Chinese Journal of Animal Nutrition >

2024 , Vol. 36 >Issue 3: 1927 - 1941

DOI: https://doi.org/10.12418/CJAN2024.168

RESEARCH PAPER

Effects of Dietary Fiber Supplementation in Diet on Growth Performance and Intestinal Health of Broiler Chickens: A Meta-Analysis

  • HE Wenfeng ,
  • ZHANG Mi ,
  • YANG Yajin ,
  • FAN Xiao ,
  • LIU Lili ,
  • GUO Aiwei , *
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  • College of Life Science, Southwest Forestry University, Kunming 650224, China
*professor, E-mail:

Received date: 2023-10-15

  Online published: 2024-03-13

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Abstract

The aim of this study was to explore the effects of dietary fiber supplementation in diet on growth performance and intestinal health of broiler chickens by a Meta-analysis. By searching the Web of Science, PubMed, CNKI and Wanfang databases for experimental studies on the effects of dietary fiber on the growth performance and intestinal morphology of broilers from years 2007 to 2022, a total of 27 articles were selected, totaling 5 310 broilers. The Review Manager 5.3 software was used to analyze indicators such as average daily gain (ADG), final body weight (FBW), average daily feed intake (ADFI) and ileal villus height (VH), crypt depth (CD), villus height/crypt depth (VH/CD) and gizzard relative weight (GRW) of broiler chickens. The results showed that compared with the control group, dietary fiber supplementation in diet significantly increased the ADG [merge effect (MD)=1.01, 95% confidence interval (95% CI): 0.29 to 1.72, P=0.006 00], FBW (MD=45.05, 95% CI: 16.68 to 73.42, P=0.002 00), ileal VH (MD=36.58, 95% CI: 14.22 to 58.94, P=0.001 00) and GRW (MD=0.16, 95% CI: 0.11 to 0.21, P<0.000 01) of broiler chickens, significantly decreased the F/G (MD=-0.04, 95% CI: -0.06 to -0.01), P=0.008 00) of broiler chickens, and dietary fiber supplementation in diet had no significant effects on ADFI (MD=0.29, 95% CI: -0.59 to 1.17, P=0.520 00), ileal CD (MD=5.51, 95% CI -1.83 to 12.86, P=0.140 00) and VH/CD (MD = 0.06, 95% CI: -0.01 to 0.14, P=0.090 00) of broiler chickens. The subgroup analysis showed that the insoluble dietary fiber (IDF) supplementation in diet significantly increased the ADG (MD=1.34, 95% CI: 0.56 to 2.12, P=0.000 70), ileal VH (MD=50.37, 95% CI 24.22 to 76.51, P=0.000 20) and VH/CD (MD=0.25, 95% CI: 0.17 to 0.32, P<0.000 01), and significantly decreased the F/G (MD=-0.04, 95% CI: -0.06 to -0.02, P=0.000 60) of broiler chickens; the soluble dietary fiber (SDF) supplementation in diet had no significant effects on ADFI (MD=0.71, 95% CI: -0.68 to 2.10, P=0.320 00), ADG (MD=0.69, 95% CI: -0.65 to 2.03, P=0.310 00), F/G (MD=-0.04, 95% CI: -0.09 to 0.01, P=0.090 00), ileal VH (MD=17.00, 95% CI: -5.51 to 39.50, P=0.140 00), CD (MD=3.01, 95% CI: -3.10 to 9.13, P=0.330 00) and VH/CD (MD=-0.27, 95% CI: -0.79 to 0.29, P=0.360 00) of broiler chickens. In conclusion, when the crude fiber content in broiler chickens’ diet from 1.43% to 6.17%, the dietary fiber supplementation in diet can improve the growth performance and intestinal health of broiler chickens. Compared with SDF, IDF has a greater effect on improving the growth performance and intestinal health of broiler chickens.

Key words： dietary fiber; broiler chickens; growth performance; intestinal health; Meta-analysis

Cite this article

HE Wenfeng , ZHANG Mi , YANG Yajin , FAN Xiao , LIU Lili , GUO Aiwei . Effects of Dietary Fiber Supplementation in Diet on Growth Performance and Intestinal Health of Broiler Chickens: A Meta-Analysis[J]. Chinese Journal of Animal Nutrition, 2024 , 36(3) : 1927 -1941 . DOI: 10.12418/CJAN2024.168

