喻正旺，周忠新

中鏈脂肪酸抗菌和誘導(dǎo)防御肽表達(dá)的功能及其在仔豬飼料中的應(yīng)用

喻正旺，周忠新

農(nóng)業(yè)動(dòng)物遺傳育種與繁殖教育部重點(diǎn)實(shí)驗(yàn)室/生豬健康養(yǎng)殖協(xié)同創(chuàng)新中心/華中農(nóng)業(yè)大學(xué)動(dòng)物營養(yǎng)與飼料科學(xué)系，武漢 430070

近年,越來越多的研究表明，中鏈脂肪酸（MCFAs）抵抗病原菌是哺乳動(dòng)物先天防御系統(tǒng)的重要組成部分，而且MCFAs也能夠誘導(dǎo)人、豬和雞內(nèi)源性防御肽的表達(dá)，MCFAs的這些新功能尚未引起重視。MCFAs還和飼用有機(jī)酸或飼用植物精油具有協(xié)同抗菌增效作用，可以減少這些活性物質(zhì)的使用量。相比于長鏈脂肪酸，日糧中添加MCFAs能顯著地提高動(dòng)物機(jī)體內(nèi)氧氣消耗量和線粒體呼吸速率，但產(chǎn)生活性氧自由基少，特別適合幼齡動(dòng)物腸代謝和肝代謝所需的快速能量供應(yīng)特點(diǎn)。日糧添加低濃度MCFAs（0.1%—0.5%，質(zhì)量比）能顯著提高新生或斷奶仔豬存活率、粗蛋白粗脂肪消化率、飼料轉(zhuǎn)化率，調(diào)節(jié)腸道菌群和改善腸上皮結(jié)構(gòu)，進(jìn)而促進(jìn)生長?；贛CFAs的上述功能，將MCFAs與飼用有機(jī)酸或植物精油復(fù)配制備成微囊顆粒，可能是其用于仔豬抗生素替代品的尚佳方式。

中鏈脂肪酸；先天防御系統(tǒng)；協(xié)同抗菌；防御肽；仔豬

0 引言

瑞典雀巢公司基于大量醫(yī)學(xué)和獸醫(yī)學(xué)文獻(xiàn)分析后對(duì)抗生素促生長機(jī)理進(jìn)行了概述，稱“抗生素對(duì)人和動(dòng)物的促生長效應(yīng)主要是減少了病原菌感染及其伴隨的炎癥響應(yīng)造成的熱量負(fù)擔(dān)（因?yàn)樵诹己眯l(wèi)生狀況下不能觀察到抗生素的促生長效應(yīng)）”[1]。中鏈脂肪酸( medium-chain fatty acids，MCFAs)不僅具有良好的抑菌或殺菌、抗病毒和抗寄生蟲作用[2-4]，而且能夠改善腸道健康[5-7]和提高飼料消化率[8-9]。近年新的研究發(fā)現(xiàn)，MCFAs抵抗病原菌是幼齡動(dòng)物先天防御系統(tǒng)的重要組成部分，而且MCFAs能夠誘導(dǎo)人和動(dòng)物體內(nèi)宿主防御肽(host defensin peptides，HDPs)的表達(dá)[10-12]，被認(rèn)為是一種良好的免疫增強(qiáng)劑。早前報(bào)道的綜述主要針對(duì)MCFAs的殺菌或抑菌活性[8,13-14]，以及MCFAs對(duì)仔豬生產(chǎn)性能的影響[3,8,15-19]，均未涉及MCFAs誘導(dǎo)宿主防御素表達(dá)的內(nèi)容。本文主要綜述了MCFAs在哺乳動(dòng)物先天防御中的重要作用、誘導(dǎo)宿主防御肽表達(dá)、協(xié)同抗菌增效、代謝優(yōu)勢(shì)機(jī)理幾個(gè)方面的新進(jìn)展及其在仔豬抗生素替代品中的應(yīng)用前景。本文還介紹了微囊化技術(shù)在避免中鏈脂肪酸難聞氣味、減少添加量和延長腸道作用時(shí)間中的優(yōu)勢(shì)。

