动物营养学报    2019, Vol. 31 Issue (9): 4251-4261    PDF    
血根碱对脂多糖免疫应激断奶仔猪生长性能、免疫功能及肠道健康的影响
康保聚1,2 , 陈家顺1,2 , 金顺顺2,3 , 田军权2,3 , 王鹏2,3 , 符晨星1 , 伍小松1 , 姚康1,2     
1. 湖南农业大学动物科学技术学院, 长沙 410128;
2. 中国科学院亚热带农业生态研究所, 亚热带农业生态过程重点实验室, 湖南省畜禽健康养殖工程技术中心, 长沙 410025;
3. 中国科学院大学, 北京 100049
摘要: 本试验旨在研究血根碱(SAG)对脂多糖(LPS)免疫应激断奶仔猪生长性能、免疫功能及肠道健康的影响。试验选取(21±1)日龄、平均体重为(6.20±0.09)kg的健康"杜×长×大"断奶仔猪24头,按体重相近原则随机分为4组,分别为对照(CON)组(基础饲粮)、LPS组(基础饲粮+腹腔注射100 μg/kg BW LPS)、SAG组(基础饲粮+50 mg/kg血根碱)和SAG+LPS组(基础饲粮+50 mg/kg血根碱+腹腔注射100 μg/kg BW LPS),每组6个重复,每个重复1头猪。试验采用2×2双因子设计,主因子为血根碱(饲粮中添加、不添加)和LPS(腹腔注射、不注射)。分别于试验第14、21天给断奶仔猪腹腔注射LPS或等量的生理盐水。试验期21 d。结果表明:1)LPS攻毒前(1~14 d),饲粮中添加血根碱显著提高断奶仔猪的平均日采食量(ADFI)和平均日增重(ADG)(P < 0.05),显著降低料重比(F/G)(P < 0.05)。攻毒期间(15~21 d),LPS攻毒显著降低ADG和ADFI(P < 0.05),显著提高F/G(P < 0.05);饲粮中添加血根碱显著提高ADFI和ADG(P < 0.05),显著降低F/G(P < 0.05)。2)攻毒结束后,饲粮中添加血根碱和LPS攻毒均显著提高断奶仔猪的血清免疫球蛋白G(IgG)和免疫球蛋白M(IgM)含量(P < 0.05)。与LPS组相比,SAG+LPS组的血清IgG和IgM含量显著增加(P < 0.05)。3)攻毒结束后,LPS攻毒显著提高断奶仔猪的血清白细胞介素(IL)-1β、IL-6和肿瘤坏死因子-α(TNF-α)含量(P < 0.05),显著降低血清IL-10含量(P < 0.05)。饲粮中添加血根碱显著降低血清IL-1β、IL-6和TNF-α含量(P < 0.05),显著增加血清IL-10含量(P < 0.05)。与LPS组比,SAG+LPS组的血清IL-1β、IL-6和TNF-α含量显著降低(P < 0.05),血清IL-10含量显著增加(P < 0.05)。饲粮中添加血根碱与LPS攻毒的交互作用对血清TNF-α含量有显著影响(P < 0.05)。4)攻毒结束后,LPS攻毒显著提高断奶仔猪的血清D-乳酸(D-LA)含量和二胺氧化酶(DAO)活性(P < 0.05)。饲粮中添加SAG显著降低血清D-LA含量和DAO活性(P < 0.05)。与LPS组比,SAG+LPS组血清D-LA含量和DAO活性显著降低(P < 0.05)。饲粮中添加血根碱与LPS攻毒的交互作用对血清D-LA含量和DAO活性有显著影响(P < 0.05)。5)攻毒结束后,LPS攻毒显著降低断奶仔猪的十二指肠、回肠绒毛高度(VH)及绒毛高度/隐窝深度(V/C),显著提高十二指肠隐窝深度(CD)(P < 0.05)。饲粮中添加血根碱显著提高十二指肠、空肠、回肠VH及V/C,显著降低十二指肠CD(P < 0.05)。与LPS组相比,SAG+LPS组的十二指肠、空肠和回肠VH和V/C显著增加(P < 0.05),十二指肠CD显著降低(P < 0.05)。由此可见,饲粮中添加血根碱可以缓解断奶仔猪免疫应激导致的生长性能下降,提高血清IgG和IgM含量,抑制血清IL-1β、IL-6、TNF-α含量的增加和IL-10含量的降低,进而增强其免疫抵抗能力,缓解肠道通透性增加,并在一定程度上改善小肠黏膜形态结构,从而使断奶仔猪的肠道健康得到改善。
关键词: 血根碱    断奶仔猪    脂多糖    生长性能    免疫功能    肠道健康    
Effects of Sanguinarine on Growth Performance, Immune Function and Gut Heath of Immune-Stressed Weaned Piglets Challenged with Lipopolysaccharide
KANG Baoju1,2 , CHEN Jiashun1,2 , JIN Shunshun2,3 , TIAN Junquan2,3 , WANG Peng2,3 , FU Chenxing1 , WU Xiaosong1 , YAO Kang1,2     
1. College of Animal Science and Technology, Hunan Agricultural University, Changsha 410128, China;
2. Hunan Provincial Engineering Research Center for Healthy Breeding of Livestock and Poultry, Key Laboratory of Agroecological Processes in Subtropical Region, Institute of Subtropical Agriculture, Chinese Academy of Sciences, Changsha 410025, China;
3. University of Chinese Academy of Sciences, Beijing 100049, China
Abstract: This experiment was conducted to investigate the effects of sanguinarine (SAG) on growth performance, immune function and gut heath of immune-stressed weaned piglets challenged with lipopolysaccharide (LPS). Twenty-four healthy "Duroc×Landrace×Yorkshire" weaned piglets at (21±1) days of age with average body weight of (6.20±0.09) kg were randomly assigned to 4 groups with 6 replicates per group and 1 piglet per replicate according to similar body weight. The 4 groups were control (CON) group (basal diet), LPS group (basal diet and injected intraperitoneally with 100 μg/kg BW LPS), SAG group (basal diet supplemented with 50 mg/kg SAG) and SAG+LPS group (basal diet supplemented with 50 mg/kg SAG and injected intraperitoneally with 100 μg/kg BW LPS), respectively. A 2×2 double-factor design was used, and the main factors were SAG (added or not in diet) and LPS (injected intraperitoneally or not). Weaned