膳食纤维(dietary fiber,DF)一词最早由澳大利亚科学家Hipsley于1953年提出的,DF是动物不能消化的植物细胞壁组分,主要包括纤维素、半纤维素和木质素[1],迄今为止DF的定义仍存在争议,国际上还没有达成普遍的共识。目前DF普遍接受的定义为“DF是不能被人类内源性消化酶所消化的所有多糖和木质素”。动物营养学家对DF则采用生理学或化学上的定义,从生理学上定义为DF是“抵抗动物酶降解的食物成分”,从化学上定义为DF是非淀粉多糖(NSP)和木质素的总和[2]。DF根据溶解性可分为可溶性膳食纤维(soluble dietary fiber,SDF)和不溶性膳食纤维(insoluble dietary fiber,IDF),根据在肠道微生物的发酵与否可分为可发酵膳食纤维(fermentable fiber,FF)和不可发酵膳食纤维(non-fermentable fiber,NFF)。SDF主要包括果胶、树胶和部分半纤维素等,由于其高的持水性和黏性,可延缓胃肠道的排空速度,此外,SDF在肠道微生物发酵后产生短链脂肪酸(SCFAs);而IDF主要包括纤维素、半纤维素、木质素以及几丁质等,IDF可增加肠道内容物在肠道运输速率和保水能力,缩短不易消化食物在结肠中的发酵时间,增加粪便体积等[3-4]。
20世纪70年代后,为了提高家禽的生长性能,家禽养殖尤其是肉鸡生产中普遍采用高能量、高蛋白质、低纤维的配合饲料,极大地提高了家禽的生产水平,而DF被认为是一种抗营养因子,没有引起动物营养学家的关注[5]。因此,在相当长的一段时间内,在肉鸡饲粮中尽可能限制纤维性饲料的添加,商业配合饲料中通常最多含有2%~3%的粗纤维(CF)[6]。随着全球饲料中禁抗的呼声越来越高,动物营养学家又开始关注DF对动物肠道健康的影响。Desai等[7]用剥夺DF的小鼠模型研究表明,长期或间接性剥夺小鼠饮食中的DF,则导致肠道菌群利用宿主分泌的黏蛋白作为营养源,造成小鼠肠道黏液层变薄,肠道屏障损伤,而用鼠柠檬梭杆菌(Citrobacter rodentium)感染小鼠,发现剥夺DF组小鼠肠道中有更多病原菌进入肠上皮并促成致命性结肠炎;结果提示,DF不足造成的肠道菌群降解结肠黏膜屏障并增加病原体敏感性;而富含DF组的小鼠具有完整的屏障功能,肠道病原体易感性降低,提示DF具有保护肠道健康的作用。此外,也有研究也发现,低DF或剥夺DF饮食会增加机体炎症性肠炎(IBD)、腹泻等慢性疾病发生的几率[8-9]。
近年来,在家禽上的许多研究证实,添加适量的DF可以改善肉鸡生长性能、饲料转化效率、肠道发育、肠道黏膜形态,通过促进肠道上皮细胞的增殖来促进肠道的发育,增强肠道免疫或降低肠道炎症,维持肠道微生物多样性等方面来调控肠道健康[2,10]。但DF是否是家禽的必需营养素仍存在很多争议,为了深入阐明DF对肉鸡生长性能和肠道健康的影响规律,本研究对已发表的关于DF对肉鸡生长发育及肠道健康方面影响的文章进行了Meta分析,为DF在肉鸡生产中的合理使用提供科学依据。

1 材料与方法

1.1 文献检索

利用Web of Science (WOS)、PubMed、中国知网、万方等数据库检索文献,英文数据库检索词包括:dietary fiber or dietary fibre、broiler chickens or broilers、performance;中文数据库检索词包括:膳食纤维、肉鸡、生长性能;将检索词在数据库进行自由组合后检索并收集全部DF与肉鸡相关的文献。论文发表时间在2007年1月至2022年12月,共检索到1 077篇文献,按照纳入及排除标准筛选(图1),去除重复文献,排除综述性文献、会议文献,通过筛选检索到文献的标题、摘要和全文后,共有27篇文献符合Meta分析的要求,总计5 310羽肉鸡,平均每个研究197羽肉鸡,纳入本次Meta分析中(表1)。在纳入Meta分析的文献中,DF添加量在0.01%~10.00%,添加的DF源主要包括大豆壳(SH)、甜菜浆(SBP)、芦笋修剪物(TABP)、麦麸(WB)、柑橘渣(CP)、花生荚(PP)、向日葵壳(SFH)、橄榄粉(OM)、果聚糖(FRT)、微粉化不溶性纤维(MIF)、燕麦壳(OH)、苹果渣(AP)、草莓渣(SP)、低聚木糖(XOS)、菊粉(INU)、阿拉伯树胶(AS)、木质素(LI)、稻壳(RH)、纤维素(CEL)、羧甲基纤维素(CMC)、菊苣(FC)等。纳入分析的27篇文献中,试验饲粮中CF含量在1.43%~6.17%,中性洗涤纤维(NDF)含量在5.60%~13.84%,酸性洗涤纤维(ADF)含量在1.60%~6.03%。
图1 文献筛选流程