1 中鏈脂肪酸具有良好體外抑菌或殺菌作用，化學(xué)性質(zhì)穩(wěn)定

脂肪酸是重要的有機(jī)化工和精細(xì)化工原料，目前從天然動(dòng)植物油脂經(jīng)水解、精餾生產(chǎn)的脂肪酸占脂肪酸總量的4/5以上，是世界脂肪酸的主要來源[20]。脂肪酸根據(jù)碳鏈的長度分為短鏈、中鏈和長鏈脂肪酸3種，通常把含有6—12個(gè)碳原子的直鏈飽和脂肪酸稱為中鏈脂肪酸。MCFAs資源來源廣，自然界中天然存在的MCFAs都是偶數(shù)碳長，包括己酸（C6）、辛酸（C8）、癸酸（C10）和月桂酸（C12），主要存在于椰子油（含60%）[21-23]、棕櫚油（含8%）、萼距花屬植物油中[24]。MCFAs具有良好的抑菌或殺菌作用，很早就被用于飼料（尤其用于青貯飼料）和食品防腐中[4]。體外試驗(yàn)已經(jīng)證明MCFA及其單甘油酯都能夠抑制或殺死致病菌、病毒和寄生蟲[3, 25]?？偟膩碇v，中鏈脂肪酸（己酸、辛酸、癸酸和月桂酸）及其脂肪酸甘油一酯(辛酸甘油酯、癸酸甘油酯和月桂酸甘油酯)和長鏈不飽和脂肪酸（棕櫚烯酸、棕櫚油酸、油酸、順式-8-十八碳烯酸和亞油酸）抑菌活性較強(qiáng)，脂肪醇（正辛醇、正葵醇和月桂醇）次之，長鏈飽和脂肪酸（肉豆蔻酸、軟脂酸和硬脂酸）抑菌效果相對(duì)較弱[26-27]。MCFAs主要作用于細(xì)菌的細(xì)胞膜，其兩親性的化學(xué)結(jié)構(gòu)可以破壞細(xì)菌細(xì)胞膜的結(jié)構(gòu)，導(dǎo)致細(xì)胞內(nèi)容物流出和細(xì)胞裂解，從而導(dǎo)致細(xì)菌死亡[28-30]，這種機(jī)制也使得致病菌很難對(duì)其產(chǎn)生耐藥性[31-32]。

值得注意的是，中鏈脂肪酸（辛酸、葵酸、月桂酸）與有機(jī)弱酸（乙酸、乳酸、蘋果酸、檸檬酸）對(duì)O157:H7具有極強(qiáng)的協(xié)同殺菌作用，葵酸與檸檬酸的協(xié)同殺菌能力最強(qiáng)；例如，無殺菌效應(yīng)的0.125mmol·L-1的葵酸（約0.002%）與無殺菌效應(yīng)的0.125mmol·L-1的乳酸、0.125mmol·L-1蘋果酸、0.125 mmol·L-1檸檬酸（約0.0015%）分別組合后能顯示極強(qiáng)的協(xié)同殺菌效應(yīng)，其殺菌活力的Log CFU值在協(xié)同前后的變化分別為2、3、6，如果提高組合的濃度，協(xié)同殺菌能力更強(qiáng)[33]。中鏈脂肪酸（辛酸，癸酸和月桂酸）與食用植物精油（香芹酚，丁香酚，β-間苯二酸，反式肉桂醛，百里酚和香蘭素）復(fù)合，對(duì)O157:H7的殺菌作用同樣大大增強(qiáng)[34]。采用辛酸和牛至精油的組合處理沙門氏菌、單核細(xì)胞增生性李斯特菌、大腸桿菌和金黃色鏈球菌時(shí)，發(fā)現(xiàn)辛酸和牛至精油表現(xiàn)出良好的協(xié)同效應(yīng)[35]。比例為2:1:1:5:2:2的辛酸、香芹酚、癸酸、肉桂醛、丁香酚、己酸復(fù)合配方對(duì)大腸桿菌、沙門氏菌和金黃色葡萄球菌的抑菌性能高且在模擬胃腸液環(huán)境中同樣具有良好的抑菌作用[36]。斷奶是養(yǎng)豬生產(chǎn)中最具挑戰(zhàn)性和關(guān)鍵性的階段之一[37]。仔豬斷奶后通常有一個(gè)生長延滯期，主要是因?yàn)槲竷?nèi)鹽酸和胰酶分泌不足導(dǎo)致消化能力低，以及日糧和環(huán)境因素改變等應(yīng)激導(dǎo)致的采食量下降和腹瀉[38]。日糧中加入弱的有機(jī)酸降低胃腸道pH值能一定程度緩解這個(gè)問題，常用的有機(jī)弱酸主要是檸檬酸、甲酸、丙酸、乳酸、富馬酸、苯甲酸等[39]。體外模擬盲腸系統(tǒng)證實(shí)辛酸鈉可以顯著減少大腸桿菌和沙門氏菌的數(shù)量[40]，通過斷奶仔豬口服鼠傷寒沙門氏菌或產(chǎn)腸毒素大腸桿菌構(gòu)建的兩個(gè)實(shí)驗(yàn)?zāi)Ｐ?，證實(shí)了從椰子油中提取的中鏈脂肪酸鹽混合物能夠減小沙門氏菌或大腸桿菌等條件致病菌在腸道定植的活性[41]。因此MCFAs在預(yù)防和治療仔豬腹瀉方面將有較大的應(yīng)用前景，且與有機(jī)酸或植物精油復(fù)合使用殺菌效果可能更好。