piglets were injected intraperitoneally with 100 μg/kg BW LPS or an equivalent amount of sterile saline at days 14 and 21. The trail lasted for 21 days. The results showed as follows:1) before challenged with LPS (days 1 to 14), dietary SAG significantly increased average daily feed intake (ADFI) and average daily gain (ADG) of weaned piglets and significantly decreased the ratio of feed to gain (F/G) (P < 0.05). During the period of challenged with LPS (days 15 to 21), LPS challenge significantly decreased ADG and ADFI and significantly increased F/G (P < 0.05), and dietary SAG significantly increased ADFI and ADG and significantly decreased F/G (P < 0.05). 2) After the LPS challenge, both dietary SAG and LPS challenge significantly increased the contents of immunoglobulin G (IgG) and immunoglobulin M (IgM) in serum of weaned piglets (P < 0.05). Compared with LPS group, the contents of IgG and IgM in serum were significantly increased in SAG+LPS group (P < 0.05). 3) After the LPS challenge, LPS challenge significantly increased the contents of interleukin (IL)-1β、IL-6 and tumor necrosis factor-α (TNF-α) in serum of weaned piglets (P < 0.05), and significantly decreased the content of IL-10 in serum (P < 0.05). Dietary SAG significantly decreased the contents of IL-1β、IL-6 and TNF-α in serum (P < 0.05), and significantly increased the content of IL-10 in serum (P < 0.05). Compared with LPS group, the contents of IL-1β、IL-6 and TNF-α in serum were significantly decreased and the content of IL-10 in serum was significantly increased in the SAG+LPS group (P < 0.05). The interaction of dietary SAG and LPS challenge had a significant effect on the content of TNF-α in serum (P < 0.05). 4) After the LPS challenge, LPS challenge significantly increased the content of D-lactate (D-LA) and the activity of diamine oxidase (DAO) in serum of weaned piglets (P < 0.05). Dietary SAG significantly decreased the content of D-LA and the activity of DAO in serum (P < 0.05). Compared with LPS group, the content of D-LA and the activity of DAO in serum were significantly decreased in SAG+LPS group (P < 0.05). The interaction of dietary SAG and LPS challenge had a significant effects on the content of D-LA and the activity of DAO in serum (P < 0.05). 5) After the LPS challenge, LPS challenge significantly decreased villus height (VH) and the ratio of villus height to crypt depth (V/C) of duodenum and ileum of weaned piglets (P < 0.05), and significantly increased crypt depth (CD) of duodenum (P < 0.05). Dietary SAG significantly increased VH and V/C of duodenum, jejunum and ileum (P < 0.05), and significantly decreased CD of duodenum (P < 0.05). Compared with LPS group, VH and V/C were significantly increased of duodenum, jejunum and ileum (P < 0.05), and CD of duodenum was significantly decreased (P < 0.05). In conclusion, dietary SAG can alleviate the decline of growth performance of weaned piglets caused by immunological stress, increase the contents of IgG and IgM in serum, inhabit the increase of IL-1β, IL-6, TNF-α contents and the decrease of IL-10 content in serum, and then improve immune resistance, alleviate the increase of intestinal permeability and improve intestinal mucosal morphology, and improve the intestinal health of weaned piglets.
Key words: sanguinarine    weaned piglets    lipopolysaccharide    growth performance    immune function    gut health    