Fig.1 Literature selection process

表1 纳入文献特征汇总

Table 1 Summary of features of included literature

编号
Number		 作者及年份
Author and
publication year		 纤维源
Fiber
source		 添加量
Added
amount/%		 饲粮纤维水平
Dietary fiber
level/%		 试验天数
Experimental
day/d		 肉鸡
Broilers		 试验鸡数量
Number of
experimental
broilers		 分析指标
Analysis indexes
1 Jiménez-Moreno
等(2013)[11]		 OH(IDF)
SBP(SDF)		 5.00 CF:3.42
CF:2.89		 18 Ross 308 42
42		 ADG、ADFI、F/G
2 Nopparatmaitree
等(2022)[12]		 TABP(SDF) 3.00 CF:4.69 35 Ross 308 80 ADG、ADFI、F/G、VH、
CD、VH/CD
3 Shang(1)等
(2020)[13]		 WB(IDF) 3.00 CF:2.96;
NDF:11.86		 42 Arbor Acre 56 ADG、ADFI、F/G
4 Sarbaz等(2018)[14] PP(IDF) 5.00 CF:5.53;NDF:13.84;
ADF:6.03		 42 Ross 308 80 ADG、ADFI、F/G、GRW
5 Kimiaeitalab
等(2017)[15]		 SFH(IDF) 3.00 CF:4.40;NDF:10.30;
ADF:5.70		 21 Ross 308 70 ADG、ADFI、F/G、VH、
CD、VH/CD、GRW
6 Sateri等(2017)[16] OM(IDF) 6.00 CF:2.60 42 Ross 308 30 ADG、FBW、ADFI、
F/G、GRW
7 Zhao等(2013)[17] FRT(SDF) 0.25 CF:2.83 31 Ross 308 240 ADG、ADFI、F/G、GRW
8 Rezaei等(2011)[18] MIF(IDF) 0.45 CF:2.33 42 Ross 308 80 ADG、ADFI、F/G、VH、CD、
VH/CD、GRW
9 González-Alvarado
等(2010)[19]		 SBP(SDF)
OH(IDF)		 3.00 CF:2.07;NDF:6.30;ADF:2.25
CF:2.38;NDF:7.00;ADF:2.50		 42 Cobb 500 60
60		 ADG、FBW、ADFI、F/G、GRW
10 Jiménez-Moreno
等(2009)[20]		 SBP(SDF) 3.00 CF:2.07;NDF:5.60;ADF:1.60 21 Cobb 500 108 ADG、ADFI、F/G、GRW
11 Mourão等(2008)[21] CP(SDF) 5.00 CF:3.50 34 Cobb 350 35 ADG、FBW、ADFI、F/G
12 González-Alvarado
等(2007)[22]		 OH(IDF) 3.00 CF:3.30 21 Cobb 500 144 ADG、ADFI、F/G、GRW
13 Bai等(2019)[23] LJP(SDF) 1.00 CF:3.18 42 Arbor Acre 72 ADG、FBW、ADFI、F/G
14 Colombino等
(2020)[24]		 AP(SDF)
SP(SDF)		 3.00 CF:3.20
CF:3.30		 35 Ross 308 60
60		 ADG、ADFI、F/G、VH、
CD、VH/CD
15 Singh等(2021)[25] XOS(SDF) 0.01 CF:2.24;NDF:8.05;
ADF:3.57		 42 Cobb 500 32 ADG、FBW、ADFI、F/G、
VH、CD、VH/CD、GRW
16 Moreno-Mendoza
等(2021)[26]		 INU(SDF) 1.50 CF:4.43 40 Ross 308 70 ADG、ADFI、F/G
17 Al-Baadani等(2022)[27] AS(SDF) 0.50 CF:2.93;NDF:10.56;ADF:4.78 35 Ross 308 72 ADG、ADFI、F/G、
VH、CD、VH/CD
18 Liebl等(2022)[28] LI(IDF)
SH(IDF)		 0.80
1.60		 CF:2.23
CF:2.33		 36 Ross 308 1 260
1 260		 VH、CD、VH/CD、GRW
19 Shang(2)等(2020)[29] WB(IDF) 3.00 CF:2.95;IDF:12.65;SDF:1.83 42 Arbor Acre 48 FBW、VH、CD、VH/CD、GRW
20 Tejeda(a)等(2021)[3] CEL(IDF)
SH(IDF)		 4.00 CF:4.00
CF:1.43		 21 Cobb 500 72
72		 VH、CD、VH/CD、GRW
21 Sozcu(2019)[30] LI(IDF) 0.10 CF:1.98 35 Ross 308 180 FBW、VH、CD、VH/CD
22 Sabour等(2018)[31] SBP(SDF)
RH(IDF)		 3.00 CF:2.45
CF:3.34		 42 Ross 308 65
65		 ADG、ADFI、F/G、
VH、CD、VH/CD
23 Li等(2018)[32] INU(SDF)
WB(IDF)		 2.00
10.00		 CF:2.93;NDF:12.44;ADF:4.73
CF:3.45;NDF:11.06;ADF:4.38		 35 Ross 308 240
240		 FBW、VH、CD、VH/CD
24 Rahmatnejad
等(2015)[33]		 CEL(IDF)
CMC(SDF)		 4.00 CF:6.17
CF:2.48		 21 Ross 308 40
40		 VH、CD、VH/CD
25 Liu等(2013)[34] FC(SDF) 6.00 CF:4.16 27 Ross 308 64 VH、CD
26 Kurul等(2020)[35] SH(IDF) 4.00 CF:3.51;NDF:9.51;ADF:4.25 21 Ross 308 56 ADG、FBW、ADFI、F/G、GRW
27 Tejeda(b)等(2020)[36] SF(IDF)
SH(IDF)		 4.00 CF:3.96
CF:1.43		 20 Cobb 500 72
72		 ADG、FBW、ADFI、F/G、
VH、CD、VH/CD、GRW

