Effects of Broussonetia papyrifera Leaf Polysaccharide Supplementation in Formula Milk on Growth Performance and Ileal Barrier Function in Piglets Challenged by Rotavirus

TAN Dayan; FAN Xiangqi; MAO Xiangbing; HUANG Bing; YANG Heng; ZHANG Feiran; WANG Quyuan; WANG Huifen; PU Junning

doi:10.12418/CJAN2026.396

2026 , Vol. 38 >Issue 7: 4946 - 4954

DOI: https://doi.org/10.12418/CJAN2026.396

RESEARCH PAPER

Effects of Broussonetia papyrifera Leaf Polysaccharide Supplementation in Formula Milk on Growth Performance and Ileal Barrier Function in Piglets Challenged by Rotavirus

TAN Dayan ,
FAN Xiangqi ^* ,
MAO Xiangbing ^,^** ,
HUANG Bing ,
YANG Heng ,
ZHANG Feiran ,
WANG Quyuan ,
WANG Huifen ,
PU Junning

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Key Laboratory of Animal Disease-Resistant Nutrition of Sichuan Province, Institute of Animal Nutrition, Sichuan Agricultural University, Chengdu 611130, China

^** professor, E-mail: acatmxb2003@163.com

^* Contributed equally

Received date: 2025-12-19

Online published: 2026-07-14

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Abstract

This experiment was conducted to explore the effects of Broussonetia papyrifera leaf polysaccharide (BPP) supplementation in formula milk on growth performance and ileal barrier function in piglets challenged by rotavirus. Twenty-four 7-day-old healthy Duroc×Landrace×Yorkshire piglets were selected and randomly divided into 2 groups with 12 piglets in each group using a 2×2 factor design. They were fed formula milk supplemented with 0 and 110 mg/kg BPP, respectively. The experiment lasted for 24 days. On day 21, six piglets were randomly selected from each of the two groups for RV challenge, while the remaining piglets were not challenged. The results showed as follows: 1) RV challenge significantly decreased the average daily gain (ADG) of piglets (P<0.05), and induced moderate-to-severe diarrhea in piglets (incidence was 83.33%); BPP supplementation in formula milk significantly alleviated the decline of ADG caused by RV challenge (P<0.05), and significantly decreased the incidence of moderate-to-severe diarrhea (P<0.05). 2) RV challenge significantly decreased the villus height and the villus height to crypt depth ratio in ileum (P<0.05), significantly increased the crypt depth in ileum (P<0.05), simultaneously significantly increased the contents of RV-specific immunoglobulin M (RV-IgM), protein carbonyl, and malondialdehyde (MDA) in ileal mucosa (P<0.05), and significantly decreased the total antioxidant capacity (T-AOC) in ileal mucosa (P<0.05); BPP supplementation in formula milk significantly alleviated the negative effects of RV challenge on ileal morphology and antioxidant indices in ileal mucosa (P<0.05). 3) RV challenge significantly increased the mRNA relative expression levels of Caspase-3 and B-cell lymphoma-2 associated X protein (Bax) in ileal mucosa and the ratio of Bax to B-cell lymphoma-2 (Bcl-2) (P<0.05); BPP supplementation in formula milk significantly increased the mRNA relative expression levels of mucin 1 (MUC1), Occludin and Bcl-2 in ileal mucosa (P<0.05), significantly decreased the Bax mRNA relative expression level and the ratio of Bax to Bcl-2 in ileal mucosa (P<0.05), and significantly alleviated the negative effects of RV challenge on the mucosal barrier function and apoptosis in ileum (P<0.05). In conclusion, BPP supplementation in formula milk can effectively alleviate the decline in growth performance and the incidence of diarrhea in piglets induced by RV infection by enhancing the antioxidant capacity of ileal mucosa, inhibiting excessive apoptosis, and improving intestinal morphology and barrier function.

