动物营养学报    2020, Vol. 32 Issue (1): 36-41    PDF    
植物提取物对高精料饲粮下反刍动物瘤胃功能、微生物区系和炎症反应的调控效果
张芮铭 , 田可 , 何天乐 , 董国忠     
西南大学动物科技学院, 重庆市牧草与草食家畜重点实验室, 重庆 400716
摘要: 为提高反刍动物生产性能,满足其营养需求,实际生产中生产者常常使用高精料饲粮饲喂反刍动物。反刍动物长期饲以高精料饲粮会导致瘤胃微生物区系改变,引起瘤胃发酵和代谢紊乱,进而影响动物健康。植物提取物具有调节瘤胃微生物区系、改善瘤胃发酵和代谢的作用。本文综述了植物提取物对高精料饲粮下反刍动物瘤胃功能、微生物区系和炎症反应的影响及作用效果。
关键词: 植物提取物    高精料饲粮    反刍动物    瘤胃功能    微生物区系    炎症反应    
Regulation Effects of Plant Extracts on Rumen Function, Microflora and Inflammatory Response in Ruminants under High-Concentrate Diet
ZHANG Ruiming , TIAN Ke , HE Tianle , DONG Guozhong     
College of Animal Science and Technology, Chongqing Key Laboratory of Forage and Herbivores, Southwest University, Chongqing 400716, China
Abstract: In order to improve the performance of ruminants and meet their nutritional needs, producers often use high-concentrate diets in practical ruminant production. Long-term feeding of high-concentrate diets can lead to changes in the rumen microflora and disorders in rumen fermentation and metabolism, which in turn affects animal health. Plant extracts have the effects of regulating the rumen microflora, improving rumen fermentation and metabolism. This paper reviewed the effects of plant extracts on rumen function, microflora and inflammatory response in ruminants under high-concentrate diets.
Key words: plant extracts    high-concentrate diets    ruminants    rumen function    microflora    inflammatory response    

在实际生产中, 为提高反刍动物生产性能, 生产者通常会增加饲粮中的精料比例来满足营养需求。动物长期采食高精料饲粮时, 瘤胃中碳水化合物快速发酵产生大量乳酸及短链脂肪酸(SCFA), 从而引起瘤胃pH下降与代谢紊乱, 进而造成一系列不良影响与并发症, 如采食量下降、蹄叶炎、肝脓肿等[1-4]。当瘤胃pH降低到5.2~5.8且每日持续3 h以上时, 即发生亚急性瘤胃酸中毒(SARA)[5]。内毒素(即脂多糖, LPS)是革兰氏阴性菌细胞壁组成成分, 能够渗透胃肠道屏障[6]。瘤胃pH剧烈的降低会引起大量的革兰氏阴性菌死亡, 从而释放出LPS。反刍动物发生SARA时, 瘤胃屏障功能被破坏, 消化道上皮释放大量LPS与组胺并被吸收进入血液循环[1], 导致外周血LPS浓度升高, 使细胞免疫处于主导作用, 促进了炎性因子的分泌, 打破了促炎性细胞因子和抗炎性细胞因子之间的平衡, 使动物长期处于免疫应激状态, 进而引发全身炎症反应[7-8], 当LPS累积到一定程度时甚至会引发LPS血症[9-10]。全身性炎症反应可使机体重新分配更多的营养素用于合成免疫物质, 造成反刍动物生产性能下降[11]

饲用抗生素如莫能霉素的使用可以通过促进瘤胃中丙酸生成进而改善瘤胃发酵[12], 然而, 由于抗生素的耐药性, 加上其残留问题对环境的污染及人类健康的威胁, 迫切需要寻找抗生素替代物。大量研究表明, 植物提取物可以调节反刍动物瘤胃发酵[13-14]。植物提取物是从植物中获取的, 具有一种或者多种生物学功能的物质。植物提取物富含生物活性物质, 具有抗菌、抗氧化、提高动物机体抗病力等功能, 在饲粮中添加可以提高畜禽免疫力、提升畜禽的生产性能、改善畜产品品质[15-16]。目前, 对植物提取物作用于反刍动物的研究主要集中在改善瘤胃发酵、调节瘤胃微生物区系、减少甲烷排放等方面[17-19]。本文着重综述植物提取物在高精料饲粮条件下改善瘤胃代谢功能和微生物区系以及降低炎症反应的效果, 为反刍动物生产提供参考。

1 植物提取物对反刍动物瘤胃pH及SCFA组成的调控

瘤胃pH和SCFA的浓度及组成比例是衡量瘤胃发酵的重要指标, 受精料组成和比例、唾液分泌量、瘤胃上皮对SCFA的吸收能力等诸多因素的综合调控[20-21]

