAM)的甲基转移至多种受体分子(包括DNA、蛋白质和磷脂),产生S-腺苷同型半胱氨酸(S-adenosylhomocysteine,SAH),其被认为是肝脏SAM水平的“安全阀”[42]。SAHH可将甲基转移酶抑制剂SAH水解为同型半胱氨酸和腺苷[43],且ADA可以促进这一作用[39]。同型半胱氨酸可通过MS催化重新生成蛋氨酸,完成蛋氨酸循环[44]。蛋氨酸氧化形成的蛋氨酸亚砜可被MSR还原回蛋氨酸,此过程会消耗活性氧,因此在修复氧化损伤方面发挥关键作用[45]。本试验发现,黄羽肉鸡肝脏GNMT、SAHH、MS、MSR和ADA基因mRNA表达量随低蛋白质饲粮蛋氨酸水平的提高呈显著线性和二次曲线上调。上述结果表明,在低蛋白质饲粮中添加适宜水平的蛋氨酸,能够促进SAH的清除,在维持肝脏蛋氨酸循环活性中发挥了积极作用;能够促进肝脏蛋氨酸再循环,提高蛋氨酸利用效率;并在一定程度上改善了肝脏抗氧化能力。因此,低蛋白质饲粮的适宜蛋氨酸水平可以优化肝脏蛋氨酸代谢,促进甲基代谢和平衡。

4 结论

① 在玉米-杂粕型低蛋白质饲粮[粗蛋白质水平为(19.80±0.07)%]条件下,适宜的蛋氨酸水平能维持1~30日龄中速型黄羽肉鸡(雌性麻黄鸡)的生长性能,且饲粮蛋氨酸适宜水平为0.55%。
② 1~30日龄中速型黄羽肉鸡(雌性麻黄鸡)饲喂玉米-杂粕型低蛋白质饲粮时,添加适宜水平的蛋氨酸能提高机体抗氧化能力,调节肝脏蛋氨酸代谢,优化甲基代谢和平衡。

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