Key words： Broussonetia papyrifera leaf polysaccharide; piglets; rotavirus; ileal barrier function; antioxidant capacity

Cite this article

TAN Dayan , FAN Xiangqi , MAO Xiangbing , HUANG Bing , YANG Heng , ZHANG Feiran , WANG Quyuan , WANG Huifen , PU Junning . Effects of Broussonetia papyrifera Leaf Polysaccharide Supplementation in Formula Milk on Growth Performance and Ileal Barrier Function in Piglets Challenged by Rotavirus[J]. Chinese Journal of Animal Nutrition, 2026 , 38(7) : 4946 -4954 . DOI: 10.12418/CJAN2026.396

轮状病毒(rotavirus,RV)属于双链RNA病毒科,被广泛认为是诱发全球幼龄动物及婴幼儿急性病毒性胃肠炎和严重脱水性腹泻的主要病原体之一^[1-2]。流行病学监测数据显示,仔猪群体(特别是新生期和幼龄期)对RV呈现高度易感性,患病后典型临床症状包括剧烈腹泻、呕吐以及生长发育受阻,严重时可导致死亡,这给生猪养殖产业造成了不可忽视的经济损失^[3-4]。RV主要侵袭小肠(包括十二指肠、空肠和回肠)的成熟绒毛上皮细胞,导致绒毛萎缩、脱落,破坏肠道黏膜屏障,进而引发吸收不良性腹泻和继发性感染^[1-2,4]。回肠虽在小肠的末段,但依然在肠道屏障功能中发挥了重要作用^[5]。因此,保护回肠黏膜屏障功能的完整性对于缓解RV感染引发的腹泻至关重要。

构树(Broussonetia papyrifera)作为一种药食同源的木本植物,在我国资源丰富、分布广泛,整株具有药用价值,其叶片富含蛋白质、氨基酸、黄酮类及多糖等多种营养和活性成分^[6-7]。构树叶多糖(Broussonetia papyrifera leaf polysaccharide,BPP)是从构树叶中提取的天然大分子活性物质。现代药理学研究表明,植物多糖具有广谱的生物活性,特别是其抗氧化及肠道黏膜修复功能日益受到关注^[8-10]。本团队前期研究表明,灌服BPP可缓解氧化鱼油饲粮诱导的大鼠肠道损伤,从而改善肠道屏障的完整性^[9]。但关于BPP作为营养方案在缓解幼龄动物病毒(如RV)感染方面的研究尚处于起步阶段。

基于此,本试验在建立仔猪RV感染模型的基础上,通过探究在配方乳中添加BPP对RV攻毒仔猪腹泻表型和回肠黏膜屏障功能的影响,并通过细胞凋亡和抗氧化功能的分析初步探究其可能机制,旨在进一步阐明BPP的抗逆性,为其作为新型功能性饲料添加剂在预防幼龄动物(尤其是仔猪)病毒性腹泻中的开发和应用提供依据。

1 材料与方法

1.1 试验材料

试验所用的BPP由本研究团队采用水提醇沉法制备,新鲜构树叶采摘自四川农业大学成都校区,具体制备过程参考余伟^[11]的方法,纯度>80%,其结构信息参见本团队前期研究^[9]。RV为OSU毒株G5P9株(ATCC#VR-893),为本团队保存沿用,采用猪小肠上皮细胞系IPEC-J2进行培养、强化和滴度测定^[12]。

1.2 试验动物和设计

本研究的动物试验方案经过四川农业大学实验动物伦理与福利委员会审核批准(批准编号:SICAU-2022-0136)。

试验从6头健康的母猪所带仔猪中选出24头(每窝4头)7日龄健康“杜×长×大(DLY)”阉公猪[初始体重为(2.46±0.06) kg],采用2×2因子设计,主效应为配方乳中BPP的添加水平(0或110 mg/kg)以及是否进行RV攻毒(灌喂病毒液或等量同源培养液)。试验期24 d。试验第1天,基于体重相近原则将所有仔猪随机分配至2组(每组12头),分别提供添加或不含BPP的配方乳。试验第21天,先对所有仔猪经口灌注5 mL无菌100 mmol/L碳酸氢钠(NaHCO₃)溶液以中和胃酸;间隔15 min后,从2组中各随机抽取6头仔猪进行RV攻毒(灌服25 mL滴度为1.6×10⁷ TCID₅₀/mL的RV病毒液,TCID₅₀为半数组织培养感染剂量),其余仔猪(未攻毒)则灌服等体积无菌的同源培养液。

