动物营养学报    2021, Vol. 33 Issue (8): 4730-4739    PDF    
耐镉乳酸菌对镉暴露仔鸡体重、脏器系数和组织中矿物元素含量的影响
蒲俊华1 , 陈大伟1 , 刘茵茵1 , 李惠嘉2 , 陆俊贤1 , 张小燕1 , 唐梦君1 , 唐修君1 , 高玉时1     
1. 江苏省家禽科学研究所, 扬州 225125;
2. 山东农业大学动物科技学院/动物医学院, 泰安 271018
摘要: 本试验旨在探究耐镉乳酸菌对镉暴露仔鸡体重、脏器系数和组织中镉、钙、铁、锌、铜、锰、硒含量影响。选取1日龄如皋黄鸡30只,随机分为3组,每组10个重复,每个重复1只鸡。对照组试验鸡第3~6周灌喂1 mL/(d·只)无菌生理盐水;镉暴露组试验鸡第3~6周灌喂1 mL/(d·只)无菌生理盐水,并在第4~6周饮水中添加5 mg/L镉;镉+耐镉乳酸菌组试验鸡第3~6周灌喂1 mL/(d·只)耐镉乳酸菌液(1×109 CFU/mL),并在第4~6周饮水中添加5 mg/L镉。预试期2周,正试期4周。结果表明:1)各组之间仔鸡体重无显著差异(P>0.05)。2)镉暴露组和镉+耐镉乳酸菌组心脏系数显著低于对照组(P < 0.05),且镉暴露组和镉+耐镉乳酸菌组之间心脏系数无显著差异(P>0.05)。3)镉暴露组的各组织中镉含量显均显著高于对照组(P < 0.05),且各组织中镉含量的高低依次为肾脏>肝脏>脾脏>肺脏>心脏>胸肌。镉+耐镉乳酸菌组的脾脏中镉含量显著低于镉暴露组(P < 0.05)。4)镉+耐镉乳酸菌组肝脏中硒含量显著低于对照组和镉暴露组(P < 0.05)。镉+耐镉乳酸菌组和镉暴露组肾脏中硒含量显著低于对照组(P < 0.05)。镉暴露组肺脏中钙含量显著高于对照组和镉+耐镉乳酸菌组(P < 0.05),镉+耐镉乳酸菌组和镉暴露组肺脏中锌含量显著低于对照组(P < 0.05),镉+耐镉乳酸菌组肺脏中铜含量显著低于对照组(P < 0.05),镉暴露组肺脏中锰含量显著高于对照组和镉+耐镉乳酸菌组(P < 0.05)。镉+耐镉乳酸菌组脾脏中钙和铜含量显著低于对照组和镉暴露组(P < 0.05)。镉暴露组心脏中钙含量显著低于对照组(P < 0.05),镉+耐镉乳酸菌组和镉暴露组心脏中硒含量显著高于对照组(P < 0.05)。由此可见,仔鸡镉暴露时,心脏系数降低,肝脏、肾脏、肺脏、脾脏、心脏和胸肌中镉含量增加,肾脏中硒含量和心脏中钙含量降低;添加耐镉乳酸菌对镉暴露仔鸡心脏系数的降低无改善作用,但降低了脾脏和肝脏中镉含量,并增加了心脏中硒和钙含量。
关键词:     耐镉乳酸菌    仔鸡    脏器系数    矿物元素    
Effects of Cadmium-Tolerant Lactobacillus on Body Weight, Organ Coefficients and Contents of Mineral Elements in Tissues of Cadmium-Exposed Chickens
PU Junhua1 , CHEN Dawei1 , LIU Yinyin1 , LI Huijia2 , LU Junxian1 , ZHANG Xiaoyan1 , TANG Mengjun1 , TANG Xiujun1 , GAO Yushi1     
1. Jiangsu Institute of Poultry Sciences, Yangzhou 225125, China;
2. College of Animal Science and Veterinary Medicine, Shandong Agriculture University, Tai'an 271018, China
Abstract: The aim of this experiment was to study the effects of cadmium (Cd)-tolerant Lactobacillus on body weight, organ coefficients and contents of Cd, calcium (Ca), iron (Fe), zinc (Zn), copper (Cu), manganese (Mn) and selenium (Se) in tissues of Cd-exposed chickens. A total of 30 one-day-old Rugao yellow chickens were randomly divided into 3 groups with 10 replicates per group and 1 chicken per replicate. Chickens in the control group were fed 1 mL/(d·bird) of sterile physiological saline via gavage from the 3rd week to the 6th week; chickens in the Cd-exposed group were fed 1 mL/(d·bird) of sterile physiological saline via gavage from the 3rd week to the 6th week, and were given drinking water with 5 mg/L Cd from the 4th week to the 6th week; chickens in the Cd+Cd-tolerant Lactobacillus group were fed 1 mL/(d bird) of Cd-tolerant Lactobacillus liquid (1×109 CFU/mL) via gavage from the 3rd week to the 6th week, and were given drinking water with 5 mg/L Cd from the 4th week to the 6th week. The experimental period was 6 weeks, including 2 weeks of preliminary trial period and 4 weeks of trial period. The results showed as follows: 1) there was no significant difference in body weight of chickens among all groups (P>0.05). 