Effects of Dietary Different Forms of Zinc on Plasma Biochemical Indices,Antioxidant Capacity and Immune Function of Broilers

XUE Mengxiao; WANG Chuanlong; ZHANG Weiyun; ZHANG Liyang; CUI Xiaoyan; LI Tingting; HU Yun; LUO Xugang

doi:10.12418/CJAN2024.256

2024 , Vol. 36 >Issue 5: 2982 - 2991

DOI: https://doi.org/10.12418/CJAN2024.256

RESEARCH PAPER

Effects of Dietary Different Forms of Zinc on Plasma Biochemical Indices,Antioxidant Capacity and Immune Function of Broilers

XUE Mengxiao ^,¹ ,
WANG Chuanlong ² ,
ZHANG Weiyun ¹ ,
ZHANG Liyang ² ,
CUI Xiaoyan ¹ ,
LI Tingting ¹ ,
HU Yun ^,¹^,^* ,
LUO Xugang ^,¹^,^*

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¹ Poultry Mineral Nutrition Laboratory, College of Animal Science and Technology, Yangzhou University, Yangzhou 225009, China
² Mineral Nutrition Research Division, Institute of Animal Science, Chinese Academy of Agricultural Science, Beijing 100193, China

^* HU Yun, associate professor, E-mail: huyun@yzu.edu.cn;

LUO Xugang, professor, E-mail: wlysz@263.net

Received date: 2023-11-23

Online published: 2024-05-15

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Abstract

This experiment was conducted to study the effects of dietary different forms of zinc [inorganic zinc sulfate (ZnSO₄) and zinc proteinate with moderate chelation strength (Zn-Prot M)] on plasma biochemical indices, antioxidant capacity and immune function of broilers. A total of 300 one-day-old male Arbor Acres broilers were fed a semi-purified diet without zinc from 1 to 13 days of age. At 14 days of age, a total of 240 broilers with similar body weight were selected and randomly divided into 3 groups with 8 replicates per group and 10 broilers per replicate according a completely randomized design. Broilers in the control group were fed a basal diet without zinc, and others in experimental groups were fed basal diets supplemented with 60 mg/kg ZnSO₄ and Zn-Prot M (as zinc), respectively. The experiment lasted for 26 days. The results showed as follows: 1) dietary different forms of zinc had no significant effects on the albumin, triglyceride and high-density lipoprotein cholesterol contents and aspartate transaminase (AST) and alanine aminotransferase (ALT) activities in plasma (P>0.05). Compared with the control group, dietary ZnSO₄ and Zn-Prot M significantly decreased the contents of total cholesterol and low-density lipoprotein cholesterol in plasma (P<0.05); compared with the ZnSO₄ group, dietary Zn-Prot M significantly increased the contents of total protein and globulin in plasma (P<0.05), and significantly decreased the low-density lipoprotein cholesterol content and lactate dehydrogenase activity in plasma (P<0.05). 2) Compared with the control group, dietary ZnSO₄ and Zn-Prot M significantly increased the total superoxide dismutase and copper zinc superoxide dismutase activities and total antioxidant capacity in plasma (P<0.05), and significantly decreased the plasma malondialdehyde content (P<0.05); compared with the ZnSO₄ group, dietary Zn-Prot M significantly increased the activities of total superoxide dismutase and copper zinc superoxide dismutase in plasma (P<0.05), and significantly decreased the plasma malondialdehyde content (P<0.05). 3) Dietary different forms of zinc had no significant effects on the contents of interleukin-6, immunoglobulin A and immunoglobulin G in plasma (P>0.05). Compared with the control group, dietary ZnSO₄ and Zn-Prot M significantly decreased the plasma interleukin-1β content (P<0.05); compared with the ZnSO₄ group, dietary Zn-Prot M significantly increased the plasma interleukin-1β content (P<0.05). In conclusion, dietary ZnSO₄ and Zn-Prot M significantly affect some plasma biochemical indices, such as total protein, globulin, total cholesterol and low-density lipoprotein cholesterol contents and lactate dehydrogenase activity, enhance the antioxidant capacity and immune function of broilers, and Zn-Prot M shows better effects than ZnSO₄.