1.3 试验饲粮

基础配方乳参考Han等^[13]进行配制,配方乳与温开水按1∶4(体积比)比例制成液态;试验配方乳是在基础配方乳中添加110 mg/kg BPP,且BPP是以等量替代基础配方乳中全脂奶粉进行添加。基础配方乳组成及营养水平见表1。

表1 基础配方乳组成及营养水平(风干基础)

Table 1 Composition and nutrient levels of the basal formula milk (air-dry basis) %

项目Items		含量Content
原料Ingredients
全脂奶粉Whole milk powder		58.00
乳清浓缩蛋白Whey protein concentrate		25.00
酪蛋白Casein		5.70
椰子油Coconut oil		10.00
磷酸氢钙CaHPO₄		0.10
氯化胆碱Choline chloride		0.10
维生素预混料Vitamin premix¹⁾		0.10
矿物质预混料Mineral premix²⁾		0.50
L-精氨酸L-arginine		0.06
DL-蛋氨酸DL-methionine		0.06
L-赖氨酸盐酸盐L-lysine·HCl		0.30
L-苏氨酸L-threonine		0.03
L-色氨酸L-tryptophan		0.05
合计Total		100.00
营养水平Nutrient levels³⁾
粗蛋白质Crude protein		24.87
消化能Digestible energy/(MJ/kg)		18.45
钙Calcium		0.86
总磷Total phosphorus		0.77
赖氨酸Lysine		2.14
蛋氨酸Methionine		0.65
苏氨酸Threonine		1.33
精氨酸Arginine		0.84

1)维生素预混料为每千克配方乳提供 The vitamin premix supplied the following per kg of the formula milk:VA 3 313 IU,VE 22 IU,VD₃ 400 IU,VB₁ 1.5 mg,VB₂ 5 mg,VB₆ 2 mg,VB₁₂ 40 μg,VK₃ 1 mg,叶酸 folic acid 1.50 mg,烟酸 nicotinic acid 20 mg,泛酸 pantothenic acid 15 mg,生物素 biotin 0.1 mg。

3)消化能根据《中国饲料成分及营养价值表(2024年第35版)》中原料的能值计算得到,粗蛋白质、钙、总磷和氨基酸为实测值。Digestible energy was calculated on basis of the energy values of raw materials in Tables of Feed Composition and Nutritive Values in China (35th edition, 2024), while crude protein, calcium, total phosphorus and amino acids were measured values.

2)矿物质预混料为每千克配方乳提供 The mineral premix supplied the following per kg of the formula milk:Zn 90 mg,Mn 4.0 mg,Fe 90 mg,Cu 6.0 mg,Se 0.3 mg,I 0.2 mg。

1.4 饲养管理

动物试验于四川农业大学动物营养研究所教学试验基地环境控制室进行。所有仔猪使用新生仔猪代谢笼饲喂,温度28~31 ℃,相对湿度60%~70%。整个饲养阶段配方乳用温开水现配现用,每次饲喂完成后立即清洗器具并消毒,每天饲喂7次(06:00、09:00、12:00、15:00、18:00、21:00和24:00各1次),每次至仔猪停止采食,所有仔猪自由饮水。试验过程中密切观察猪只状态,定期对栏舍进行冲洗清洁,确保饲养环境干燥、通风且卫生达标。分别于试验第21天和第25天,对所有仔猪进行空腹称重,计算攻毒后平均日增重(ADG);试验第21~24天,每日进行结料,计算平均日采食量(ADFI)。

1.5 测定指标及方法

1.5.1 饲粮营养成分含量

饲粮粗蛋白质、钙、总磷和氨基酸含量分别参照GB/T 6432—2018、GB/T 6436—2018、GB/T 6437—2018和GB/T 18246—2019中方法进行测定。

1.5.2 样品采集

于试验第25天对仔猪进行空腹称重,随后按50 mg/kg BW剂量心脏注射戊巴比妥钠,并经颈静脉放血实施屠宰。截取回肠中段约2 cm,用生理盐水轻轻冲洗内容物后,立即置于4%多聚甲醛溶液中固定,用于形态学观察;剩余回肠用冰冷生理盐水漂洗后,用载玻片小心收集回肠黏膜,样品置于液氮中速冻并于-80 ℃储存备用。