研究发现, 饲粮中添加植物提取物有升高瘤胃pH的趋势。孙福昱等[22]发现, 在荷斯坦奶牛精料中加入5%(干物质基础)的海带粉可以提升瘤胃pH, 改善瘤胃酸性环境。此外, 郭长征[20]研究发现, 在高精料饲粮中添加100 mg/kg槲皮素可提高山羊瘤胃pH。

添加植物提取物可以调控瘤胃SCFA的组成。研究发现, 在荷斯坦奶牛精料中添加0.4%(干物质基础)的茴香粉可提高瘤胃液丙酸浓度, 降低乙酸与丙酸的比值(乙丙比)[21]。Karamnejad等[23]研究发现, 在绵羊高精料饲粮中按干物质基础添加21%的石榴皮可以降低瘤胃液乙酸浓度, 增加丙酸浓度, 并降低乙丙比。Neubauer等[24]的研究显示, 与未添加组相比, 在荷斯坦牛干奶期高精料饲粮中添加植物源性化合物(主要活性成分来源于薄荷、百里香、迷迭香和丁香)后瘤胃液可以表现出更低的乙丙比。红色山茱萸(ROD)是一种天然灌木, 富含花青素、槲皮素等生物活性物质, 在肉牛高精料饲粮中添加30 g/kg(干物质基础)的ROD可在一定程度上降低瘤胃液乙丙比[25]。随着荷斯坦奶牛精料中辣椒提取物(主要成分为辣椒素)剂量的增加, 瘤胃液乙酸比例线性降低, 丙酸比例有上升趋势, 乙丙比降低[26]。Balcells等[27]研究发现, 在母牛高精料饲粮中添加300 mg/kg植物黄酮类化合物可在不影响动物平均日增重和饲料转化率的条件下降低瘤胃液中乙酸浓度, 这可能是黄酮类化合物促进了瘤胃液中消耗乙酸的微生物的增殖, 同时提高了丙酸的浓度, 使乙丙比降低, 从而改善瘤胃发酵并降低SARA的不良影响。

2 植物提取物对反刍动物炎症反应的调控

反刍动物采食高精料饲粮会引起外周血中LPS浓度的提高[28], 进入血液的LPS通过循环系统运输至全身。由于肝脏消除LPS毒性的作用有限, 大量的LPS刺激肝脏巨噬细胞释放肿瘤坏死因子-α(TNF-α)、白细胞介素-1(IL-1)和白细胞介素-6(IL-6)等促炎细胞因子, 进而刺激肝脏产生大量急性期蛋白(APP), 包括血清淀粉样蛋白(SAA)、结合珠蛋白(Hp)、LPS结合蛋白(LPB)等[29]。研究表明, 饲喂高精料饲粮会导致反刍动物出现结肠炎症, 且白细胞介素-1β(IL-1β)、IL-6和Toll样受体3(TLR3)的表达量随高精料饲粮饲喂天数的增加呈线性增加[30]

相关研究表明, 植物提取物可以缓解高精料饲粮条件下反刍动物发生SARA的症状, 提高机体免疫功能。De Nardi等[31]研究表明, 在未怀孕荷斯坦奶牛的高精料饲粮中添加100 g/d富含多酚(主要成分为黄酮类)的植物精油可以降低瘤胃液中LPS浓度, 同时降低血液中SAA、LBP、Hp的浓度, 进而减弱炎性反应。在分娩前后(22±7) d的荷斯坦奶牛高精料饲粮中添加1 g/d的混合精油(主要成分为百里酚、丁香酚和香草醛等)可以降低瘤胃液中LPS浓度, 同时Hp、C-反应蛋白(CRP)浓度与对照组相比也有显著降低[32]。Humer等[33]发现, 在诱导奶牛发生SARA的高精料饲粮中加入植物源性化合物(主要活性物质来源于薄荷、百里香), 可以显著降低瘤胃液中LPS和组胺的浓度, 减弱炎症反应, 缓解SARA的不良影响。研究发现, 在母牛饲粮(精料比例80%)中添加丁香酚可以降低血浆中Hp浓度[34]; 在安格斯牛高精料饲粮中添加1 600 mg/(d·头)肉桂醛可以在试验期的前28 d降低血液中SAA和LBP的浓度[35]

3 植物提取物对反刍动物瘤胃微生物区系的影响

瘤胃中存在着细菌、原生动物、真菌、古细菌, 是一个极其复杂的生态系统。营养物质的消化利用受瘤胃微生物种类与比例的影响, 而饲粮则是影响瘤胃微生物组成的关键因素[36]。因此, 维持稳定、健康的瘤胃微生物区系对反刍动物的生产性能具有重要作用。