2) The heart coefficient of the Cd-exposed group and the Cd+Cd-tolerant Lactobacillus group was significantly lower than that of the control group (P < 0.05), and there was no significant difference in the heart coefficient between the Cd-exposed group and the Cd+Cd-tolerant Lactobacillus group (P>0.05). 3) The contents of Cd in all tissues of the Cd-exposed group were significantly higher than those of the control group (P < 0.05), and the contents of Cd in tissues from high to low were kidney>liver>spleen>lung>heart>breast muscle. The spleen Cd content of the Cd+Cd-tolerant Lactobacillus group was significantly lower than that of the Cd-exposed group (P < 0.05). 4) The liver Se content of the Cd+Cd-tolerant Lactobacillus group was significantly lower than that of the control group and the Cd-exposed group (P < 0.05). The kidney Se content of the Cd+Cd-tolerant Lactobacillus group and the Cd-exposed group was significantly lower than that of the control group (P < 0.05). The lung Ca content of the Cd-exposed group was significantly higher than that of the control group and the Cd+Cd-tolerant Lactobacillus group (P < 0.05), the lung Zn content of the Cd+Cd-tolerant Lactobacillus group and Cd-exposed group was significantly lower than that of the control group (P < 0.05). The lung Cu content of the Cd+Cd-tolerant Lactobacillus group was significantly lower than that of the control group (P < 0.05), and the lung Mn content of the Cd-exposed group was significantly higher than that of the control group and the Cd+Cd-tolerant Lactobacillus group (P < 0.05). The contents of Ca and Cu in spleen of the Cd+Cd-tolerant Lactobacillus group were significantly lower than those of the control group and Cd-exposed group (P < 0.05). The heart Ca content of the Cd-exposed group was significantly lower than that of the control group (P < 0.05), and the heart Se content of the Cd+Cd-tolerant Lactobacillus group and Cd-exposed group was significantly higher than that of the control group (P < 0.05). Thus, when the chickens are exposed to Cd, the heart coefficient decreases, the contents of Cd in liver, kidney, lung, spleen, heart and breast muscle increase, and the kidney Se content and heart Ca content decrease. The supplementation of Cd-tolerant Lactobacillus has no significant effect on ameliorating heart coefficient, but it reduces the spleen and liver Cd content, and increases the contents of Se and Ca in heart.
Key words: Cd    Cd-tolerant Lactobacillus    chickens    organ coefficients    mineral elements    