Key words： zinc sources; broilers; plasma biochemical indices; antioxidant capacity; immune function

Cite this article

XUE Mengxiao , WANG Chuanlong , ZHANG Weiyun , ZHANG Liyang , CUI Xiaoyan , LI Tingting , HU Yun , LUO Xugang . Effects of Dietary Different Forms of Zinc on Plasma Biochemical Indices,Antioxidant Capacity and Immune Function of Broilers[J]. Chinese Journal of Animal Nutrition, 2024 , 36(5) : 2982 -2991 . DOI: 10.12418/CJAN2024.256

锌是动物体内300多种酶或者功能蛋白质的必须组分或激活因子,参与多种营养物质的代谢调控活动^[1⇓⇓-4]。饲粮锌缺乏会导致动物生长发育迟缓、免疫功能降低、皮肤屏障功能受损、伤口愈合延迟以及代谢失衡等一系列锌缺乏症^[5-6]。由于饲粮本底锌含量不足以满足畜禽生长发育的需要,故在畜禽饲粮中通常需添加外源锌补充剂^[7⇓-9]。禽类相较于哺乳动物,体温和新陈代谢率更高,更易受到氧化应激的影响。其中,肉鸡生长周期短、代谢速度快,相对于其他动物对锌的需求量更高,因此更容易出现锌缺乏症。在肉鸡生产上,饲粮中主要添加无机硫酸锌(ZnSO₄)或者氧化锌作为锌补充剂来满足家禽的生长需要。但是无机锌的吸收利用率较低,且未被吸收利用的锌随排泄物排出会对环境造成污染^[10-11]。近些年,结构稳定且吸收利用率较高的有机锌越来越多的受到人们的广泛关注^[1,11⇓-13]。课题组前期通过系列试验研究发现,有机锌是否真正优于无机锌,关键取决于锌元素与其有机配位体之间形成键的强度即螯合强度;随着螯合强度的增加,有机锌在肉鸡小肠中的吸收率显著增加,中等螯合强度蛋白锌(zinc proteinate with moderate chelation strength,Zn-Prot M)的靶组织代谢利用最高,因而其生物学利用率最高^[1,11]。然而关于Zn-Prot M的生物学功能尚不清楚。

血浆生化指标的变化能够反映肉仔鸡机体代谢和健康状况,血浆抗氧化指标则能够反映肉仔鸡机体抗氧化能力的整体状况,而血浆免疫指标在一定程度上可以反映机体的整体免疫力。因此,血浆生化、抗氧化以及免疫指标变化可以评估肉仔鸡的生长发育、抗氧化及免疫功能。赵润梅等^[14]研究发现,与ZnSO₄相比,饲粮添加蛋氨酸锌可显著提高血清总蛋白(total protein,TP)和白蛋白(albumin,ALB)含量,改善了机体的蛋白质代谢状况,促进了肉鸡的生长性能。邹田浩^[15]研究发现,与ZnSO₄相比,饲粮添加蛋氨酸锌可以提高肉仔鸡的生长性能、抗氧化能力及免疫功能。然而,杨远廷等^[16]研究发现,饲粮添加甘氨酸锌对肉仔鸡血清常规生化指标无显著影响。赵文昌等^[17]研究表明,饲粮添加蛋氨酸锌对肉仔鸡血清抗氧化指标无显著影响。上述关于有机锌对肉仔鸡生长性能、抗氧化能力及免疫功能的研究结果并不一致。因此,进一步明确有机锌,尤其Zn-Prot M对肉仔鸡血浆生化、抗氧化及免疫指标的影响十分必要。