在现代养猪生产中,由于断奶、疾病、饲养环境条件等原因,仔猪易受细菌、病毒及非病原体[如脂多糖(LPS)]的侵袭,导致采食量下降、饲料转化率降低和死亡率增加等,从而刺激仔猪产生免疫应激,使肠黏膜屏障功能遭到破坏,肠道通透性增加,肠道炎症损伤加剧,最终导致多脏器功能衰竭。现阶段用于缓解免疫应激的方法主要有改善猪舍环境卫生、减少猪与病原体的接触几率[1]、饲粮中添加抗生素[2]和免疫抑制药物[3-4]等。其中抗生素在饲粮中的大量使用不仅会造成细菌耐药性增强,而且会在动物体内残留,直接影响畜产品质量,严重威胁人类健康。免疫抑制药物虽能缓解免疫应激反应,但也会抑制机体的正常免疫功能。研究表明,饲粮中添加红芪多糖、白头翁素、小檗碱等植物提取物能够缓解免疫应激,其可通过抑制炎性细胞因子的产生,强化免疫系统,提高机体抵抗力[5-7]。血根碱(SAG)是一种苯菲啶异喹啉生物碱[8],其在抗炎[9-10]、抑菌[11-13]、提高机体免疫力[14-15]、改善肠道健康和功能维持[16-17]等方面能发挥着重要作用,且具有易降解、低残留、无环境公害等特点。研究表明,饲粮中添加0.50 mg/kg血根碱可提高断奶仔猪的平均日采食量(ADFI)及血清总蛋白(TP)、免疫球蛋白M(IgM)和免疫球蛋白G(IgG)含量,降低料重比(F/G)和腹泻率[14]。Liu等[18]研究发现,饲粮中添加40 mg/kg血根碱能提高断奶仔猪的ADFI和平均日增重(ADG)。陈家顺等[19]研究发现,饲粮中添加血根碱可通过改善肠道黏膜发育情况,增进肠黏膜免疫功能,进而促进早期断奶仔猪更加健康快速地生长。Bavarsadi等[20]、姬晓琪等[21]和Khadem等[22]研究显示,饲粮中添加血根碱可增强鸡的细胞和体液免疫,降低炎症因子水平,改善肠道结构和健康状况。由此可见,血根碱是一种潜在的可用于缓解畜禽免疫应激的天然植物添加剂。鉴于此,本试验以腹腔注射LPS构建仔猪免疫应激模型,并在饲粮中添加血根碱,探讨其对LPS免疫应激断奶仔猪生长性能、免疫功能及肠道健康的影响,以期为缓解免疫应激提供一种新的选择方向和理论基础,并为血根碱在养猪生产中的应用提供一定的参考。