近几十年来,随着冶金、电池等工业的快速发展,环境中重金属包括镉的污染加剧[1]。镉可在土壤、水体等环境中长期存在,并可随生物链迁移至植物、动物和人体中[2],在组织中蓄积,半衰期长达25~30年[3]。镉可对机体的大脑、肝脏、肾脏等重要器官造成严重损伤[4-5],著名的痛痛病就是由镉引起的[6]。镉因其较强的毒性而被国际癌症分类研究机构(international agency for research on cancer classification,IARC)列为Ⅰ类致癌物[7]

鉴于镉的严重危害性,我国《饲料卫生标准》(GB 13078—2017)中对镉的含量范围做出了限定(≤0.5 mg/kg)。相关的研究调查表明,农业土壤中镉的超标率较高,饲料包括饲料原料、预混料、全价配合饲料等均存在有镉超标的情况[8-10]。许多研究已证实镉可造成家禽生产性能的下降,损害家禽机体,同时禽产品内残留的镉会对人体造成潜在的食品安全隐患[11-13]。针对此种状况,采取相应的措施防控家禽生产中重金属镉的污染是家禽养殖业健康发展的趋势。目前已有研究报道,利用微生物对重金属的吸附性来减除人和动物体内的重金属。如Zhai等[14-15]发现,志愿者服用8周的益生菌后,植物乳杆菌CCFM8610显著降低志愿者血液镉含量,而动物试验表明植物乳杆菌CCFM8610抑制镉在小鼠体内的吸收,显著促进粪便中镉的排出,显著降低组织中镉含量。Dubey等[16]报道,益生菌戊糖片球菌(Pediococcus pentosaceus)GS4可通过粪便排出镉,减少镉在小鼠组织的沉积,从而减轻镉的毒性,保护肝脏和肠道。目前筛选具有抗镉性能的益生菌在小鼠上的研究应用相对较多,但在家禽养殖上的研究应用很少见。在本研究的前期工作中,筛选出了1株耐镉乳酸菌,添加于蛋鸡饲粮中提高了蛋鸡的生产性能,显著改善了镉暴露导致的蛋鸡脾脏萎缩,同时显著降低了心脏镉的残留量[17-18]。因此,本研究进一步探究耐镉乳酸菌对镉暴露仔鸡的体重、脏器系数、组织镉和矿物元素(钙、铁、锌、铜、锰、硒)含量的影响,为将其开发应用于家禽生产中提供理论基础。

1 材料与方法 1.1 耐镉乳酸菌

试验采用的耐镉乳酸菌从鸡肠道分离出,经分子生物学方法鉴定为约氏乳杆菌,命名为约氏乳杆菌Cd3-1,采用液体乳酸细菌培养基(MRS)于37 ℃厌氧培养18 h后,用无菌生理盐水将其稀释为1×109 CFU/mL的菌液备用。

1.2 试验设计

选取健康活泼、体重均一的1日龄如皋黄鸡30只,随机分为3组,每组10个重复,每个重复1只鸡。预试期2周,正试期4周。基础饲粮参考我国《鸡饲养标准》(NY/T 33—2004)配制,基础饲粮组成及营养水平见表 1。基础饲粮中镉含量实测值为0.066 mg/kg。预试期第1周饲喂含抗生素(那西肽,饲粮中添加量为2.5 mg/kg,以降低雏鸡早期肠道的不利影响)的基础饲粮,预试期第2周及正试期饲喂无抗生素的基础饲粮。对照组试验鸡第3~6周灌喂1 mL/(d·只)无菌生理盐水;镉暴露组试验鸡第3~6周灌喂1 mL/(d·只)无菌生理盐水,并在第4~6周饮水中添加5 mg/L镉;镉+耐镉乳酸菌组试验鸡第3~6周灌喂1 mL/(d·只)耐镉乳酸菌液(1×109 CFU/mL),并在第4~6周饮水中添加5 mg/L镉。饮水中镉以氯化镉(CdCl2,纯度≥99.99%,赛默飞世尔科技公司,美国,货号:100228375)形式添加,具体操作为称取0.407 7 g的CdCl2溶解于超纯水中并定容于50 mL容量管,配制成镉浓度为5 g/L的母液,使用时用超纯水稀释为镉浓度为5 mg/L的试验鸡饮用水。试验在江苏省家禽科学研究所动物试验鸡舍开展,3组试验鸡带不同颜色翅号,同组试验鸡同笼饲养。常规饲养管理,自由采食和饮水。

表 1 基础饲粮组成及营养水平(风干基础) Table 1 Composition and nutrient levels of the basal diet (air-dry basis)  
1.3 样品采集及指标测定

