Effects of C18 Unsaturated Fatty Acids on Rumen Microbiota, Methane Emissions and Rumen Fermentation in Ruminants

WANG Yufeng; HUO Xianxian

doi:10.12418/CJAN2026.068

Chinese Journal of Animal Nutrition >

2026 , Vol. 38 >Issue 2: 866 - 878

DOI: https://doi.org/10.12418/CJAN2026.068

REVIEW

Effects of C18 Unsaturated Fatty Acids on Rumen Microbiota, Methane Emissions and Rumen Fermentation in Ruminants

WANG Yufeng ,
HUO Xianxian ^,^*

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Key Laboratory of Animal Nutrition and Feed Science at University of Inner Mongolia Autonomous Region, College of Animal Science, Inner Mongolia Agricultural University, Hohhot 010018, China

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

Received date: 2025-07-28

Online published: 2026-02-12

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Abstract

To meet the growing demand for animal products, energy-dense fat supplements are often included in ruminant diets to enhance production efficiency. Compared with saturated fatty acids (SFA), oils rich in unsaturated fatty acids (UFA) not only provide substantial energy but also have greater advantages in mitigating enteric methane emissions and improving the fatty-acid profiles of milk and meat. Among them, C18 unsaturated fatty acids (C18 UFA) are the most common and most extensively studied type in dietary oils. A substantial body of research indicates that C18 UFA can modulate the rumen microbial community and thereby alter rumen fermentation patterns. In general, dietary C18 UFA supplementation increases rumen propionate concentration, decreases acetate concentration and acetate-to-propionate ratio (A∶P), accompanied by reduced methane emissions, although responses vary among individuals and depend on dose. In addition, C18 UFA may also influence rumen pH by reducing the supply of fermentable substrates in the rumen or altering microbial activity; however, findings remain inconsistent. This review synthesizes recent studies on the effects of dietary C18 UFA supplementation on rumen microbiota, methane emissions and rumen fermentation, aiming to provide a theoretical basis for optimizing the technology of dietary oil supplementation in ruminants and promoting its efficient application in production practice.

Key words： C18 unsaturated fatty acids; ruminants; rumen microbiota; methane emissions; rumen fermentation

Cite this article

WANG Yufeng , HUO Xianxian . Effects of C18 Unsaturated Fatty Acids on Rumen Microbiota, Methane Emissions and Rumen Fermentation in Ruminants[J]. Chinese Journal of Animal Nutrition, 2026 , 38(2) : 866 -878 . DOI: 10.12418/CJAN2026.068

随着人口的持续增长与对畜产品需求的日益增加,畜牧业正逐步向规模化、集约化方向转型。为满足供给需求,生产实践中常采用高能量密度饲粮,以缩短生产周期并提高畜产品产量。油脂作为一种高能量密度的营养物质,能够在动物采食量受限条件下有效提高饲粮能量水平,从而提高生产效率^[1]。特别是在反刍动物泌乳早期^[2]、热应激^[3]或能量负平衡^[4]等特殊生理时期,适量补充油脂有助于缓解机体能量压力,维持并提高生产性能。此外,饲粮中添加油脂对于环境保护也具有重要意义。最新一项Meta分析结果显示,在7类甲烷减排策略中,油脂添加位列第4,并兼具成本较低与中等适用性的优势^[5]。值得注意的是,油脂的应用效果与其脂肪酸组成密切相关,其中饱和脂肪酸(saturated fatty acids,SFA)更适用于提高乳脂产量,不饱和脂肪酸(unsaturated fatty acids,UFA)则在降低甲烷排放和改善乳、肉产品脂肪酸组成方面更具优势^[1,6-8],且上述差异效应的产生与瘤胃微生物在发酵和代谢过程中的介导作用密不可分。在众多UFA中,以油酸(C18∶1)、亚油酸(C18∶2)和亚麻酸(C18∶3)为代表的十八碳不饱和脂肪酸(C18 UFA)是饲粮油脂中最常见且研究最广泛的类型,因此其对瘤胃发酵与微生物区系的影响具有典型性与代表性。基于此,本文综述了近年来体内、外研究中关于饲粮添加富含C18 UFA的油脂(或纯脂肪酸)对反刍动物瘤胃微生物、甲烷排放和瘤胃发酵的影响,以期为反刍动物饲粮脂肪添加技术的完善与应用提供科学依据和理论参考。