2 中鏈脂肪酸抵抗病原菌是哺乳動(dòng)物先天防御系統(tǒng)的重要組成部分

脂質(zhì)的抗菌作用在20世紀(jì)60年代前后被發(fā)現(xiàn)，但近年來人們才開始認(rèn)識(shí)到脂肪酸是許多生物抵抗病原菌的先天防御系統(tǒng)的重要組成部分，尤其是在皮膚和黏膜表面的防御中，包括哺乳動(dòng)物、兩棲動(dòng)物、軟體動(dòng)物、植物、藻類[26, 28, 42-43]。哺乳動(dòng)物母乳[24, 42]、皮膚[26, 44-45]、粘膜[42]中都存在高含量的中鏈飽和脂肪酸和長鏈不飽和脂肪酸，它們是這些組織抵御病原微生物最活躍的抗菌劑，其作用比以前想象的更為重要[26, 42, 44-47]。例如人的皮膚中每平方厘米含有10—15μg的游離脂肪酸，其中月桂酸 (C12)、肉豆蔻酸 (C14)、棕櫚酸 (C16)、sapienic acid (C16:1n-10)、 cis-8-octadecenoicacid (C18:1n-10)含量最豐富[28]。測試細(xì)菌對(duì)丙酮提取的前臂皮膚的敏感性試驗(yàn)發(fā)現(xiàn)，化膿性鏈球菌和金黃色葡萄球菌在脂質(zhì)減少的情況下的存活時(shí)間明顯長于未經(jīng)處理的皮膚[48]。動(dòng)物母乳中含有大量抗菌的MCFAs（己酸C6、辛酸C8、葵酸C10、月桂酸C12）和LCFAs（主要是油酸C18:1、亞油酸C18:2、亞麻酸C18:3），其中中鏈脂肪酸占乳脂的比例高，兔（58%）、大鼠（58%）、馬（48.1%）、山羊（34.7%）、奶牛（20.7%）、人（11.7%）、豬（4.1%）[24, 49]。以低脂牛奶為唯一牛奶來源的兒童發(fā)生急性胃腸道疾病的可能性比服用全脂牛奶的兒童高5倍[50]。高脂肪牛奶飲食喂養(yǎng)可以減少李斯特菌在大鼠腸黏膜的定植[51]。由此可見，MCFAs在皮膚和黏膜屏障功能中發(fā)揮重要作用，是哺乳動(dòng)物先天防御系統(tǒng)的重要組成部分。

3 中鏈脂肪酸能夠誘導(dǎo)人、豬和雞內(nèi)源防御肽的表達(dá)