1 材料与方法 1.1 试验材料

血根碱制剂(血根碱含量为1.5%)由湖南美可达生物资源有限公司提供,LPS型号为大肠杆菌(E. coli) serotype 055 : B5,由美国Sigma Chemical公司提供,将其以无菌生理盐水配成浓度为100 μg/mL的稀释液,超滤除菌。

1.2 试验动物与试验设计

试验选取(21±1)日龄、平均体重为(6.20±0.09) kg的健康“杜×长×大”断奶仔猪24头,按体重相近原则随机分为4组,分别为对照(CON)组(基础饲粮)、LPS组(基础饲粮+腹腔注射100 μg/kg BW LPS)、SAG组(基础饲粮+50 mg/kg血根碱)和SAG+LPS组(基础饲粮+50 mg/kg血根碱+腹腔注射100 μg/kg BW LPS),每组6个重复,每个重复1头猪。试验期21 d。试验采用2×2双因子设计,主因子为血根碱(饲粮中添加、不添加)和LPS(腹腔注射、不注射)。分别于试验第14、21天给仔猪腹腔注射LPS或等量的生理盐水,于最后一次注射LPS 12 h后麻醉致死取样。

1.3 试验饲粮

基础饲粮的配制参照NRC(2012)仔猪营养需要标准,其组成及营养水平见表 1

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)
1.4 饲养管理

本试验于中国科学院亚热带农业生态研究所动物饲养实验室进行,仔猪采用单笼饲养,全封闭管理,栏舍为不锈钢材质,乳头式自由饮水器,并不定期对猪舍进行消毒、卫生清洁。仔猪每天喂食4次,粉料饲喂,时间分别为07:30、11:30、18:30和21:30,自由饮水和采食,以食槽略有剩料为原则。

1.5 样品采集

于试验第21天,仔猪腹腔注射LPS 3 h后前腔静脉采血10 mL,静置15 min,4 ℃下3 000 r/min离心15 min分离制备血清,-80 ℃保存待用。腹腔注射LPS 12 h后将仔猪麻醉处死,取十二指肠、空肠、回肠肠断各约2 cm,于10%中性福尔马林溶液中固定,以备小肠形态学检测。

1.6 测定指标及方法 1.6.1 生长性能

于试验第1、14和21天对仔猪逐个进行空腹称重,并准确记录;每天准确称量每头仔猪的给料量和剩料量,并记录每天的采食量。分别计算每组仔猪LPS攻毒前、后的ADFI、ADG和F/G。计算公式为:

1.6.2 血清生化指标

采用全自动生化仪检测血清IgG、IgM含量,测定试验在中国科学院亚热带农业生态研究所生态楼实验室进行;采用酶联免疫吸附试验(ELISA)试剂盒检测血清肿瘤坏死因子-α(TNF-α)、白细胞介素(IL)-8、IL-6、IL-1β和IL-10含量,试剂盒由武汉华美生物工程有限公司提供。

1.6.3 肠道通透性

采用试剂盒测定血清二胺氧化酶(DAO)活性和D-乳酸(D-LA)含量,试剂盒由南京建成生物工程研究所提供,操作方法严格按照说明书进行。

1.6.4 肠道形态结构

将10%固定液中的十二指肠、空肠、回肠肠道组织取出,经常规水洗、浸蜡、包埋、切片、苏木精-伊红(HE)染色后,在光学显微镜下观察,选取6个走向延伸良好的视野,用Magic Images Advanced 3.2软件测量绒毛高度(VH)和隐窝深度(CD),并计算绒毛高度/隐窝深度(V/C)。

1.7 数据分析

所有试验数据均用Excel 2016件初步处理,采用SAS 9.2软件进行2×2双因素统计分析,该统计模型包括血根碱(饲粮中添加、不添加)、LPS(腹腔注射、不注射)及其交互作用。部分数据采用Duncan氏法进行单因素方差分析(one-way ANOVA),P < 0.05表示差异显著。所有数据均以“平均值±标准误”表示。

2 结果与分析 2.1 血根碱对LPS免疫应激断奶仔猪生长性能的影响

表 2可知,LPS攻毒前(1~14 d),饲粮中添加血根碱显著提高断奶仔猪的ADFI和ADG(P < 0.05),显著降低F/G(P < 0.05),对体重无显著影响(P>0.05)。攻毒期间(15~21 d),LPS攻毒显著降低断奶仔猪的ADG和ADFI(P < 0.05),显著提高F/G(P < 0.05),对体重无显著影响(P>0.05);饲粮中添加血根碱显著提高ADFI和ADG(P < 0.05),显著降低F/G(P < 0.05)。饲粮中添加血根碱与LPS攻毒的交互作用对断奶仔猪的体重、ADFI、ADG和F/G均无显著影响(P>0.05)。由此推断,LPS攻毒可以诱发断奶仔猪严重的免疫应激反应,使其生长性能下降;饲粮中添加血根碱不仅可以提高生长性能,还能缓解LPS免疫应激引起的生长性能下降。