生产性能:观测记录正试期各组试验鸡生长状况和死淘情况,称量并记录各组全部试验鸡每周末体重。

样品采集:待第6周末各组试验鸡全群称过体重后,屠宰后取胸肌及内脏组织(肝脏、肾脏、肺脏、脾脏、心脏),并称量内脏组织。各样品冻存于-20 ℃,备测。

脏器系数按以下公式计算:

脏器系数(%)=(脏器重/活体重)×100。

镉、钙、铁、锌、铜、锰、硒含量的测定:各组织样品分别取0.6 g,加5 mL硝酸(优级纯,中国医药集团有限公司)和1 mL 30%双氧水(分析纯,中国医药集团有限公司),微波消解仪(MARS,美国CEM公司)消解,赶酸仪(bhw-09c20,培安有限公司)140 ℃赶酸至溶液剩余0.5 mL,超纯水转移定容至25 mL容量瓶,上机测定各元素含量。其中铁、锌、钙含量用原子吸收分光光度计(AA800,美国珀金埃尔默股份有限公司)测定,铜、锰、硒及镉含量用电感耦合等离子质谱仪(ICP-MS,XSERIES 2,美国赛默飞世尔科技公司)测定。

1.4 数据分析

采用Excel 2019整理数据,采用SPSS 16.0统计软件进行单因素方差分析(one-way ANOVA),LSD法进行多重比较,以P<0.05作为差异显著性判断标准,结果以平均值±标准误表示。

2 结果 2.1 耐镉乳酸菌对镉暴露仔鸡体重的影响

整个正试期,各组试验鸡精神状态良好,各组均无死淘鸡。如表 2所示,镉暴露组仔鸡体重与对照组无显著差异(P>0.05),镉+耐镉乳酸菌组仔鸡体重与对照组也无显著差异(P>0.05)。

表 2 耐镉乳酸菌对镉暴露仔鸡体重的影响 Table 2 Effects of Cd-tolerant Lactobacillus on weight of Cd-exposed chickens (n=10)  
2.2 耐镉乳酸菌对镉暴露仔鸡脏器系数的影响

表 3可知,各组之间肝脏、肾脏、肺脏和脾脏系数均无显著差异(P>0.05)。镉暴露组和镉+耐镉乳酸菌组心脏系数显著低于对照组(P<0.05),且镉暴露组和镉+耐镉乳酸菌组之间心脏系数无显著差异(P>0.05)。

表 3 耐镉乳酸菌对镉暴露仔鸡脏器系数的影响 Table 3 Effects of Cd-tolerant Lactobacillus on organ coefficients of Cd-exposed chickens (n=10)  
2.3 耐镉乳酸菌对镉暴露仔鸡组织中镉含量的影响

表 4可知,镉暴露组的各组织中镉含量显均显著高于对照组(P<0.05),且各组织中镉含量的高低依次为肾脏>肝脏>脾脏>肺脏>心脏>胸肌。镉+耐镉乳酸菌组的各组织中镉含量均低于镉暴露组,其中镉+耐镉乳酸菌组的肝脏、肾脏、脾脏中镉含量较镉暴露组分别下降了31.6%(P>0.05),14.5%(P>0.05)和39.8%(P<0.05)。镉+耐镉乳酸菌组的肺脏、心脏和胸肌中镉含量与镉暴露组和对照组差异不显著(P>0.05)。

表 4 耐镉乳酸菌对镉暴露仔鸡组织中镉含量的影响 Table 4 Effects of Cd-tolerant Lactobacillus on tissue Cd content of Cd-exposed chickens (n=10)  
2.4 耐镉乳酸菌对镉暴露仔鸡组织中钙、铁、锌、铜、锰和硒含量的影响

表 5可知,各组之间肝脏中钙、铁、锌、铜和锰含量无显著差异(P>0.05)。镉+耐镉乳酸菌组肝脏中硒含量显著低于对照组和镉暴露组(P<0.05)。

表 5 耐镉乳酸菌对镉暴露仔鸡组织中钙、铁、锌、铜、锰和硒含量的影响 Table 5 Effects of Cd-tolerant Lactobacillus on contents of Ca, Fe, Zn, Cu, Mn and Se in tissues of Cd-exposed chickens (n=10)  