1.5.3 腹泻情况

RV攻毒后,每天3次对每头仔猪腹泻情况进行评分。具体评分和标准为:0分(正常硬便,条状或粒状);1分(软便,形状保持良好);2分(糊状便,无固定形状);3分(水样便,液状或水粪分离)。当评分≥2时定义为中重度腹泻,计算中重度腹泻发生率(100×中重度腹泻发生次数/评分次数)^[14]。

1.5.4 回肠组织形态学观察

回肠组织形态学观察方法参考Mao等^[12]。

1.5.5 回肠黏膜RV特异性免疫球蛋白M(RV-specific immunoglobulin M,RV-IgM)含量和抗氧化指标

回肠黏膜组织样品预处理方法参考Mao等^[12]。RV-IgM含量采用上海诺渊实业有限公司的酶联免疫吸附测定(ELISA)试剂盒测定。总抗氧化能力(total antioxidant capacity,T-AOC)、过氧化氢酶(catalase,CAT)和超氧化物歧化酶(superoxide dismutase,SOD)活性及蛋白质羰基和丙二醛(malondialdehyde,MDA)含量采用南京建成生物工程研究所的试剂盒测定;谷胱甘肽过氧化物酶(glutathione peroxidase,GSH-Px)活性采用上海碧云天生物技术股份有限公司的试剂盒测定;8-羟基脱氧鸟苷(8-hydroxydeoxyguanosine,8-OHdG)含量采用成都安普迪生物科技有限公司的ELISA试剂盒测定。

1.5.6 回肠黏膜紧密连接蛋白、黏蛋白和细胞凋亡相关基因表达

回肠黏膜黏蛋白1(MUC1)、闭合蛋白(Occludin)、半胱氨酸天冬氨酸蛋白酶-3(Caspase-3)、B细胞淋巴瘤-2相关X蛋白(Bax)和B细胞淋巴瘤-2(Bcl-2)mRNA相对表达量采用实时荧光定量PCR(RT-qPCR)法测定,详细操作流程参考Wang等^[15]。

1.6 数据统计分析

试验数据采用Excel 2021进行初步整理,并采用SPSS 20.0软件进行统计分析。仔猪中重度腹泻发生率数据采用卡方检验,并对攻毒条件下未添加或添加BPP配方乳饲喂的2个组进行独立样本t检验;其余指标均采用双因素方差分析(two-way ANOVA)进行处理,统计模型涵盖RV攻毒和添加BPP配方乳2个主效应,并考量二者的交互效应。若分析结果显示差异显著,则进一步运用Duncan氏法进行多重比较分析。统计学显著性水平设定为P<0.05,0.05≤P<0.10被判定为具有差异显著趋势。结果数据以“平均值±标准误”形式呈现。

2 结果

2.1 配方乳中添加BPP对RV攻毒仔猪生长性能和中重度腹泻发生率的影响

由表2可知,RV攻毒显著降低了仔猪ADG(P<0.05),有降低第25天体重(P=0.080)和ADFI(P=0.079)的趋势,并诱导仔猪发生中重度腹泻(发生率83.33%)。配方乳中添加BPP显著提高了仔猪第25天体重和ADG(P<0.05);且在RV攻毒仔猪中,配方乳中添加BPP显著缓解了RV攻毒导致的ADG降低(P<0.05),显著降低了RV攻毒诱导的中重度腹泻发生率(P<0.05),仅为58.33%。

表2 配方乳中添加BPP对RV攻毒仔猪生长性能和中重度腹泻发生率的影响

Table 2 Effects of BPP supplementation in formula milk on growth performance and incidence of moderate-to-severe diarrhea in piglets challenged by RV