OH:燕麦壳 oat hulls;SBP:甜菜浆 sugar beet pulp;TABP:芦笋修剪物 trimmed asparagus by-products;WB:麦麸 wheat bran;PP:花生荚 peanut pod;SFH:向日葵壳 sunflower hulls;OM:橄榄粉 olive meal;FRT:果聚糖 fructan;MIF:微粉化不溶性纤维 micronized insoluble fiber;CP:柑橘渣 citrus pulp;LJP:海藻粉 laminaria japonica powder;AP:苹果渣 apple pomaces;SP:草莓渣 strawberry pomaces;XOS:低聚木糖 xylo-oligosaccharides;INU:菊粉 inulin;AS:阿拉伯树胶 acacia senegal;LI:木质素 lignocellulose;SH:大豆壳 soybean husk;CEL:纤维素 cellulose;RH:稻壳 rice husk;CMC:羧甲基纤维素 carboxymethyl cellulose;FC:菊苣 forage chicory;SF:纯化纤维素 solka-floc;SDF:可溶性膳食纤维 soluble dietary fiber;IDF:不溶性膳食纤维 insoluble dietary fiber;CF:粗纤维 crude fiber;NDF:中性洗涤纤维 neutral detergent fiber;ADF:酸性洗涤纤维 acid detergent fiber;ADG:平均日增重 average daily gain;ADFI:平均日采食量 average daily feed intake;F/G:料重比 feed/gain;VH:绒毛高度 villus height;CD:隐窝深度 crypt depth;VH/CD:绒毛高度/隐窝深度 villus height/crypt depth;GRW:肌胃相对重量 gizzard relative weight;FBW:终末体重 final body weight;Ross 308:罗斯308;Arbor Acre:爱拔益加;Cobb 500:科宝500。

1.2 纳入文献标准

纳入文献试验设计为完全随机对照试验,试验中的每个组设有5个及以上重复,研究对象为肉鸡,研究用的饲粮以玉米-豆粕型为主。Meta分析考察的肉鸡生长性能指标包括平均日增重(ADG)、终末体重(FBW)、平均日采食量(ADFI)和料重比(F/G),肠道组织形态指标包括回肠绒毛高度(VH)、隐窝深度(CD)、绒毛高度/隐窝深度(VH/CD)及肌胃相对重量(GRW)。

1.3 文献筛选标准

文献中明确试验动物为肉鸡,排除蛋鸡和火鸡的文献,排除试验方法不明确、缺少对照组、试验重复数低于5,测定指标或指标数据不全以及与同类文章差异过大的文献,排除会议文献、综述性文献,排除数据不全、重复报道的文献。