各组之间肾脏中钙、铁、锌、铜和锰含量无显著差异(P>0.05)。镉+耐镉乳酸菌组和镉暴露组肾脏中硒含量显著低于对照组(P<0.05)。

各组之间肺脏中铁和硒含量无显著差异(P>0.05)。镉暴露组肺脏中钙含量显著高于对照组和镉+耐镉乳酸菌组(P<0.05),而镉+耐镉乳酸菌组和对照组之间肺脏中钙含量无显著差异(P>0.05)。镉+耐镉乳酸菌组和镉暴露组肺脏中锌含量显著低于对照组(P<0.05)。镉+耐镉乳酸菌组肺脏中铜含量显著低于对照组(P<0.05)。镉暴露组肺脏中锰含量显著高于对照组和镉+耐镉乳酸菌组(P<0.05)。

各组之间脾脏中铁、锌、锰和硒含量无显著差异(P>0.05)。镉+耐镉乳酸菌组脾脏中钙和铜含量显著低于对照组和镉暴露组(P<0.05)。

各组之间心脏中铁、锌、铜和锰含量无显著差异(P>0.05)。镉暴露组心脏中钙含量显著低于对照组(P<0.05),镉+耐镉乳酸菌组心脏中钙含量与对照组无显著差异(P>0.05)。镉+耐镉乳酸菌组和镉暴露组心脏中硒含量显著高于对照组(P<0.05)。

各组之间胸肌中钙、铁、锌、铜、锰和硒含量无显著差异(P>0.05)。

3 讨论 3.1 耐镉乳酸菌对镉暴露仔鸡体重的影响

研究表明,镉对动物的生产性能的影响与其剂量相关。Abou-Kassem等[19]研究发现,随着饲粮中镉水平的增加,鹌鹑的活体重和体增重线性下降,当饲粮中镉水平增至120 mg/kg时,鹌鹑的死亡率线性增加,胴体率线性下降。Tao等[20]报道,蛋鸡饲粮中镉水平达到60 mg/kg时,产蛋量和料蛋比显著下降。Erdogan等[21]指出,肉鸡饮用含25 mg/L镉的水6周,肉鸡体重、体增重和饲料效率显著降低。本试验中,镉暴露对仔鸡的体重并无显著影响,这可能与本试验中镉的暴露剂量较低(5 mg/L)有关。当动物的生产性能受到镉的影响,补加益生菌可以降低镉的危害,改善动物的生产性能。如当罗非鱼生活环境中含有3.2 mg/L的镉时,其饲料中补充嗜酸乳酸杆菌(1×1010 CFU/kg)则将其存活率从75.2%提升至91.6%[22]。而尼罗河罗非鱼饲料中镉水平达到50 mg/kg时,其体重和体增重极显著降低,补加1 g/kg Bactocell®(乳酸菌的副产物,含1×1010 CFU/kg乳酸片球菌)显著提高了体增重和饲料转化率[23]。本研究中,补加耐镉乳酸菌对仔鸡体重无显著影响,可能与镉的暴露剂量和补加的耐镉乳酸菌剂量相关。

3.2 耐镉乳酸菌对镉暴露仔鸡脏器系数的影响

在动物试验中,尤其是在一些毒理学试验中,脏器系数是重要的观测指标。一方面脏器系数的变化可反映出毒性物质对脏器的综合毒性作用,当脏器发生退行性萎缩或充血、水肿等增大变化,其脏器系数会发生相应的改变;另一方面,脏器系数发生了改变的脏器可为寻找毒物作用的靶器官提供重要线索[24]。重金属镉作为一种毒性物质,当其从外界进入动物机体并在其体内蓄积时,会对动物的脏器造成损伤,致其脏器系数产生变化。汪纪仓等[25]研究表明,腹腔注射镉溶液致大鼠肝脏和肾脏系数显著增加,而睾丸系数显著降低。曹琼洁等[26]研究发现,高剂量氯化镉导致小鼠肝脏系数显著升高,而低剂量氯化镉导致肾脏系数显著升高。本试验中,仔鸡镉暴露后,心脏系数显著降低,而补加耐镉乳酸菌未改善心脏系数的降低。有研究报道,镉显著降低产蛋鸡的脾脏系数,补加耐镉乳酸菌则使脾脏系数恢复正常[18]。研究结果的不同说明镉对处于不同生理期鸡的脏器影响程度不同,而补加的耐镉乳酸菌对镉暴露鸡的脏器产生的保护作用效果不同。