项目 Items	未添加BPP Without BPP supplementation		添加BPP BPP supplementation		P值 P-value
项目 Items	对照组 Control group	RV攻毒组 RV challenged group	BPP组 BPP group	RV攻毒组 RV challenged group	轮状病毒 RV	构树叶多糖 BPP	轮状病毒× 构树叶多糖 RV×BPP
第21天体重 Body weight on day 21/kg	7.74±0.39	7.49±0.42	8.69±0.34	8.55±0.30	0.600	0.012	0.883
第25天体重 Body weight on day 25/kg	8.47±0.43^ab	7.41±0.58^b	9.75±0.46^a	9.17±0.26^a	0.080	0.003	0.599
平均日采食量 ADFI/(g/d)	336.25±25.46	287.00±36.52	366.25±32.23	293.89±35.68	0.079	0.582	0.726
平均日增重 ADG/(g/d)	242.78±35.74^ab	-25.67±56.79^c	354.44±44.80^a	207.22±43.74^b	<0.001	0.001	0.197
中重度腹泻发生率 Incidence of moderate- to-severe diarrhea/%	0.00±0.00	83.33±3.33	0.00±0.00	58.33±9.80^*

	同行数据肩标不同字母表示差异显著(P<0.05),下表同。*表示2个RV攻毒组间差异显著(P=0.036)。
	In the same row, values with different letter superscripts mean significant difference (P<0.05), the same as below. * indicated significant difference between the two RV challenged groups (P=0.036).

2.2 配方乳中添加BPP对RV攻毒仔猪回肠形态及黏膜RV-IgM含量和抗氧化指标的影响

由表3可知,RV攻毒显著降低了仔猪回肠绒毛高度和绒隐比(P<0.05),显著提高了回肠隐窝深度(P<0.05),同时显著提高了回肠黏膜RV-IgM、蛋白质羰基和MDA含量(P<0.05),并显著降低了回肠黏膜T-AOC(P<0.05)。配方乳中添加BPP显著提高了仔猪回肠绒毛高度、绒隐比,回肠黏膜T-AOC、CAT和GSH-Px活性(P<0.05),有提高回肠黏膜SOD活性的趋势(P=0.082),显著降低了回肠隐窝深度及回肠黏膜蛋白质羰基、MDA和8-OHdG含量(P<0.05);且在RV攻毒仔猪中,配方乳中添加BPP显著缓解了RV攻毒对回肠绒毛高度、隐窝深度和绒隐比,回肠黏膜T-AOC、CAT活性及蛋白质羰基、MDA和8-OHdG含量的影响(P<0.05)。

表3 配方乳中添加BPP对RV攻毒仔猪回肠形态及黏膜RV-IgM含量和抗氧化指标的影响

Table 3 Effects of BPP supplementation in formula milk on ileal morphology, and RV-IgM content and antioxidant indices in ileal mucosa in piglets challenged by RV

项目 Items	未添加BPP Without BPP supplementation		添加BPP BPP supplementation		P值 P-value
项目 Items	对照组 Control group	RV攻毒组 RV challenged group	BPP组 BPP group	RV攻毒组 RV challenged group	轮状病毒 RV	构树叶多糖 BPP	轮状病毒× 构树叶多糖 RV×BPP
RV特异性免疫球蛋白M RV-IgM/(μg/mg prot)	1.60±0.07^b	2.28±0.05^a	1.47±0.06^b	2.50±0.09^a	<0.001	0.488	0.019
绒毛高度 Villus height/μm	485.85±26.75^b	355.70±27.12^c	596.00±32.98^a	533.16±38.77^ab	0.007	<0.001	0.302
隐窝深度 Crypt depth/μm	238.94±23.57^b	359.47±28.93^a	213.53±12.49^b	254.19±16.07^b	0.013	<0.001	0.005
绒隐比 Villus height/crypt depth	2.13±0.12^b	1.05±0.15^c	2.83±0.06^a	2.61±0.10^a	<0.001	<0.001	0.001
总抗氧化能力 T-AOC/(U/mg prot)	0.37±0.02^b	0.27±0.02^c	0.49±0.02^a	0.44±0.03^a	0.002	<0.001	0.292
过氧化氢酶 CAT/(U/mg prot)	1.42±0.07^bc	1.35±0.08^c	1.76±0.06^a	1.62±0.07^ab	0.146	<0.001	0.622
超氧化物歧化酶 SOD/(U/mg prot)	108.60±5.45	99.97±3.00	114.09±4.22	113.16±6.89	0.360	0.082	0.459
谷胱甘肽过氧化物酶 GSH-Px/(mU/mg prot)	18.38±1.16	18.61±0.27	20.31±0.44	19.74±0.71	0.816	0.049	0.587
蛋白质羰基 Protein carbonyl/ (nmol/mg prot)	6.29±0.41^b	7.78±0.33^a	4.48±0.35^c	5.08±0.08^c	0.004	<0.001	0.178
丙二醛 MDA/(nmol/mg prot)	6.46±0.44^b	7.82±0.36^a	5.75±0.25^b	6.38±0.31^b	0.009	0.006	0.302
8-羟基脱氧鸟苷 8-OHdG/(ng/mg prot)	0.38±0.03^ab	0.42±0.02^a	0.33±0.02^bc	0.29±0.05^c	0.984	<0.001	0.107