瘤胃细菌主要分为纤维降解菌、淀粉降解菌、乳酸产生菌及乳酸利用菌等。由于纤维分解菌不耐受低水平pH, 因此, 随着精料比例的不断提升, 反刍动物瘤胃pH的降低会抑制纤维分解菌的生长[37-38]。研究表明, 高精料饲粮会减少反刍动物消化道中微生物组成的多样性[39]。在高精料饲粮条件下, 瘤胃pH降低, 适应于酸性条件下生长的微生物如普雷沃氏菌属(Prevotella)和乳酸杆菌属(Lactobacillus)会大量繁殖, 而降解纤维的微生物如溶纤维丁酸弧菌(Butyrivibro fibrisolvens)由于不耐受低pH, 数量会明显降低。这不仅会造成反刍动物对粗饲料消化率的降低, 还会降低动物采食量, 影响机体健康。

已有文献表明, 在反刍动物饲粮中添加植物性添加剂可以调控瘤胃微生物区系[40]。Zotti等[41]发现, 饲粮中添加400 mg/kg混合精油(主要成分为蓖麻油酸和腰果壳液)可以显著降低瘤胃中总的原生动物数量, 产琥珀酸丝状杆菌的数量有上升趋势, 在一定程度上缓解高精料饲粮对瘤胃微生物区系的不良影响。牛链球菌(Streptococcus bovis)是一种淀粉利用菌, 与其他主要瘤胃细菌相比更容易产生多糖类生物膜, 是主要的乳酸产生菌[26]。Ishii等[42]的研究发现, 在高精料饲粮中添加与有机酸混合的扁柏醇能够降低瘤胃中牛链球菌的数量, 提高产琥珀酸丝状杆菌的数量, 同时还可减弱瘤胃胀气产生的不良影响。有研究表明, 在高精料饲粮中添加2 g/kg(干物质基础)的植物单宁(来源于栗树和白坚木)可以改善荷斯坦阉牛瘤胃微生物组成, 减少普雷沃氏菌属的丰富度, 有利于瘤胃球菌科(Ruminococcaceae)和厚壁菌门(Firmicutes)丰富度的增加[43]。De Nardi等[44]研究发现, 在荷斯坦奶牛高精料饲粮中添加100 g/d的多酚精油(主要成分为黄酮类)可以显著减少瘤胃中普雷沃氏菌和Christenenellaceae的丰富度; 此外, 由于黄酮类化合物潜在的抗菌活性, 还增加了厚壁菌门、无壁菌门(Tenericutes)和拟杆菌门(Bacteroidetes)的丰富度。

4 植物提取物对反刍动物摄食和瘤胃缓冲作用的影响

植物提取物中通常含有单宁、皂苷等抗营养物质, 可以与饲粮中淀粉相互作用并减弱其消化速率, 进而缓解高精料饲粮条件下因淀粉过快分解而造成的瘤胃pH的剧烈下降[45]; 此外, 单宁、皂苷等因可降低饲粮的适口性而减缓采食速度, 有利于降低瘤胃发酵产酸的速度。薄荷醇是薄荷精油的主要成分, 具有强烈的刺激作用。饲粮中添加薄荷精油会刺激唾液分泌, 降低泌乳奶牛饲粮的适口性, 进而增加奶牛进食时间, 可以对瘤胃pH的降低有一定的缓冲作用, 但对干物质摄入量无显著影响[46]。在内洛尔牛高精料饲粮中添加混合精油(主要成分为丁香酚、百里香酚、迷迭香等)可以显著增加反刍时间, 有利于增加瘤胃内的缓冲作用, 饲料转化效率和日增重与对照组相比也有显著提高[47]。但总体来讲, 大部分植物提取物的添加对反刍动物的采食量甚至营养物质消化率无不良影响。据Yatoo等[48]报道, 在占饲粮比例67%的精料中添加0.15 mg/kg的植物精油(主要成分为大蒜油和肉桂油)对水牛日增重有增加的趋势, 对饲粮摄入量、营养物质消化率和饲料转化效率均无显著影响。

5 小结

在反刍动物生产中, 高精料饲粮的使用会导致反刍动物瘤胃发酵异常和微生物区系紊乱, 进而发生炎症反应和一系列营养代谢疾病。饲粮中添加植物提取物可以调节瘤胃内SCFA组成、微生物区系, 降低血液中LPS浓度与炎症反应, 增加瘤胃内的缓冲作用, 缓解高精料饲粮所带来的副作用。由于植物提取物种类繁多、作用机制不尽相同, 今后尚需进一步研究植物提取物配合使用效果和适宜添加量, 以便更好地在实际生产中加以推广应用。

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