本试验旨在通过研究饲粮添加不同形态锌(ZnSO₄和Zn-Prot M)对肉仔鸡血浆生化指标、抗氧化能力及免疫功能的影响,为肉鸡生产上开发和应用新型有机锌源饲料添加剂提供科学支撑。

1 材料与方法

1.1 试验材料

ZnSO₄,试剂级,锌含量为22.49%。Zn-Prot M,锌含量为17.09%,螯合强度=51.6。前期研究^[1,11,18-19]已证明Zn-Prot M在肉仔鸡小肠尤其是十二指肠中的吸收率显著高于ZnSO₄,且生物学利用率高。

1.2 试验设计

将300只1日龄爱拔益加(AA)肉仔鸡公雏(购自于江苏京海禽业集团有限公司)于30个不锈钢笼中饲养,每笼10只鸡。在13日龄之前,肉仔鸡饲喂不添加锌的半纯合饲粮,以耗竭其体内锌储存,提高其对锌吸收与利用的灵敏度。14日龄时,从中选取体重接近的240只鸡,采用单因素完全随机试验设计,随机分成3组,每组8个重复,每个重复10只鸡。对照组饲喂不添加锌的玉米-豆粕型基础饲粮,ZnSO₄组在基础饲粮添加60 mg/kg ZnSO₄(以锌计,后同),Zn-Prot M组在基础饲粮添加60 mg/kg Zn-Prot M。不同形态锌添加水平是在前期关于玉米-豆粕型饲粮中肉仔鸡锌需要量的研究^[8]基础上设定。试验期26 d。

参照我国《鸡饲养标准》(NY/T 33—2004)和NRC(1994)家禽营养需要量,配制1~13日龄不加锌的半纯合饲粮(实测锌含量为17.69 mg/kg),14~21日龄和22~39日龄不加锌的玉米-豆粕型基础饲粮(实测锌含量分别为25.72和25.64 mg/kg),并在基础饲粮中分别添加60 mg/kg ZnSO₄(2个阶段饲粮实测锌含量分别为84.91和85.27 mg/kg)和Zn-Prot M(2个阶段饲粮实测锌含量分别为86.93和84.29 mg/kg),配制2种添加不同形态锌的试验饲粮,试验饲粮组成及营养水平见表1。此外,各组饲粮中蛋氨酸和赖氨酸含量通过外源添加人工合成的蛋氨酸和赖氨酸来平衡。

表1 试验饲粮组成及营养水平(饲喂基础)

Table 1 Composition and nutrient levels of experimental diets (as-fed basis) %

项目 Items	半纯合饲粮 (1~13日龄) Semi-purified diet (1 to 13 days of age)	玉米-豆粕型饲粮 (14~21日龄) Corn-soybean meal diet (14 to 21 days of age)	玉米-豆粕型饲粮 (22~39日龄) Corn-soybean meal diet (22 to 39 days of age)
原料Ingredients
玉米Corn		53.82	58.55
豆粕Soybean meal		37.42	32.92
玉米淀粉Corn starch	65.70
酪蛋白Casein	25.75
纤维素Cellulose	3.40
大豆油Soybean oil		4.70	5.00
DL-蛋氨酸DL-Met	0.20	0.30	0.20
磷酸氢钙CaHP $O 4 1)$	1.60	1.87	1.63
碳酸钙CaC $O 3 1)$	1.60	1.14	1.07
氯化钠NaCl¹⁾	0.30	0.30	0.30
预混料Premix²⁾	1.45	0.25	0.18
玉米淀粉+锌Corn starch+Zn³⁾		0.20	0.15
合计Total	100.00	100.00	100.00
营养水平Nutrient levels⁴⁾
代谢能ME/(MJ/kg)	13.14	12.65	12.94
粗蛋白质CP	22.36	21.62	19.93
赖氨酸Lys	1.80	1.12	1.02
蛋氨酸Met	0.86	0.59	0.48
蛋氨酸+胱氨酸Met+Cys	0.96	0.90	0.76
钙Ca	1.02	1.00	0.91
非植酸磷NPP	0.48	0.45	0.40
锌Zn/(mg/kg)	17.69	25.72	25.64