2.3 配方乳中添加BPP对RV攻毒仔猪回肠黏膜紧密连接蛋白、黏蛋白和细胞凋亡相关基因表达的影响

由表4可知,RV攻毒显著提高了仔猪回肠黏膜Caspase-3和Bax mRNA相对表达量及Bax/Bcl-2(P<0.05)。配方乳中添加BPP显著提高了仔猪回肠黏膜MUC1、Occludin和Bcl-2 mRNA相对表达量(P<0.05),显著降低了回肠黏膜Bax mRNA相对表达量及Bax/Bcl-2(P<0.05);且在RV攻毒仔猪中,配方乳中添加BPP显著缓解了RV攻毒对回肠黏膜MUC1、Occludin、Caspase-3和Bax mRNA相对表达量及Bax/Bcl-2的影响(P<0.05)。

表4 配方乳中添加BPP对RV攻毒仔猪回肠黏膜紧密连接蛋白、黏蛋白和细胞凋亡相关基因表达的影响

Table 4 Effects of BPP supplementation in formula milk on expression of genes related to tight junction proteins, mucin and apoptosis in ileal mucosa in piglets challenged by RV

项目 Items	未添加BPP Without BPP supplementation			添加BPP BPP supplementation			P值 P-value
项目 Items	对照组 Control group	RV攻毒组 RV challenged group		BPP组 BPP group	RV攻毒组 RV challenged group		轮状病毒 RV	构树叶多糖 BPP	轮状病毒× 构树叶多糖 RV×BPP
黏蛋白1 MUC1	1.00±0.03^ab	0.79±0.04^b		1.03±0.11^ab	1.29±0.15^a		0.823	0.042	0.072
闭合蛋白Occludin	1.00±0.08^bc	0.63±0.10^c		1.27±0.05^ab	1.57±0.09^a		0.683	<0.001	0.002
半胱氨酸天冬氨酸蛋白酶-3 Caspase-3	1.00±0.06^b	1.37±0.08^a		1.00±0.09^b	1.19±0.07^b		0.002	0.288	0.263
B细胞淋巴瘤-2 相关X蛋白 Bax	1.00±0.04^b	1.39±0.10^a		0.88±0.08^b	1.01±0.02^b		0.002	0.002	0.071
B细胞淋巴瘤-2 Bcl-2	1.00±0.06^b	0.87±0.08^c	1.24±0.14^a		1.09±0.05^a	0.143		0.022	0.864
B细胞淋巴瘤-2相关 X蛋白/B细胞淋巴瘤-2 Bax/Bcl-2	1.00±0.06^b	1.60±0.11^a	0.73±0.10^c		0.93±0.05^bc	<0.001		<0.001	0.038

3 讨论

RV是引起幼龄动物(包括新生仔猪)严重腹泻和脱水的主要病原体之一,其感染通常伴随着肠道屏障功能的损伤^[1]。国内外以仔猪为对象的相关研究^[16-17]以及本课题组的前期研究^[18-19]表明,RV感染会诱导仔猪中重度腹泻,抑制生长,破坏肠道屏障功能,提高肠道的细胞凋亡,并降低肠道抗氧化能力。本试验也得到了类似的结果,但RV攻毒对仔猪回肠带来的负面影响程度不同,这可能源于RV对于不同肠段的影响存在差异。此外,本试验还发现,RV攻毒显著提高了仔猪回肠黏膜RV-IgM含量。免疫球蛋白M(IgM)是机体受抗原刺激后最先产生的抗体,其含量升高通常标志着发生了急性感染^[20-21]。以上结果说明,本试验成功构建了幼龄仔猪RV感染模型。