1.4 数据提取和处理

每篇文献提取的基础数据包括该研究的作者、论文发表年份、试验的重复数、每个重复肉鸡的数量、试验天数、纤维源的添加水平等指标,并在文中明确纤维源是SDF或IDF。

1.5 统计与分析

运用Review Manager 5.3软件进行Meta分析,对纳入研究采用固定效应模型(I2<50%且P>0.05)或者随机效应模型(I2≥50%或P<0.05)进行异质性分析,计算合并效应值(MD)、95%置信区间(95%CI)及相应显著性概率(P值)。若存在异质性,则进行亚组分析,绘制森林图,对纳入文献的结果指标进行发表偏倚分析并绘制漏斗图,运用Stata 12.0软件进行Egger线性回归分析。

2 结果与分析

2.1 饲粮中添加DF对肉鸡生长性能的影响

2.1.1 ADG

饲粮中添加DF对肉鸡ADG的影响Meta分析见图2,结果表明,与不添加DF的对照组相比,试验组95%CI落在无效线的右侧且没有与无效线相交,提示肉鸡的ADG与纳入DF之间具有显著的相关性(P<0.05),表明饲粮中添加DF显著提高了肉鸡ADG(MD=1.01,95%CI为0.29~1.72,P=0.006 00);并对纤维类型进行了亚型分析,结果表明SDF和IDF对肉鸡ADG的影响存在差异,饲粮中添加IDF可显著提高了肉鸡的ADG(MD=1.34,95%CI为0.56~2.12,P=0.000 70),而添加SDF对肉鸡ADG的影响不显著(MD=0.69,95%CI为-0.65~2.03,P=0.310 00)。
图2 饲粮中添加DF对肉鸡ADG的影响

Experimental:试验组 experimental group;Control:对照组 control group;Mean Difference:均值差 mean difference;Study or Subgroup:研究或亚组;Mean:平均值;SD:标准差 standard deviation;Total:样本数 sample number;Weight:权重;IV:逆方差 inverse variance;Random:随机;95%CI:95%置信区间 95% confidence interval;Subtotal:亚组总体;Heterogeneity:异质性检验;Test for overall effect:总效应量检验;Test for subgroup differences:亚组差异检验;df:自由度 degree of freedom;Favours [experimental]:试验组获益;Favours [control]:对照组获益。下图同 the same as below。

Fig.2 Effects of DF supplementation in diet on ADG of broiler chickens

2.1.2 FBW

饲粮中添加DF对肉鸡FBW的影响Meta分析见图3,纳入饲粮中添加DF与肉鸡FBW影响的相关研究。结果表明,饲粮中添加DF可显著改善肉鸡FBW(I2=99%,MD=45.05,95%CI为16.68~73.42,P=0.002 00)。
图3 饲粮中添加DF对肉鸡FBW的影响

Fig.3 Effects of DF supplementation in diet on FBW of broiler chickens

2.1.3 ADFI

饲粮中添加DF对肉鸡ADFI的影响Meta分析见图4(P<0.05,I2=96%),采用随机效应模型分析表明,与对照组相比,饲粮中添加DF对肉鸡ADFI无显著影响(MD=0.29,95%CI为-0.59~1.17,P=0.520 00);亚组分析结果显示,饲粮中添加IDF(MD=-0.01,95%CI为-1.11~1.09,P=0.980 00)和SDF(MD=0.71,95%CI为-0.68~2.10,P=0.320 00)均对肉鸡的ADFI无显著影响,表明饲粮中添加DF总体上对肉鸡ADFI的影响不显著。
图4 饲粮中添加DF对肉鸡ADFI的影响

Fig.4 Effects of DF supplementation in diet on ADFI of broiler chickens

2.1.4 F/G

饲粮中添加DF对肉鸡F/G的影响Meta分析见图5(P<0.05,I2>50%),采用随机效应模型进行分析表明,与对照组相比,试验组的总效应量小于对照组,在整个试验期肉鸡饲粮中添加DF显著降低了F/G(MD=-0.04,I2=99%,95%CI为-0.06~-0.01,P=0.008 00);亚组分析结果显示,饲粮中添加IDF显著降低了肉鸡的F/G(MD=-0.04,95%CI为-0.06~-0.02,P=0.000 60),而添加SDF对肉鸡F/G无显著影响(MD=-0.04,95%CI为-0.09~0.01,P=0.090 00)。
图5 饲粮中添加DF对肉鸡F/G的影响