表 2 血根碱对LPS免疫应激断奶仔猪生长性能的影响 Table 2 Effects of SAG on growth performance of immune-stressed weaned piglets challenged with LPS (n=6)
2.2 血根碱对LPS免疫应激断奶仔猪血清免疫球蛋白含量的影响

表 3可知,攻毒结束后,饲粮中添加血根碱和LPS攻毒均可显著提高断奶仔猪的血清IgG和IgM含量(P < 0.05);与LPS组相比,SAG+LPS组的血清IgG和IgM含量显著增加(P < 0.05)。饲粮中添加血根碱与LPS攻毒的交互作用对断奶仔猪的血清IgG和IgM含量无显著影响(P>0.05)。由此推断,LPS免疫应激激活了断奶仔猪的免疫系统来进行防御和自我保护,饲粮中添加血根碱使这种防护作用进一步加强。

表 3 血根碱对LPS免疫应激断奶仔猪血清免疫球蛋白含量的影响 Table 3 Effects of SAG on the contents of immunoglobulin in serum of immune-stressed weaned piglets challenged with LPS
2.3 血根碱对LPS免疫应激断奶仔猪血清炎症因子含量的影响

表 4可知,攻毒结束后,LPS攻毒显著提高断奶仔猪的血清IL-1β、IL-6和TNF-α含量(P < 0.05),显著降低血清IL-10含量(P < 0.05);饲粮中添加血根碱显著降低血清IL-1β、IL-6和TNF-α含量(P < 0.05),显著增加血清IL-10含量(P < 0.05);与LPS组比,SAG+LPS组的血清IL-1β、IL-6和TNF-α含量显著降低(P < 0.05),血清IL-10含量显著增加(P < 0.05)。各组断奶仔猪的血清IL-8含量无显著差异(P>0.05)。饲粮中添加血根碱与LPS攻毒的交互作用对断奶仔猪的血清TNF-α含量有显著影响(P < 0.05)。由此推断,LPS免疫应激可以诱发断奶仔猪的炎症反应,而饲粮中添加血根碱可以缓解炎症反应。

表 4 血根碱对LPS免疫应激断奶仔猪血清炎症因子含量的影响 Table 4 Effects of SAG on the contents of inflammatory factor in serum of immune-stressed weaned piglets challenged with LPS
2.4 血根碱对LPS免疫应激断奶仔猪肠道通透性的影响

表 5可知,攻毒结束后,LPS攻毒显著提高断奶仔猪的血清D-LA含量和DAO活性(P < 0.05);饲粮中添加SAG显著降低血清D-LA含量和DAO活性(P < 0.05);与LPS组比,SAG+LPS组的血清D-LA含量和DAO活性显著降低(P < 0.05)。饲粮中添加血根碱与LPS攻毒的交互作用对断奶仔猪的血清D-LA含量和DAO活性有显著影响(P < 0.05)。由此推断,LPS免疫应激可引起断奶仔猪的肠道损伤,使肠道通透性增加,饲粮中添加血根碱可缓解这种肠道损伤和通透性改变。

表 5 血根碱对LPS免疫应激断奶仔猪肠道通透性的影响 Table 5 Effects of SAG on intestinal permeability of immune-stressed weaned piglets challenged with LPS
2.5 血根碱对LPS免疫应激断奶仔猪肠道形态结构的影响

表 6图 1可知,攻毒结束后,LPS攻毒显著降低断奶仔猪的十二指肠、回肠VH及V/C,显著提高十二指肠CD(P < 0.05),对空肠VH、CD、V/C和回肠CD无显著影响(P>0.05);饲粮中添加血根碱显著提高十二指肠、空肠、回肠VH及V/C,显著降低十二指肠CD(P < 0.05),对空肠、回肠CD无显著影响(P>0.05);与LPS组相比,SAG+LPS组的十二指肠、空肠和回肠VH和V/C显著增加(P < 0.05),十二指肠CD显著降低(P < 0.05),空肠、回肠CD无显著变化(P>0.05)。饲粮中添加血根碱与LPS攻毒的交互作用对断奶仔猪的十二指肠、空肠和回肠的VH、CD及V/C无显著影响(P>0.05)。由此推断,LPS免疫应激对断奶仔猪的小肠黏膜造成损伤,使其比表面积减小,而饲粮中添加血根碱会在一定程度上缓解这种损伤,有益于断奶仔猪小肠健康及发育。