	1)试剂级。Reagent grade.
	2)预混料为每千克饲粮提供 Premix provided the following per kg of diets:1~13日龄 1 to 13 days of age,VA 12 000 IU,VD₃ 4 500 IU,VE 33 IU,VK₃ 3 mg,VB₁ 3 mg,VB₂ 9.6 mg,VB₆ 4.5 mg,VB₁₂ 0.03 mg,泛酸钙 calcium pantothenate 15 mg,烟酸 niacin 54 mg,叶酸 folic acid 1.5 mg,生物素 biotin 0.15 mg,胆碱 choline 700 mg,K (KCl) 3 000 mg,Mg (MgSO₄·7H₂O) 600 mg,Cu (CuSO₄·5H₂O) 8 mg,Mn (MnSO₄·H₂O) 110 mg,Fe (FeSO₄·7H₂O) 40 mg,I [Ca(IO₃)₂·H₂O] 0.35 mg,Se (Na₂SeO₃) 0.15 mg;14~21日龄 14 to 21 days of age,VA 12 000 IU,VD₃ 4 500 IU,VE 33 IU,VK₃ 3 mg,VB₁ 3 mg,VB₂ 9.6 mg,VB₆ 4.5 mg,VB₁₂ 0.03 mg,泛酸钙 calcium pantothenate 15 mg,烟酸 niacin 54 mg,叶酸 folic acid 1.5 mg,生物素 biotin 0.15 mg,胆碱 choline 700 mg,Cu (CuSO₄·5H₂O) 8 mg,Mn (MnSO₄·H₂O) 110 mg,Fe (FeSO₄·7H₂O) 40 mg,I [Ca(IO₃)₂·H₂O] 0.35 mg,Se (Na₂SeO₃) 0.15 mg;22~39日龄 22 to 39 days of age,VA 8 000 IU,VD₃ 3 000 IU,VE 22 IU,VK₃ 2 mg,VB₁ 2 mg,VB₂ 6.4 mg,VB₆ 3 mg,VB₁₂ 0.02 mg,泛酸钙 calcium pantothenate 10 mg,烟酸 niacin 36 mg,叶酸 folic acid 1 mg,生物素 biotin 0.1 mg,胆碱 choline 500 mg,Cu (CuSO₄·5H₂O) 8 mg,Mn (MnSO₄·H₂O) 80 mg,Fe (FeSO₄·7H₂O) 30 mg,I [Ca(IO₃)₂·H₂O] 0.35 mg,Se (Na₂SeO₃) 0.15 mg。
	3)按替代等重的玉米淀粉添加不同形态锌。Different forms of zinc were added in place of equivalent weights of cornstarch.
	4)粗蛋白质、钙和锌为实测值,其他营养水平为计算值。CP, Ca and Zn were measured values, while the other nutrient levels were calculated values.

1.3 饲养管理

鸡笼长×宽×高为90 cm×70 cm×45 cm,每组8个笼,每笼10只鸡,饲养至39日龄。鸡只自由采食和饮用自来水,连续光照。每天观察和记录鸡只死亡数。其他饲养管理按《AA肉仔鸡饲养管理手册》进行。

1.4 样品采集与制备

试验饲粮现配现采,研磨过筛(200目)后低温保存,用于分析其中粗蛋白质、钙和锌含量。采集饮用自来水,用于分析其中锌含量。

于试验鸡39日龄时,采用实验室前期的方法^[1],在鸡只禁食不禁水一夜后,从每个重复选取接近平均体重的3只鸡,使用一次性真空采血管在其肝门静脉汇总处采集5 mL血液,3 500 r/min离心15 min后,收集鸡的血浆并于-20 ℃冻存,用于测定血浆生化、抗氧化及免疫指标,分析前将每个重复3只鸡的血浆样品进行等比例合样处理。