3.3 耐镉乳酸菌对镉暴露仔鸡组织中镉含量的影响

肾脏和肝脏是动物机体代谢的重要组织,也是镉毒性作用的最主要靶器官[4]。本试验结果表明,仔鸡镉暴露后,各组织中镉含量量均显著高于对照组,而肾脏和肝脏中镉含量远高于其他组织。补加耐镉乳酸菌显著降低了脾脏中镉含量,且肝脏中镉含量亦著减少的趋势。另有研究表明,耐镉乳酸菌显著减少镉暴露蛋鸡的心脏中镉含量,其他组织中镉含量也呈降低趋势,且随耐镉乳酸菌剂量的增加,镉含量消减趋势也更明显[18]。Jafarpour等[27]研究发现,凝结芽孢杆菌和植物乳杆菌CNR273可以抵抗小鼠急性镉毒性,降低肝脏和肾脏中镉含量。有研究指出,益生菌可能通过细胞壁和细胞膜与镉结合,促进镉在粪中的排出,从而降低肝肾中镉含量[28]。Zhai等[15]研究认为,植物乳杆菌CCFM8610减少小鼠肝脏中镉含量的原因在于植物乳杆菌CCFM8610通过肠肝循环促进镉在肠道的排出。

大部分口服方式处理的镉通过粪便排泄[28],而吸收进入体内的镉有50%~70%通过血液运输至肾脏和肝脏沉积。Djurasevice等[29]试验发现,大鼠镉暴露同时补加嗜酸乳酸杆菌Rosell-11、嗜酸乳酸杆菌Rosell-52与长双歧杆菌(Bifidobacterium longum)Rosell-175混合菌后,粪便中镉含量增加,组织和血液中镉含量下降,且三者间存在强相关性,表明益生菌通过粪便加速镉的排出。此外,戊糖片球菌GS4[16]以及嗜酸乳酸杆菌[30]对小鼠的试验结果均表明,益生菌的使用使试验动物粪便中镉含量增加,而组织中镉含量下降。综合这些研究结果表明,益生菌通过与镉结合促进镉在粪便中的排出是减少镉在组织中沉积的主要机制。

耐镉益生菌对动物体内镉的去除能力与其对镉吸附能力的强弱相关,不同的菌株吸附镉的差异性较大。Bhakta等[31]从环境样品中筛选出5株抗镉的乳酸菌,其中1株为罗伊氏乳杆菌(Lactobacillus reuteri)Cd70-13,其镉去除率最高,达到25%,并表现出在鱼肠道中高存活率和高吸收镉的潜力。与普通的益生菌相比,耐镉益生菌发挥其吸附镉的优势还在于其对镉的高耐受性。当益生菌能耐受镉的最小抑制浓度(minimum inhibitory concentration,MIC)超过100 mg/L时,则认为其对镉有耐受性[32]。Zhai等[33]研究表明,与低耐受镉的植物乳杆菌CCFM191(最低抑菌浓度=10 mg/L)相比,高耐受镉的植物乳杆菌CCFM8610(最低抑菌浓度>1 000 mg/L)高耐受镉的机制可能与几个方面因素相关:1)植物乳杆菌CCFM8610具有特殊的能量守恒生存模式,在其面对镉暴露时能保持内在均衡的生理状态;温和诱导的细胞防御和修复系统使其在镉暴露时避免剧烈的生理反应而存活下来;2)疏水氨基酸的生物合成增加,提高细胞表面疏水性,阻止镉诱导的蛋白质损伤;3)天然优良的镉结合能力和有效的细胞壁结构,促进其将镉固定在细胞表面,阻止其进入细胞质中;4)对离子通道的严密监管以适应镉诱导的渗透应激;自身有几个在其耐受性中有潜在作用的关键蛋白,包括前噬菌体P2b蛋白18、钙dA、mntA和lp_3327等。本研究中所选用的约氏乳杆菌Cd3-1是从5株耐镉乳酸菌中筛选而得,其最高可耐受1 000 mg镉,对pH为6或7的50 mg/L的镉溶液中的镉吸附率超过或接近30%,表明其具有良好的镉吸附性能。