本团队前期研究显示,灌服BPP可以缓解氧化鱼油饲粮诱导的断奶大鼠生长抑制和腹泻的发生^[9]。本试验也发现类似结果,配方乳中添加BPP显著提高了RV攻毒仔猪ADG,显著降低了RV攻毒仔猪中重度腹泻发生率(从83.33%降低至58.33%)。腹泻往往伴随着营养物质消化吸收率的下降,进而导致生长迟缓,本试验中仔猪生长性能的改善与腹泻率的降低是一致的。不过,本研究发现,RV攻毒虽然对仔猪ADFI的影响并不显著,但却导致了严重的体重负增长,这提示RV感染引起的生长停滞并非主要源于食欲减退(厌食),而更多归因于腹泻导致的营养物质消化吸收障碍。这一推论在RV攻毒损伤回肠形态的结果中得到证实,继而直接减少了营养物质的吸收面积;而添加BPP显著逆转了这一趋势,从而在采食量无显著差异的情况下,保障了仔猪的生长性能。除了作为机体消化吸收的主要器官,肠道的屏障功能是宿主抵御外界病原入侵的第一道防线^[22]。由此推断,BPP缓解RV攻毒条件下的生长受阻和腹泻发生可能与其改善肠道健康(尤其是屏障功能)有关。

作为肠道屏障功能的重要组成,物理屏障和化学屏障是肠道黏膜抵御病原体直接接触和入侵上皮细胞的关键防线,它们协同作用以维持肠道组织的完整性与稳态^[23]。物理屏障主要由完整的肠道组织结构(如绒毛形态)、肠上皮细胞及其顶端的紧密连接蛋白(如Occludin)构成,其中的紧密连接蛋白能封闭细胞间隙,有效控制旁细胞通透性,防止病原体穿透^[22,24];化学屏障则主要由杯状细胞和上皮细胞分泌的黏蛋白(如MUC1)覆盖于上皮表面形成的黏液层组成,能够捕获病原微生物并阻止其黏附于上皮细胞表面^[25]。本试验中,除了改善肠道形态外,配方乳中添加BPP还可以缓解RV攻毒对仔猪回肠黏膜Occludin和MUC1 mRNA相对表达量的负面影响,这表明BPP能够通过维护肠道形态完整性、促进紧密连接蛋白和黏蛋白的合成,增强肠道黏膜的物理和化学屏障功能,从而缓解RV诱导的腹泻。此外,前人在环磷酰胺攻毒的黄羽肉鸡^[26]和采食氧化鱼油饲粮的大鼠^[9]研究中也得到了类似的结果。

肠道屏障功能的基础是肠道上皮细胞的存活情况(尤其是细胞凋亡),氧化应激是病毒感染导致细胞凋亡的重要机制之一^[27]。因此,本试验进一步分析了仔猪回肠黏膜细胞凋亡相关基因mRNA相对表达量和抗氧化相关指标,结果表明,配方乳中添加BPP显著缓解了RV攻毒对仔猪回肠黏膜Caspase-3和Bax mRNA相对表达量、Bax/Bcl-2及T-AOC、CAT活性和生物大分子过氧化产物(如羰基化蛋白质、MDA和8-OHdG)含量的负面影响。前人在体内外研究中发现,来源于构树叶或果实的多糖具有抗氧化能力^[7,9];且BPP处理可缓解氧化鱼油饲粮诱导的大鼠肠道黏膜细胞凋亡^[9],缓解对乙酰氨基酚攻毒诱导的小鼠肝脏细胞凋亡^[28]。因此,BPP改善RV攻毒仔猪肠道屏障功能与其增强抗氧化能力和肠道上皮细胞活性有关。

4 结论

本试验成功建立了RV感染仔猪模型,并以此为基础研究发现,配方乳中添加BPP可以缓解RV诱导的仔猪生长抑制和中重度腹泻。这一保护作用主要归因于BPP能有效提高仔猪回肠黏膜抗氧化能力,抑制RV诱导的细胞过度凋亡,改善肠道形态,进而维持肠道黏膜的完整性和屏障功能。

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