1.5 样品分析

采用凯氏定氮法(GB/T 6432—1994)测定饲料原料及饲粮中粗蛋白质含量。采用5110型等离子体光学发射光谱仪[澳大利亚]测定饲料原料和饲粮中钙含量及饲料原料、饲粮和饮水中锌含量^[20]。饲粮其他营养水平参照《中国饲料成分及营养价值表》(2022年第33版)计算。

采用全自动生化分析仪(7180,日本日立公司)测定血浆中TP、ALB、球蛋白(globulin,GLB)、总胆固醇(total cholesterol,T-CHO)、甘油三酯(triglyceride,TG)、低密度脂蛋白胆固醇(low-density lipoprotein cholesterol,LDL-C)和高密度脂蛋白胆固醇(high-density lipoprotein cholesterol,HDL-C)含量以及谷丙转氨酶(alanine aminotransferase,ALT)、谷草转氨酶(aspartate transaminase,AST)和乳酸脱氢酶(lactic dehydrogenase,LDH)活性。

采用商业试剂盒(南京建成生物工程研究所)测定血浆中总超氧化物歧化酶(total superoxide dismutase,T-SOD;A001-2-1)、铜锌超氧化物歧化酶(copper and zinc superoxide dismutase,CuZn-SOD;A001-2-1)活性和总抗氧化能力(total antioxidant capacity,T-AOC;A015-2-1)以及丙二醛(malonaldehyde,MDA;A003-1-1)含量。

采用酶联免疫分析试剂盒(北京索莱宝科技有限公司)测定血浆中免疫球蛋白A(immunoglobulin A,IgA;SEKCN-0018)、免疫球蛋白G(immunoglobulin G,IgG;SEKCN-0126)、白细胞介素-1β(interleukin-1β,IL-1β;SEKCN-0153)和白细胞介素-6(interleukin-6,IL-6;SEKCN-0161)含量。

1.6 数据统计分析

采用SAS 9.4软件中一般线性模型程序对各项数据进行单因素方差分析,方差分析显著者以最小显著差异法比较平均值间的差异显著性。试验结果以平均值和集合标准误(pooled SE)表示,以P<0.05作为差异显著性检验水平。

2 结果

2.1 饲粮添加不同形态锌对14~39日龄肉仔鸡生长性能和死亡率的影响

饲粮添加ZnSO₄和Zn-Prot M对14~39日龄肉仔鸡平均日增重、平均日采食量、料重比和死亡率均无显著影响^[19]。

2.2 饲粮添加不同形态锌对39日龄肉仔鸡血浆生化指标的影响

由表2可知,饲粮添加不同形态锌对39日龄肉仔鸡血浆中ALB、TG和HDL-C含量以及ALT和AST活性无显著影响(P>0.05),但对血浆中TP、GLB、T-CHO和LDL-C含量以及LDH活性有显著影响(P<0.05)。与对照组相比,饲粮添加ZnSO₄和Zn-Prot M均显著降低了血浆中T-CHO和LDL-C含量(P<0.05);与ZnSO₄组相比,饲粮添加Zn-Prot M显著提高了血浆中TP和GLB含量(P<0.05),显著降低了血浆中LDL-C含量及LDH活性(P<0.05)。血浆中TP和GLB含量及LDH活性在对照组和ZnSO₄组之间无显著差异(P>0.05),血浆中T-CHO含量在ZnSO₄组和Zn-Prot M组之间无显著差异(P>0.05)。

表2 饲粮添加不同形态锌对39日龄肉仔鸡血浆生化指标的影响

Table 2 Effects of dietary different forms of zinc on plasma biochemical indices of broilers at 39 days of age