宿主防御肽(Host defensin peptides, HDPs)是小于50個(gè)氨基酸的短肽，一般帶正電荷，具有兩親性，廣泛存在于植物界和動(dòng)物界[52-53]。HDPs是先天免疫系統(tǒng)的重要組成部分，對(duì)細(xì)菌、真菌、原生生物和多種病原體都具有直接的抗菌活性[54-56]。此外，HDPs還具有強(qiáng)大免疫調(diào)節(jié)活性，可以抑制炎癥反應(yīng)和促進(jìn)傷口愈合[57-60]。例如含有豬宿主防御肽（PR-39/pBD-1）的重組質(zhì)?？烧{(diào)節(jié)仔豬腸道的先天性和適應(yīng)性免疫反應(yīng)，可以降低仔豬的腹瀉率[61]。

近年的研究表明，MCFAs可以誘導(dǎo)人和動(dòng)物體內(nèi)HDPs的表達(dá)。國外ZENG 等報(bào)道認(rèn)為，碳鏈長度為3—10的脂肪酸（包含奇數(shù)碳和偶數(shù)碳）能顯著誘導(dǎo)體外培養(yǎng)的豬腸上皮細(xì)胞中至少3種防御素基因的表達(dá)，但其誘導(dǎo)機(jī)制和動(dòng)物體內(nèi)效應(yīng)不得而知[62]；這些脂肪酸也能誘導(dǎo)雞巨噬細(xì)胞和單核細(xì)胞中防御素基因的表達(dá)[10]。JIANG 等也報(bào)道，短鏈、中鏈、長鏈脂肪酸都能不同程度地誘導(dǎo)人體內(nèi)抗菌肽LL-37基因和蛋白的表達(dá)[63]。WANG等在探索辛酸（C8）和葵酸（C9）對(duì)腸上皮屏障功能的影響時(shí)，發(fā)現(xiàn)辛酸（C8）和葵酸（C9）可促使內(nèi)源性防御肽pBD-1、pBD-2的表達(dá)顯著升高，其作用機(jī)制為辛酸（C8）和葵酸（C9）減弱了經(jīng)典組蛋白脫乙酰基酶途徑的活性，促進(jìn)了啟動(dòng)子pBD-1和pBD-2上組蛋白3賴氨酸9（H3K9）的乙?；瑥亩鰪?qiáng)了PBD-1和PBD-2基因表達(dá)[12]?；贖DPs在先天免疫和適應(yīng)性免疫中的重要作用，近來一些外源性的HDPs正在被開發(fā)和利用，但體外合成的HDPs還存在穩(wěn)定性較差、易在動(dòng)物消化道及胃中發(fā)生降解的問題[64]。BECHINGER等[65]和CHEUNG等[66]報(bào)道指出使用外源HDPs成本較高且仍然存在耐藥風(fēng)險(xiǎn)，并且還可能會(huì)影響內(nèi)源性HDPs在先天性免疫中的保護(hù)功能。所以通過MCFAs調(diào)控內(nèi)源性HDPs的合成與分泌已成為一種用于疾病控制和預(yù)防的有前途的抗生素替代方法[67]。

4 中鏈脂肪酸不同于長鏈脂肪酸的消化、吸收和代謝特點(diǎn)