表 6 血根碱对LPS免疫应激断奶仔猪肠道形态结构的影响 Table 6 Effects of SAG on intestinal morphology of immune-stressed weaned piglets challenged with LPS
图 1 断奶仔猪肠道形态结构 Fig. 1 Intestinal morphology of weaned piglets (100×)
3 讨论 3.1 血根碱对LPS免疫应激断奶仔猪生长性能的影响

免疫应激是动物在受到外界抗原侵袭时,机体为抵御其危害,免疫系统被高度激活,进而引发动物代谢和行为的改变,导致生长性能下降、饲料利用率降低、生长迟滞的一种现象[23]。目前腹腔注射一定剂量的LPS是模拟免疫应激最典型的方式之一。LPS是革兰氏阴性菌的重要组分多糖,注射入体内,动物会产生发热、呕吐、腹泻和厌食等多种症状。本试验结果显示,注射LPS后,断奶仔猪出现强烈的高烧、呕吐、腹泻、嗜睡、24 h内几乎不采食、精神状态极差等症状,说明本次试验用LPS营造免疫应激模型是成功的。然而,腹腔注射LPS模拟免疫应激虽为科研工作者普遍采用,但现实猪场中存在的是较温和的持续慢性免疫应激,而LPS刺激产生的是急性免疫应激,反应较剧烈,发挥效价有一定的时间限度,且与LPS的注射剂量、动物的年龄等密切相关,故而在仔猪上科研工作者多采用低剂量多次注射的方法来模拟免疫应激[24-25]。又考虑到短期连续多次注射LPS会使仔猪产生耐受性,还可能出现死亡[26],而且注射过程产生的应激可能会严重影响甚至掩盖LPS导致的应激效果,因此本试验采用第14天和第21天分别注射1次LPS的方法来模拟猪场免疫应激,Zhu等[27]和Yi等[28]报道的LPS注射试验设计与本试验类似。已有报道证实,LPS应激可造成仔猪生长性能显著降低[29-30]。本试验结果显示,注射LPS显著降低断奶仔猪的ADG和ADFI,同时显著提高F/G,与上述报道基本一致。血根碱是一种天然的植物提取物,其作为一种饲料添加剂在动物营养和饲料中的应用,主要是作为抗生素的替代物来发挥促生长作用。Kantas等[31]研究表明,饲粮中添加血根碱可显著提高断奶仔猪的体重、ADG、ADFI和饲料转化率。Chen等[32]研究证实,饲粮中添加血根碱可以显著提高仔猪的ADG和ADFI,对仔猪的F/G有降低的趋势。李美荃等[33]和蔡鹏等[34]研究也证明,饲粮中添加不同水平血根碱可显著提高仔猪的ADG和ADFI,并显著降低F/G。本试验研究发现,LPS攻毒前(1~14 d),饲粮中添加50 mg/kg的血根碱制剂显著提高断奶仔猪的ADG和ADFI,显著降低F/G,这与上述结果基本一致。LPS攻毒期间(15~21 d),饲粮中添加血根碱显著提高断奶仔猪的ADFI和ADG,显著降低F/G,这表示血根碱有益于仔猪抵御LPS诱发的应激反应,调控其导致的生长抑制作用。原因可能是血根碱能够抑制一些炎症因子的过多分泌[10, 35],促进对色氨酸、苯丙氨酸等氨基酸的利用,改善机体健康状况,进而促进生长发育[36]

3.2 血根碱对LPS免疫应激断奶仔猪免疫功能的影响

免疫球蛋白IgM和IgG由B细胞分泌产生,是机体体液免疫的重要组成部分,也是机体免疫功能的重要衡量指标。本试验结果显示,注射LPS使断奶仔猪的血清IgM和IgG含量显著升高,而饲粮中添加血根碱使血清IgM和IgG含量更高,原因可能是仔猪受LPS刺激诱发了免疫应激反应,被激活的免疫系统启动免疫应答,由浆细胞迅速分泌大量的IgM和IgG进行防御,但免球蛋白的合成需要大量的能量,而血根碱既能促进小肠的发育[19-22],使其对营养物质的消化吸收能力更强,同时还能保护细胞线粒体免受LPS诱导氧化应激造成的损伤[37],进而为机体提供更多的能量,最终使浆细胞分泌更多的IgM和IgG抗体。