项目 Items	对照组 Control group	无机硫酸锌组 ZnSO₄ group	中等螯合强度蛋白锌组 Zn-Prot M group	集合标准误 Pooled SE	P值 P-value
总蛋白TP/(g/L)	28.5^b	28.6^b	33.6^a	1.2	0.007 7
白蛋白ALB/(g/L)	11.2	11.5	12.8	0.5	0.123 7
球蛋白GLB/(g/L)	17.5^b	17.0^b	21.0^a	0.9	0.009 3
总胆固醇T-CHO/(mmol/L)	3.31^a	2.32^b	2.60^b	0.14	0.000 3
甘油三酯TG/(mmol/L)	0.76	0.80	0.71	0.05	0.406 5
高密度脂蛋白胆固醇HDL-C/(mmol/L)	1.74	1.82	1.90	0.08	0.433 3
低密度脂蛋白胆固醇LDL-C/(mmol/L)	1.72^a	1.51^b	1.13^c	0.06	<0.000 1
谷丙转氨酶ALT/(U/L)	1.00	1.00	1.50	0.17	0.088 3
谷草转氨酶AST/(U/L)	283	252	263	10	0.116 8
乳酸脱氢酶LDH/(U/L)	746^a	649^a	512^b	37	0.001 4

	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)。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). The same as below.

2.3 饲粮添加不同形态锌对39日龄肉仔鸡血浆抗氧化指标的影响

由表3可知,饲粮添加不同形态锌对39日龄肉仔鸡血浆中CuZn-SOD、T-SOD活性和T-AOC及MDA含量均有显著影响(P<0.05)。与对照组相比,饲粮添加ZnSO₄和Zn-Prot M均显著提高了血浆中T-SOD和CuZn-SOD活性及T-AOC(P<0.05),显著降低了血浆中MDA含量(P<0.05);与ZnSO₄组相比,饲粮添加Zn-Prot M进一步显著提高了血浆中T-SOD和CuZn-SOD活性(P<0.05),显著降低了血浆中MDA含量(P<0.05)。

表3 饲粮添加不同形态锌对39日龄肉仔鸡血浆抗氧化指标的影响

Table 3 Effects of dietary different forms of zinc on plasma antioxidant indices of broilers at 39 days of age

项目 Items	对照组 Control group	无机硫酸锌组 ZnSO₄ group	中等螯合强度蛋白锌组 Zn-Prot M group	集合标准误 Pooled SE	P值 P-value
总抗氧化能力T-AOC/(mmol/L)	0.65^b	0.71^a	0.74^a	0.01	0.000 1
总超氧化物歧化酶T-SOD/(U/mL)	201^c	214^b	229^a	4	0.000 2
铜锌超氧化物歧化酶CuZn-SOD/(U/mL)	137^c	164^b	189^a	5	<0.000 1
丙二醛MDA/(nmol/mL)	10.6^a	8.1^b	4.8^c	0.6	<0.000 1

2.4 饲粮添加不同形态锌对39日龄肉仔鸡血浆免疫指标的影响

由表4可知,饲粮添加不同形态锌对39日龄肉仔鸡血浆中IL-6、IgG和IgA含量均无显著影响(P>0.05),但对血浆中IL-1β含量有显著影响(P<0.05)。与对照组相比,饲粮添加ZnSO₄和Zn-Prot M均显著降低了血浆中IL-1β含量(P<0.05);与ZnSO₄组相比,饲粮添加Zn-Prot M进一步显著降低了血浆中IL-1β含量(P<0.05)。

表4 饲粮添加不同形态锌对39日龄肉仔鸡血浆免疫指标的影响

Table 4 Effects of dietary different forms of zinc on plasma immune indices of broilers at 39 days of age

项目 Items	对照组 Control group	无机硫酸锌组 ZnSO₄ group	中等螯合强度蛋白锌组 Zn-Prot M group	集合标准误 Pooled SE	P值 P-value
白细胞介素-1β IL-1β/(pg/mL)	113^a	94^b	80^c	4	0.000 1
白细胞介素-6 IL-6/(pg/mL)	25.0	22.0	21.9	1.4	0.232 0
免疫球蛋白G IgG/(mg/mL)	4.40	4.29	4.59	0.45	0.894 9
免疫球蛋白A IgA/(μg/mL)	70.4	71.3	71.1	0.4	0.293 5