MCFAs水解能力和吸收速度是長鏈脂肪酸(Long Chain Fatty Acids，LCFAs)的6倍，代謝速度是其10倍，能夠快速為腸細(xì)胞和肝代謝提供能量[3, 68]。利用同位素標(biāo)記技術(shù)比較仔豬對(duì)中鏈脂肪酸和長鏈脂肪酸的吸收效果和氧化效果，結(jié)果表明辛酸的吸收和氧化速率要顯著高于油酸[69]。其主要原因是MCFAs比LCFAs分子量小、呈極性且水溶性較好，對(duì)膽鹽和胰酶的依賴性低，更容易被水解和吸收；MCFAs吸收后不依賴肉毒堿的轉(zhuǎn)運(yùn)，主要以游離形式進(jìn)入門靜脈，能夠自由通過線粒體的雙層膜進(jìn)入線粒體氧化，進(jìn)而快速為機(jī)體供能，而LCFAs必須與腸細(xì)胞中的脂肪酸結(jié)合蛋白（FABP）結(jié)合，轉(zhuǎn)運(yùn)到滑面內(nèi)質(zhì)網(wǎng)，重新酯化形成甘油三酯，然后與載脂蛋白結(jié)合形成乳糜微粒，進(jìn)入到淋巴系統(tǒng)，通過血液循環(huán)被運(yùn)往機(jī)體肌肉、肝臟、脂肪組織細(xì)胞[68,70]。體外研究表明，中鏈脂肪酸可以顯著提高肝細(xì)胞氧氣的消耗量、NAD(P)H的水平[71]及氧化丙酮和乳酸的活性[70]。用葵酸（C10）或月桂酸（C12）處理的C2C12肌管產(chǎn)生的ROS要顯著低于肉豆蔻酸或棕櫚酸處理組，且耗氧量比肉豆蔻酸（C14）或棕櫚酸(C16)處理組高[72]。喂食MCFAs的小鼠肌細(xì)胞比LCFAs組線粒體氧化能力顯著增強(qiáng)，活性氧自由基的產(chǎn)生顯著降低[73-74]，這與體外研究結(jié)果一致。對(duì)其機(jī)理的解釋方面，喂食MCFA的小鼠試驗(yàn)表明，MCFA會(huì)誘導(dǎo)ω氧化基因Cyp4a10和Cyp4a14的表達(dá)，增加二羧基脂肪酸的產(chǎn)量，激活過氧化物酶體增殖物激活受體（peroxisome proliferators- activated receptors，PPARs），進(jìn)而激活脂肪酸在微體中的ω氧化途徑、在線粒體和過氧化物酶體中的β氧化途徑，從而加速M(fèi)CFA的氧化供能水平[74]。由此可見，MCFAs在體內(nèi)具有消化吸收快、代謝快、產(chǎn)生活性氧自由基少的特點(diǎn)，特別適合幼齡動(dòng)物腸代謝和肝代謝所需的快速能量供應(yīng)特點(diǎn)。

5 中鏈脂肪酸對(duì)仔豬存活率、生長性能、營養(yǎng)物質(zhì)表觀消化率和腸道微生物的影響

MCFAs在新生或斷奶仔豬的研究報(bào)道較多[75]，在母豬、蛋雞、肉雞、牛飼料中也有一些零星報(bào)道[76-79]。這些研究表明，MCFAs及其甘油酯可以調(diào)節(jié)畜禽營養(yǎng)代謝、提高畜產(chǎn)品品質(zhì)，在動(dòng)物生產(chǎn)中使用MCFAs是發(fā)展綠色畜產(chǎn)品生產(chǎn)的有效途徑之一。前人關(guān)于中鏈脂肪酸的添加濃度和形式以及對(duì)仔豬存活率、生長性能、營養(yǎng)物質(zhì)表觀消化率和腸道微生物的影響的研究在表1中進(jìn)行了總結(jié)。

HANCZAKOWSKA等基于252頭新生仔豬的試驗(yàn)結(jié)果表明，日糧中添加0.1%（1g·kg-1）的辛酸（C8）或葵酸（C10）可使84日齡體重增加14%—22%，平均日增重增加15%—23%，料肉比降低20%—30%，粗蛋白或粗脂肪的表觀消化率提高5%，粗纖維的表觀消化率提高10%—13%，死亡率下降8.2%—11.3%，無氮浸出物的表觀消化率變化不顯著；同時(shí)，添加0.1%的辛酸（C8）或葵酸（C10）也都使腸絨毛高度、隱窩深度、及絨毛高/隱窩深度比值顯著增加，有害菌產(chǎn)氣莢膜梭菌的數(shù)量顯著減少，葵酸的效應(yīng)更顯著[80]。在斷奶仔豬飼料中添加0.1%的中鏈脂肪酸和植物精油復(fù)合物（桉樹油+辛酸+葵酸），顯著提高了仔豬日增重和采食量，并且與抗生素組、ZnO組沒有差異，同時(shí)也提高了干物質(zhì)、粗蛋白、鈣、磷、能量和氨基酸消化率[81]。HANCZAKOWSKA等基于326頭斷奶仔豬試驗(yàn)，在酸化劑（0.5%的甲酸和丙酸）的基礎(chǔ)上再添加0.2%的辛酸（C8）或葵酸（C10）可以進(jìn)一步提高84日齡體重和平均日增重，進(jìn)一步降低料肉比，粗纖維表觀消化率進(jìn)一步提高11%—14%（干物質(zhì)、粗蛋白、粗脂肪消化率也有提高）[82]。0.3%的中鏈脂肪酸和有機(jī)酸混合物（MCFA +甲酸鈣+乳酸鈣+檸檬酸）可以替代仔豬日糧中的氧化鋅，顯著提高仔豬采食量、促進(jìn)動(dòng)物生長，同時(shí)還可以顯著增加直腸和回腸中乳酸桿菌的數(shù)量并顯著降低沙門氏菌和腸球菌數(shù)量[83]。而日糧中添加高濃度（8%）的中鏈脂肪酸（60%辛酸和40%葵酸）可以提高飼料轉(zhuǎn)化效率和氨基酸的消化率，但差異不顯著。