LPS诱导免疫应激,体内T细胞、巨噬细胞、单核细胞等受到刺激释放细胞因子[9, 38]。IL-1β能引起急性和慢性炎症的发生[39];IL-6通过强化其他炎性细胞因子的作用来参与炎症反应的发展[38];IL-8主要由单核-巨噬细胞产生,能诱导超氧化物的形成,造成细胞和组织损伤[40];TNF-α是一种能发挥多种不同生理作用的促炎细胞因子,能够诱导肠上皮细胞凋亡[41-42];IL-10是一种抑炎因子,能够通过阻止核转录因子-κB(NF-κB)的活化来抑制其他炎性因子的产生,是免疫反应重要的调节因子[43]。本试验结果显示,攻毒结束后,LPS刺激使断奶仔猪的血清IL-1β、IL-6和TNF-α含量显著升高,血清IL-10含量显著降低;饲粮中添加血根碱使血清IL-1β、IL-6和TNF-α含量显著降低,血清IL-10含量显著升高。这表明饲粮中添加血根碱能抑制仔猪免疫应激诱导的炎症反应,促进机体健康,原因可能是血根碱能通过抑制核因子κB抑制因子(IκB)的磷酸化,阻碍NF-κB激活,减少炎性细胞因子的表达,最终起到抑制炎症反应的作用[9]

3.3 血根碱对LPS免疫应激断奶仔猪肠道健康的影响

小肠是动物机体内营养物质消化和吸收的主要场所,因此小肠黏膜形态结构和通透性可以反映出动物的健康状况和对营养物质消化吸收能力的强弱。小肠绒毛越高,隐窝越浅,二者比值越大,说明吸收面积越大,功能越好。Sukhotnik等[44]和王蕾等[45]研究证实,LPS刺激可对小肠黏膜造成损伤,致使绒毛萎缩,隐窝加深。本试验结果显示,攻毒结束后,LPS刺激使断奶仔猪的十二指肠、回肠VH及V/C显著降低,十二指肠CD显著增加,与上述报道相一致。本试验还发现,LPS攻毒后,饲粮中添加血根碱使断奶仔猪的十二指肠、空肠、回肠的VH及V/C显著增加,十二指肠CD显著降低。陈家顺等[19]研究表明,饲粮中添加50 mg/kg的血根碱能显著提高仔猪小肠VH和V/C,有降低空肠CD的趋势,与本试验结果相一致。这说明血根碱可以缓解仔猪免疫应激诱导的小肠形态结构损伤,可能原因如下:1)血根碱能增强食欲,提高采食量,保持了更多的能量供给;2)血根碱能保护细胞线粒体免受LPS诱导氧化应激造成的损伤,改善其能量状态,减少小肠上皮细胞凋亡[37, 46]

D-LA在哺乳动物体内由肠道微生物代谢产生,但哺乳动物缺乏迅速代谢D-LA的酶,当肠黏膜受损、通透性增加时,D-LA会进入血液,导致血清D-LA含量增加,因此,血清D-LA含量高低可以反映肠道的健康状态[47]。DAO是哺乳动物肠上皮细胞内酶,参与蛋白质、核酸质等的合成[48]。只有肠黏膜损伤时,DAO才会进入血液,因此血清DAO活性也可反映肠道的健康状态。已有报道证实,LPS刺激会导致仔猪肠黏膜紧密连接蛋白表达量下降,通透性增加[44]。本试验结果显示,攻毒结束后,LPS刺激显著提高断奶仔猪的血清D-LA含量和DAO活性,这与以上结果相符。此外,本试验结果还显示,LPS刺激下,饲粮中添加血根碱使断奶仔猪的血清D-LA含量和DAO活性显著降低,这表明LPS刺激造成了小肠黏膜损伤,而血根碱能缓解这种损伤。原因可能是血根碱能促进小肠黏膜紧密连接蛋白的表达,抑制炎性细胞因子的表达,从而降低对肠道黏膜屏障的损伤[49-50]

4 小结

饲粮中添加血根碱可以缓解断奶仔猪免疫应激导致的生长性能下降,提高血清IgG和IgM含量,抑制血清IL-1β、IL-6、TNF-α含量的增加和IL-10含量的降低,进而增强其免疫抵抗能力,缓解肠道通透性增加,并在一定程度上改善小肠黏膜形态结构,从而使断奶仔猪的肠道健康得到改善。因此,血根碱可有效缓解免疫应激,用于减少或替代抗生素在断奶仔猪饲粮中使用。

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