3 讨论

3.1 饲粮添加不同形态锌对39日龄肉仔鸡血浆生化指标的影响

锌参与动物机体蛋白质、能量以及核酸等物质代谢活动,其代谢产物可通过血浆运输到机体组织器官发挥相应的生理生化功能^[21]。因此,通过检测血浆生化指标可以反映不同形态锌处理下肉仔鸡不同组织器官的生理状态以及对营养物质吸收代谢情况。

血浆TP主要包括ALB、GLB以及纤维蛋白原等。他们在维持血液胶体渗透压、调节血液pH、组成体液免疫以及参与营养物质运输等方面起着重要的调控作用。血浆TP和ALB含量可间接反映动物机体对饲粮蛋白质的消化吸收和代谢情况^[22⇓-24]。而GLB主要由浆细胞和淋巴细胞合成,是反映动物机体免疫功能的重要指标之一。缺锌会造成动物机体血清ALB和GLB含量降低,而适当的补充锌可增加血清中ALB和GLB含量。刘婉盈^[25]研究发现,饲粮添加锌可显著提高肥育猪血清中ALB含量,而对血清中TP含量没有显著影响。赵润梅等^[14]研究发现,锌源和锌水平均没有改变肉鸡血清中TP和ALB含量。而本研究发现,饲粮添加不同形态锌对肉仔鸡血浆ALB含量无显著影响,但对血浆中TP和GLB含量有显著影响;与ZnSO₄组相比,饲粮添加Zn-Prot M显著提高了肉仔鸡血浆中TP和GLB含量,表明Zn-Prot M可促进肉仔鸡机体蛋白质的合成。上述研究结果与前人研究不一致的原因可能与有机锌源的种类、添加剂量以及饲喂时间的不同有关。

血浆中TG、T-CHO、LDL-C和HDL-C含量的变化可反映肝脏TG和胆固醇代谢能力的强弱,血浆中脂质含量越高,说明动物肝脏对脂肪代谢能力越弱,会促进肝脏中脂肪沉积,增加动物患脂肪肝的风险^[23,26]。LDH为含锌离子的金属蛋白,其活性过高可间接反映肝细胞和心肌细胞受损,细胞膜稳定性和完整性受到破坏。ALT和AST活性则是反映肝功能是否正常的重要指标,ALT和AST活性过高,表明肝功能受损。牛现琇^[27]研究发现,不同锌源显著影响了生长肥育猪血清中LDH活性。杨远廷等^[16]研究发现,不同锌源对蛋鸡血清中T-CHO和HDL-C含量及AST和ALT活性无显著影响,但显著影响了血清中TG和LDL-C含量。而本研究发现,饲粮添加不同形态锌均显著降低了肉仔鸡血浆中T-CHO含量;且与ZnSO₄组相比,饲粮添加Zn-Prot M进一步降低了血浆中LDL-C含量和LDH活性,表明饲粮添加ZnSO₄或Zn-Prot M均可改善肉仔鸡的胆固醇代谢,但Zn-Prot M的效果明显优于ZnSO₄。