綜上所述，高濃度(8%)的中鏈脂肪酸可以提高飼料的轉(zhuǎn)化效率以及能量和氨基酸的消化率，但差異不顯著。低濃度（0.1%—0.5%）的中鏈脂肪酸可顯著提高新生或斷奶仔豬存活率、營養(yǎng)物質(zhì)消化率、飼料轉(zhuǎn)化率、改善腸道健康，促進(jìn)生長。中鏈脂肪酸對(duì)生長性能提升效果較好的為辛酸（C8）和葵酸(C10)。體外抗菌效果方面，0.002%的葵酸和0.0015%的檸檬酸組合對(duì)O157:H7的殺菌能力最強(qiáng)，0.004%葵酸和0.006%-間苯二酸組合對(duì)O157:H7的殺菌能力最強(qiáng)[33-34]。體內(nèi)應(yīng)用效果方面，0.1%的桉樹油-辛酸-葵酸組成的復(fù)合物、0.3%的MCFA-甲酸鈣-乳酸鈣-檸檬酸組成的復(fù)合物和0.2%的中鏈脂肪酸（辛酸或葵酸）與0.5%的有機(jī)酸（甲酸和丙酸）組成的復(fù)合物均可以達(dá)到替代仔豬飼料中氧化鋅的作用。不同的動(dòng)物或相同動(dòng)物的不同生長階段，以及養(yǎng)殖場管理方式和環(huán)境等都是影響中鏈脂肪酸組合效果的重要因素，特別是不同的養(yǎng)殖場對(duì)組合效應(yīng)的報(bào)道結(jié)果缺乏一致性，這可能是不同養(yǎng)殖場的不同管理和環(huán)境導(dǎo)致的。

6 微囊化技術(shù)是提高中鏈脂肪酸溶解度和生物利用度，避免難聞氣味的有效方法

微囊化技術(shù)是將小的固體顆粒，液滴或氣體包裹在涂層中的一種技術(shù)，已經(jīng)被用于食品工業(yè)、化妝品及制藥等多個(gè)領(lǐng)域，它可以保護(hù)活性成分免受外部環(huán)境的影響，掩蓋難聞的氣味，還可以將活性成分運(yùn)送到動(dòng)物體內(nèi)特定的作用靶點(diǎn)[87]。MCFAs難溶于水、有難聞氣味、刺激縮膽囊素釋放而減少采食量[3]。MCFAs濃度隨著胃腸道逐漸降低，在仔豬日糧中添加包被的中鏈脂肪酸，中鏈脂肪酸在胃腸道各部位的濃度顯著高于對(duì)照組（添加相同濃度的未包被中鏈脂肪酸）[88]，這表明利用包被技術(shù)減少中鏈脂肪酸的用量及延長中鏈脂肪酸在胃腸道的作用時(shí)間的可行性，將有利于降低仔豬的腹瀉率。中鏈脂肪酸和有機(jī)酸或精油具有協(xié)同抗菌作用，在斷奶仔豬飼料中添加中鏈脂肪酸和植物精油復(fù)合物制成的微囊可以達(dá)到替代日糧中氧化鋅和抗生素的作用[82]。體外胃腸道模擬試驗(yàn)表明，月桂酸和百里香酚制成的微粒可以被運(yùn)輸?shù)侥c道后段以防止斷奶仔豬腹瀉[89]。日糧中添加有機(jī)酸和中鏈脂肪酸制成的脂質(zhì)微囊，顯著提高了生長豬的生產(chǎn)性能[90]。目前國內(nèi)鮮有關(guān)于包被中鏈脂肪酸用作飼料添加劑替代抗生素的報(bào)道。