Fig.5 Effects of DF supplementation in diet on F/G of broiler chickens

2.2 饲粮中添加DF对肉鸡肠道形态的影响

2.2.1 回肠VH

饲粮中添加DF对肉鸡回肠VH的影响Meta分析见图6(P<0.05,I2>50%),采用随机效应模型进行分析表明,饲粮中添加DF显著提高了肉鸡的回肠VH(MD=36.58,95%CI为14.22~58.94,P=0.001 00),亚组分析结果表明,饲粮中添加IDF极显著提高了肉鸡的回肠VH(MD=50.37,95%CI为24.22~76.51,P=0.000 20),而饲粮中添加SDF对肉鸡的回肠VH无显著影响(MD=17.00,95%CI为-5.51~39.50,P=0.140 00)。
图6 饲粮中添加DF对肉鸡回肠VH的影响

Fig.6 Effects of DF supplementation in diet on ileal VH of broiler chickens

2.2.2 回肠CD

饲粮中添加DF对肉鸡回肠CD的影响Meta分析见图7(P<0.05,I2>50%),采用随机效应模型进行分析表明,饲粮中添加DF对肉鸡的回肠CD无显著影响(MD=5.51,95%CI为-1.83~12.86,P=0.140 00);亚组分析结果表明,饲粮中添加IDF(MD=7.26,95%CI为-2.38~16.91,P=0.140 00)和SDF(MD=3.01,95%CI为-3.1 ~9.13,P=0.330 00)对肉鸡的回肠CD无显著影响。
图7 饲粮中添加DF对肉鸡回肠CD的影响

Fig.7 Effects of DF supplementation in diet on ileal CD of broiler chickens

2.2.3 回肠VH/CD

饲粮中添加DF对肉鸡回肠VH/CD的影响Meta分析见图8(P<0.05,I2>50%),采用随机效应模型分析表明,饲粮中添加DF对肉鸡的回肠VH/CD无显著影响(MD=0.06,95%CI为-0.01~0.14,P=0.090 00);亚组分析结果表明,饲粮中添加IDF显著提高了肉鸡的回肠VH/CD(MD=0.25,95%CI为0.17~0.32,P<0.000 01),饲粮中添加SDF对肉鸡的回肠VH/CD无显著影响(MD=-0.27,95%CI为-0.79~0.29,P=0.360 00)。
图8 饲粮中添加DF对肉鸡回肠VH/CD的影响

Fig.8 Effects of DF supplementation in diet on ileal VH/CD of broiler chickens

2.3 饲粮中添加DF对肉鸡肌胃发育的影响

饲粮中添加DF对肉鸡GRW的影响Meta分析见图9,纳入肉鸡饲粮中添加DF与GRW的相关研究。结果显名,饲粮中添加DF可显著提高肉鸡GRW(MD=0.16,95%CI为0.11~0.21,P<0.000 01),提示饲粮中添加DF可促进肉鸡肌胃的发育。
图9 饲粮中添加DF对肉鸡GRW的影响

Fig.9 Effects of DF supplementation in diet on GRW of broiler chickens

2.4 发表偏倚分析

对纳入文献进行发表偏倚分析结果见表2和图10,结局指标ADG、FBW、ADFI、F/G、VH、VH/CD及GRW的P值分别为0.849 00、0.561 00、0.816 00、0.225 00、0.946 00、0.152 00、0.132 00,即P>0.05,显示纳入的指标不存在发表偏倚,其中CD的P值为0.041 00,即P<0.05,显示纳入的指标存在发表偏倚。结局指标ADG、FBW、ADFI、F/G、VH、CD、VH/CD及GRW纳入文献的效应指标散点图显示,图中散点基本位于中线两侧,对称性较好,说明本研究选择的文献研究样本量大,结果准确性高,发表偏倚程度较小,选取的论文具有代表性,结果的可靠性高。
表2 发表偏倚Egger检验

Table 2 Publication bias Egger test

项目
Items		 平均
日增重
ADG		 终末体重
FBW		 平均日
采食量
ADFI		 料重比
F/G		 绒毛高度
VH		 隐窝深度
CD		 绒毛高度/
隐窝深度
VH/CD		 肌胃相
对重量
GRW
95%置信区间
95%CI		 -5.273,
4.381		 -10.975,
6.221		 -5.354,
4.262		 -12.349,
3.080		 -13.690,
14.616		 -28.111,
-0.620		 -1.634,
9.740		 -2.033,
14.096
P值
P-value		 0.849 00 0.561 00 0.816 00 0.225 00 0.946 00 0.041 00 0.152 00 0.132 00
图10 饲粮中添加DF对肉鸡生长性能影响的漏斗图