3.2 饲粮添加不同形态锌对39日龄肉仔鸡血浆抗氧化指标的影响

锌对维持动物机体氧化还原体系的平衡具有重要的调控作用,缺锌则可能诱发机体细胞氧化损伤。抗氧化酶类[超氧化物歧化酶(SOD)、谷胱甘肽过氧化物酶(GSH-Px)等]在动物机体的抗氧化防御体系中发挥着不可替代的作用。SOD是动物维持抗氧化防御体系的主要抗氧化酶,存在着3种SOD的同工酶,其中CuZn-SOD是一种锌依赖性酶,参与组织细胞内氧自由基的清除过程。补锌可以提高CuZn-SOD活性,而缺锌则显著降低CuZn-SOD活性,CuZn-SOD活性的降低会致使组织细胞氧自由基增多,促进机体发生氧化应激反应,诱导细胞损伤和凋亡^[16,28]。胡亮等^[29]研究发现,饲粮添加蛋氨酸锌可显著提高小鼠血清T-SOD活性。吴量等^[30]研究发现,饲粮添加蛋氨酸螯合锌替代硫酸锌显著提高了肉鸡血清CuZn-SOD活性。与前人研究结果相似,本研究发现,饲粮添加不同形态锌均显著提高了肉仔鸡血浆中T-SOD和CuZn-SOD活性;且与ZnSO₄组相比,饲粮添加Zn-Prot M进一步提高了血浆中T-SOD和CuZn-SOD活性。

T-AOC可直接反映机体总体抗氧化水平^[31]。MDA是动物机体内细胞膜上的不饱和脂肪酸被氧自由基攻击后形成的脂质过氧化物。因此,测定机体中MDA含量可反映机体内脂质过氧化程度。胡亮等^[29]研究发现,饲粮添加ZnSO₄和有机蛋氨酸锌均可显著提高小鼠血清中T-AOC,但对MDA含量无显著影响;且与ZnSO₄组相比,蛋氨酸锌进一步提高了小鼠血清中T-AOC。李嘉辉等^[32]研究发现,与ZnSO₄组相比,饲粮添加甘氨酸锌显著降低了肉种鸡血清中MDA含量。与前人研究结果相似,本研究发现,饲粮添加不同形态锌均显著提高了肉仔鸡血浆中T-AOC,显著降低了血浆中MDA含量;且与ZnSO₄组相比,饲粮添加Zn-Prot M进一步显著提高了肉仔鸡血浆T-AOC,显著降低了血浆中MDA含量,表明饲粮添加ZnSO₄和Zn-Prot M均可显著提高肉仔鸡的抗氧化能力,但Zn-Prot M的效果明显优于ZnSO₄。

3.3 饲粮添加不同形态锌对39日龄肉仔鸡血浆免疫指标的影响

先前研究表明,锌对动物机体的免疫功能具有重要的调控作用。锌元素可通过促进T淋巴细胞的成熟,从而提高动物机体的免疫功能,进而对抗病原微生物的入侵^[33]。IL-1β和IL-6是动物机体发生炎症反应过程中的重要炎性因子,其含量异常增高会导致机体免疫功能发生紊乱。IgG和IgA是反映机体免疫功能的重要指标,其含量多少与动物机体的免疫力密切相关。锌可通过提高免疫球蛋白的合成来增强机体免疫功能。陈娟等^[34]研究发现,使用蛋氨酸锌替代硫酸锌可以降低断奶仔猪血清中IL-1β含量。赵文昌等^[17]研究发现,与ZnSO₄组相比,饲粮添加蛋氨酸锌对肉鸡血清中IgG和免疫球蛋白M(IgM)含量无显著影响,但显著降低了肉鸡血清中IL-6含量。与前人研究结果相似,本研究发现,饲粮添加不同形态锌对肉仔鸡血浆中IL-6、IgG和IgA含量无显著影响,但显著降低了血浆中IL-1β含量;且与ZnSO₄组相比,饲粮添加Zn-Prot M进一步显著降低了血浆中IL-1β含量,表明饲粮添加ZnSO₄或Zn-Prot M均可提高肉仔鸡的免疫功能,但Zn-Prot M的效果明显优于ZnSO₄。

4 结论

① 饲粮添加ZnSO₄和Zn-Prot M均可改善肉仔鸡的胆固醇代谢,且Zn-Prot M的效果明显优于ZnSO₄;Zn-Prot M还可改善肉仔鸡的蛋白质代谢。

② 饲粮添加ZnSO₄和Zn-Prot M均可提高肉仔鸡抗氧化能力和免疫功能,且Zn-Prot M的效果明显优于ZnSO₄。

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