表1 基礎(chǔ)仔豬日糧中添加一定濃度的中鏈脂肪酸對(duì)仔豬生產(chǎn)性能、營養(yǎng)物質(zhì)表觀消化率、腸道微生物及結(jié)構(gòu)和仔豬死亡率的影響

BW:體重；FCR:飼料轉(zhuǎn)化率；ADFI：平均日采食量；ADG:平均日增重；DM；干物質(zhì)

BW: weight; FCR: feed conversion rate; ADFI: average daily food intake; ADG: average daily weight gain; DM; Dry matter

7 小結(jié)

中鏈脂肪酸是哺乳動(dòng)物母乳、皮膚、粘膜先天防御系統(tǒng)的重要組成部分，中鏈脂肪酸誘導(dǎo)人、豬和雞內(nèi)源性防御肽表達(dá)現(xiàn)象的發(fā)現(xiàn)，是對(duì)已有中鏈脂肪酸體外抗菌功能認(rèn)知的有益補(bǔ)充，這些新功能將促進(jìn)中鏈脂肪酸在仔豬飼料抗生素替代品開發(fā)中的應(yīng)用。日糧中添加低濃度（0.1%—0.5%）的中鏈脂肪酸可提高新生或斷奶仔豬存活率、營養(yǎng)物質(zhì)消化率、飼料轉(zhuǎn)化率，改善腸道健康，促進(jìn)仔豬生長。中鏈脂肪酸與植物精油或有機(jī)酸具有協(xié)同抗菌增效功能，將其混合制備成微囊顆粒，能很好地提高其溶解性，避免難聞氣味，提高生物利用度。

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Functions of Antibacterial and Inducing Defense Peptide Expression of Medium-Chain Fatty Acid and Its Application in Piglet Feeds

YU ZhengWang, ZHOU ZhongXin

Key Lab of Agricultural Animal Genetics/Breeding and Reproduction of Ministry of Education/Department of Animal Nutrition and Feed Science, Huazhong Agriculture University, Wuhan 430070

In recent years, more and more studies have shown that medium-chain fatty acid (MCFAs) resistance to pathogenic bacteria is an important component of innate defense system of mammals, and MCFAs can also induce expressions of endogenous host defense peptides (HDPs) in human, pig and chicken. However, these new functions of MCFAs have not attracted much attention. MCFAs also have a synergistic antibacterial synergistic effect with feeding organic acids or feeding plant essential oils, which can reduce the use of these active substances. In addition, compared with long-chain fatty acids, the addition of MCFAs in the diet can significantly increase the oxygen consumption and mitochondrial respiration rate in the body of animals, but it produces less reactive oxygen species, which is in line with the characteristics of rapid energy supply required by intestinal metabolism and liver metabolism in young animals. Adding low concentration of MCFAs (0.1%-0.5%, mass ratio) to the diet can significantly increase the survival rate of newborn or weaned piglets, the digestibility of crude protein and crude fat as well as the feed conversion rate, regulate the intestinal flora, and improve the intestinal epithelial structure, thus promoting the growth of animals. Based on the above advantages of MCFAs, mixing MCFAs with forage organic acid or plant essential oil to prepare coated particles may be a good way to use it as a substitute for antibiotics in piglets.

medium chain fatty acid; innate defense system; host defense peptide; synergistic antibiotics; piglets

10.3864/j.issn.0578-1752.2021.13.017

2020-05-31；

2021-04-07

“十三五”國家重點(diǎn)研發(fā)計(jì)劃(2016YFD0501210)、中央高?；究蒲袠I(yè)務(wù)費(fèi)專項(xiàng)基金資助（2662018BY017)

喻正旺，E-mail：1575800877@qq.com。通信作者周忠新，E-mail：zhongxinzhou@mail.hzau.edu.cn

（責(zé)任編輯 林鑒非）