A:平均日增重 average daily gain (ADG);B:终末体重 final body weight (FBW);C:平均日采食量 average daily feed intake (ADFI);D:料重比 feed/gain (F/G);E:绒毛高度 villus height (VH);F:隐窝深度 crypt depth (CD);G:绒毛高度/隐窝深度 villus height/crypt depth (VH/CD);H:肌胃相对重量 gizzard relative weight (GRW)。

Fig.10 Funnel plot of effects of DF supplementation in diet on growth performance of broiler chickens

3 讨论

肉鸡生长性能是由肠道组织形态、肠道营养物质消化吸收、肠道发育、肠道微生物等参数所表现出的综合表型特征,研究表明,改善肠道组织形态和促进器官发育可以增加养分的吸收,表现在生长性能的增加和肠道健康[37,38]。而DF一方面由于其组成、理化特性、颗粒大小、添加水平的差异,另一方面考虑到家禽遗传特性(慢速肉鸡或快速肉鸡)、生理状况、饲粮能量、蛋白质、脂肪水平等的差异[20,36,39-40],加上家禽消化道独特性,添加不同来源的DF对家禽生长性能和肠道健康的影响存在差异,尤其是DF的溶解性或发酵特性。研究表明,添加适量的IDF时会改善肉鸡生长性能和肠道健康,将燕麦壳和大豆壳等IDF(3%~5%)添加饲粮中,可显著降低肉鸡的F/G(2%),提高FBW(2%~5%)[40⇓-42]。而添加SDF在对家禽生长性能的影响与IDF存在明显的差异,研究表明,添加SDF可提高肉鸡的F/G,在饲粮中添加3%的高甲基化果胶,可使肉鸡F/G显著提高(28%)[43],添加0.3%的可溶性纤维如瓜尔胶时,肉鸡的F/G提高了5%,但与对照组差异不显著[44],这与本研究Meta分析的结果不尽相同,这一方面与饲粮中添加量有关系,另一方面还与SDF的黏性和发酵特性有关,可溶性DF果胶是一种在肠道快速发酵和具有黏性的DF,其可能在肠道快速发酵导致后肠微生物失调和养分利用效率下降,最终导致肉鸡的生长性能降低。而IDF或低发酵DF可改善肠道的组织形态,促进肠道发育,从而改善肉鸡的生长性能。以上研究表明,肉鸡对饲粮中DF的需求理论上应该包含一定比例的IDF和一定比例的SDF,而且SDF和IDF有一个适宜比例(SDF/IDF),目前在家禽上关于适宜IDF/SDF研究缺乏相关的证据,今后应该进一步开展此方面的研究工作,为在家禽生产中科学、合理利用纤维性物质提供科学依据。
家禽为了维护正常的消化生理和肠道蠕动,需要在饲粮中提供一定量的DF[22],而DF在家禽胃肠道中发挥作用取决于其化学结构、粒度和添加量[39,45]。研究表明,饲粮中添加DF后家禽肠道对其产生快速的适应性变化,如改变肠道长度、VH、CD以及食糜通过肠道速率和肠道重量[3,5,46]。肠道VH和上皮细胞排列的改善被认为是可以增加营养吸收,含2.8%~9.0% CF的饲粮(等氮等能)饲喂火鸡,结果表明,中等纤维饲喂时小肠所有绒毛数量和长度增加[47],而高纤维饲粮对家禽是不利的,在饲粮中添加7.5%的豌豆皮或SBP会增加肉鸡小肠黏膜表面的磨损,绒毛缩短,同时会增加黏液的分泌[48]。此外,高DF会导致肉鸡对蛋白质的消化吸收降低和氨基酸内源性损失,在饲粮中添加8%的纤维素会导致肉鸡肠道中蛋白质和氨基酸的损失和死亡率增加[49],会降低消化酶活性和营养物质的消化率[11],这可能也是饲喂高DF的弊端之一,在这种情况下,应该通过营养策略在高DF饲粮中适当增加一些功能性氨基酸以抵消这种变化,确保家禽最佳的生长速度。但目前尚不清楚肉鸡饲粮中DF的阈值,DF的类型、来源及饲料配方参数都可能会影响这一阈值[11],今后应该加强此方面的研究。本研究Meta分析的结果表明,添加适量的DF会改善肉鸡肠道组织形态,促进肠道发育,而过量则对肠道发育是不利的。