3.4 耐镉乳酸菌对镉暴露仔鸡组织中钙、铁、锌、锰、铜和硒含量的影响

矿物元素钙、铁、锌、锰、铜和硒是动物生长过程中必需的营养元素,有着重要的生理生化功能。本试验结果表明,镉暴露对这些元素在仔鸡组织中代谢影响程度不同,其中影响较大的是硒。硒是抗氧化剂谷胱甘肽过氧化物酶的活性中心组成成分,而谷胱甘肽过氧化物酶可清除细胞内产生的自由基和过氧化物,从而对细胞起到抗氧化应激的保护作用[34-35]。镉暴露致仔鸡肾脏硒含量显著减少。肾脏是镉毒性作用最主要的靶器官,镉对肾脏的损伤主要是氧化应激,硒含量的减少意味着谷胱甘肽过氧化物酶活性降低,细胞清除镉对肾脏细胞造成的过氧化应激产物的能力下降,表明肾脏中残留的镉已对肾脏细胞造成损伤。补加耐镉乳酸菌使肾脏硒含量有所增加,但仍显著低于对照组,表明补加的耐镉乳酸菌剂量不足以对抗肾脏镉蓄积带来的损害。而与此不同的是,镉暴露使心脏硒含量显著增加。与肾脏相比,心脏中镉含量相对较低,少量的镉刺激心脏细胞的抗氧化应激反应水平提高,使谷胱甘肽过氧化物酶活性增加,因而硒含量也相应增加。此前的相关研究也证实产蛋鸡镉暴露后血液中总抗氧化能力显著增加[18]。补加耐镉乳酸菌使心脏中硒含量进一步增加,增强了心脏的抗氧化功能。

除硒外,仔鸡镉暴露对组织中钙、锌、锰含量均有一定影响,而对铁、铜含量无显著影响。钙、锌、锰与镉同属二价离子,镉借助二价离子通道与钙、锌、锰竞争结合金属硫蛋白而进入组织,同时可取代它们与一些辅酶等结合[36]。李浪等[37]报道,镉可能抑制产蛋鸡钙的肠道吸收,增加粪便和尿中钙的排出,进而致蛋鸡出现钙的负平衡。另有研究表明,镉暴露显著降低产蛋母鸡肾脏中钙含量[18]。本研究中,镉暴露显著降低了仔鸡心脏中钙含量,显著升高了肺脏中钙含量。这些研究结果的差异除与镉的剂量相关外,还可能与机体对钙的生理需求不同有关系。母鸡在产蛋期需要大量的钙,而饲粮提供了充足的钙,保证其在机体内的快速周转利用。仔鸡处于生长期,也需要较多的钙用于骨骼生长,而无产蛋期母鸡钙在骨骼的沉积与动员的交替过程。补加耐镉乳酸菌通过细胞壁和细胞膜吸附部分镉,减少镉与其他二价金属离子竞争结合金属硫蛋白,从而发挥调节二价金属离子的代谢作用。本试验中,补加耐镉乳酸菌后与镉暴露组相比,显著增加了心脏中钙含量,与对照组无显著差异,表明耐镉乳酸菌改善了镉暴露导致的心脏中钙含量的降低。耐镉乳酸菌对镉暴露导致的肺脏中锌和锰的代谢变化的调控效果不同,补加耐镉乳酸菌使肺脏中锰含量与对照组无显著差异,未改善肺脏中锌含量的降低,这可能与镉与锌是同列元素,两者在理化性质上相似性更多相关。

4 结论

① 仔鸡镉暴露时,心脏系数显著降低,肝脏、肾脏、肺脏、脾脏、心脏和胸肌中镉含量显著增加,肾脏中硒含量和心脏中钙含量显著降低。

② 补加耐镉乳酸菌对镉暴露导致的仔鸡心脏系数降低无改善作用,但可降低脾脏中镉含量,亦有降低肝脏中镉含量的趋势,并增加了心脏中硒和钙含量。

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