研究表明,家禽消化道能够迅速对食物组成的变化做出适应性调整,DF会影响家禽消化道的长度和重量,尤其是肌胃变化最明显[50],研究表明,DF会刺激肌胃肌肉活动,其结果会导致肌胃重量增加,一个发育良好的肌胃拥有更强壮的肌肉组织和更强的研磨能力,可改善肠道的蠕动能力,进而降低病原微生物在肌胃下肠段定植的风险,从而降低和缓解沙门氏菌和球虫[51]等引起的肠道疾病,最终提高养分的利用效率、肠道健康和家禽生长性能。O’Dell等[52]研究发现,当饲粮缺乏DF时,肉鸡肌胃发育不良,而且缺乏DF与家禽养殖过程中雏鸡出现的腺胃炎有很大的关联,当肉鸡饲喂包含完整谷物成分的饲粮时,腺胃扩张的发生率降低,同时证实了家禽腺胃-肌胃区域的正常发育依赖于饲粮中的结构性成分,主要是DF[53]。Jiménez-Moreno等[54]研究表明,在饲粮中添加3%的SBP或燕麦壳会增加肉鸡GRW,在36日龄肉鸡饲粮中,将燕麦壳或SBP的添加量增加到5%,结果提高了肌胃的重量,并降低了肌胃pH。这与本研究Meta分析结果一致,即饲粮中添加DF可显著提高肉鸡GRW。一般情况下,饲料在肌胃的滞留时间在0.5~1.0 h,当添加DF后饲料在肌胃的滞留时间会增加到2.0 h[55]。研究表明,添加6%的木屑可降低肉鸡F/G(1.1%),但与对照组差异不显著,同时会增加腺胃和肌胃的重量,降低小肠的相对重量[40]。同样,添加3%的燕麦壳和大豆壳可增加肉鸡肌胃的重量,并改善了饲料转化率[22]。肌胃重量的增加是由于DF的存在使饲料在肌胃存留时间延长而导致体积增加的结果。纤维素、木质素和阿拉伯木聚糖等DF的存在也可以调节小肠、胰腺和盲肠的重量,这可以改善营养物质的总肠道表观保留率[22,41,56-57]。研究表明,在1~4周龄火鸡饲粮中添加6%和9%的CF,火鸡对粗蛋白质、粗脂肪和总能的消化率降低,而在第8周龄时,这种情况消失了[47],这种变化是由于胃肠道及时补偿DF变化的能力,从而提高了营养物质的利用能力。添加3%麦麸的鸡表现出GRW和胰淀粉酶和胰蛋白酶活性的增加,这与营养物质消化率的增加有关[29],这种适量的不可消化DF如纤维素、木质素可上调了机体消化酶活性,导致其淀粉、蛋白质等营养物质的消化率增加[58],从而适应含有DF的饲粮。
以上研究表明,肉鸡对含DF的饲粮有一个逐步的适应过程,添加DF后肉鸡通过增加肌胃重量和肠道长度,通过延长食物在肌胃停留时间,刺激消化酶的分泌,改变肠道微生物等来逐步适应DF,肉鸡对DF的适应也存在一个剂量-时间效应。此外,肉鸡在不同生长阶段对DF的需求存在一个阈值,即肉鸡对饲粮中DF的需求有一个最低值和最大值,由于DF组成的复杂性以及来源、理化性质的不同,肉鸡饲粮中DF的阈值可能存在差异。因此,今后应用现代分子生物学、组学技术与传统动物营养学技术手段相结合,进一步加强DF和IDF、FF和NFF以及SDF/IDF、FF/NFF对肉鸡生长性能、肠道健康的调控机制以及在肉鸡不同阶段DF的最适添加量和阈值,为DF在家禽生产中的应用提供科学依据。

4 结论

① 饲粮CF含量在1.43%~6.17%,添加DF显著提高了肉鸡FBW、ADG及回肠VH、GRW;显著降低了F/G,而对ADFI及回肠CD和VH/CD的影响差异不显著。
② 饲粮CF含量在1.43%~6.17%,添加IDF显著提高了肉鸡ADG及回肠VH、VH/CD,显著降低了F/G;饲粮CF含量在2.07%~4.69%,添加SDF对肉鸡ADFI、ADG、F/G及回肠VH、CD、VH/CD的影响不显著。
③ 为了维持肉鸡正常的生理功能、生长性能和肠道健康,在饲粮中需要有一定量的DF,而且IDF和SDF对肉鸡生长性能和肠道健康的影响存在差异;此外,肉鸡对DF的需求可能存在一个阈值。

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