1 C18 UFA对瘤胃微生物的影响

瘤胃微生物主要包括细菌(10¹⁰~10¹¹个/mL)、古菌(10⁸~10⁹个/mL)、原生动物(10⁵~10⁶个/mL)以及真菌(10³~10⁴个/mL)4大类群^[9]。这些微生物可以通过瘤胃内3个营养级的协同作用,降解植物细胞壁中含量丰富且难降解的糖聚合物(纤维素和半纤维素),产生大量挥发性脂肪酸(volatile fatty acid,VFA),为宿主提供约70%的能量需求^[10-11],同时参与甲烷生成^[12]及代谢功能调节^[13]等过程。UFA是一类已知可通过调控瘤胃微生物群落结构及干扰生物氢化过程,进而影响瘤胃营养级效应并改变瘤胃微生态的营养物质。UFA对反刍动物饲粮营养物质消化率的影响取决于所添加UFA的类型和水平,随着UFA分子双键数和添加水平的增加,其对消化率的抑制作用也会增强^[14]。一般而言,低水平添加时,得益于瘤胃微生态系统的恢复能力和功能冗余,瘤胃整体发酵功能可维持稳定^[15],但当游离UFA总量超过一定阈值,某些微生物群落(如纤维分解菌)的活性则会被显著抑制,进而可能影响饲粮营养物质消化率^[16]。表1^[17-25]总结了部分体内、外研究中关于饲粮添加富含C18 UFA的油脂(或纯脂肪酸)对反刍动物瘤胃微生物影响的相关结果。

表1 C18 UFA对反刍动物瘤胃微生物的影响

Table 1 Effects of C18 UFA on rumen microbiota in ruminants

油脂种类 Fatty type	动物 Animal	剂量 Dose	瘤胃微生物 Rumen microbiota	参考文献 References
油酸 OA (99%)	奶牛(体外)	1.5% DM	巨球型菌属(Megasphaera)、厌氧弧菌属(Anaerovibrio)、 Lachnobacterium、假丁酸弧菌属(Pseudobutyrivibrio)相对丰度↑	[17]
菜籽油 Rapeseed oil	奶牛	5% DM	厌氧鞭菌属1(Anaeromyces 1)相对丰度↑,韦荣球菌科 (Veillonellaceae)相对丰度↓	[18]
红花油 Safflower oil			拟杆菌目S24-7(Bacteroidales S24-7)、Anaeromyces 1、Methanimicrococcus blatticola 相对丰度↑,厌氧原体科(Anaeroplasmataceae)、Methanobrevibacter gottschalkii、甲烷球形菌属ISO3 F5(Methanosphaera ISO3 F5)相对丰度↓
亚麻籽油 Linseed oil			琥珀酸弧菌科(Succinivibrionaceae)、Anaeromyces 1相对丰度↑,克里斯滕森菌科 (Christensenellaceae)、Anaeroplasmataceae、KF1相对丰度↓
玉米油 Corn oil	奶牛(体外)	3% DM	Anaerovibrio、瘤胃杆菌属(Ruminobacter)、溶淀粉琥珀酸单胞菌(Succinimonas amylolytica) 及高F∶C下瘤胃球菌属(Ruminococcus)、白色瘤胃球菌(Ruminococcus albus)相对丰度↑, 密螺旋体属(Treponema)及低F∶C下Ruminococcus、Ruminococcus albus相对丰度↓	[19]
大豆油 Soybean oil	奶牛	4% DM	栖瘤胃普雷沃氏菌(Prevotella ruminicola)、嗜淀粉瘤胃杆菌(Ruminobacter amylophilus) 数量↑,黄色瘤胃球菌(Ruminococcus flavefaciens)、Ruminococcus albus数量↓	[20]
低芥酸菜籽油 Canola oil	肉牛	5% DM	液相:普雷沃氏菌属1(Prevotella 1)、普雷沃氏菌科NK3B31群(Prevotellaceae_NK3B31_group)、解琥珀酸菌属(Succiniclasticum)、瘤胃球菌属1(Ruminococcus 1)相对丰度↑;固相:Prevotella 1、 Succiniclasticum、瘤胃球菌科NK4A214群(Ruminococcaceae_NK4A214_group)、Ruminococcus 1 相对丰度↑。液相:理研菌科RC9肠道群(Rikenellaceae_RC9_gut_group)、纤维杆菌属(Fibrobacter)、 Prevotellaceae NK3B31 group、普雷沃氏菌科UCG-003(Prevotellaceae_UCG-003)、普雷沃氏菌科 UCG-001(Prevotellaceae_UCG-001)相对丰度↓;固相:Rikenellaceae_RC9_gut_group、克里斯滕森菌科 R7群(Christensenellaceae_R-7_group)、丁酸弧菌属2(Butyrivibrio 2)、Fibrobacter相对丰度↓	[21]
菜籽精油 Canola essential oil	山羊(体外)	0.5% DM	厚壁菌门(Firmicutes)、变形菌门(Proteobacteria)、月形单胞菌属(Selenomonas)、Anaerovibrio、 Ruminococcus albus、Megasphaera spp.相对丰度↑,广古菌门(Euryarchaeota)、双歧杆菌属 (Bifidobacterium)、甲烷短杆菌属(Methanobrevibacter)、短双歧杆菌(Bifidobacterium breve)相对丰度↓	[22]
		1.0% DM	疣微菌门(Verrucomicrobia)、Anaerovibrio相对丰度↑,放线菌门(Actinobacteria)、 Methanobrevibacter、Bifidobacterium breve相对丰度↓
		1.5% DM	Firmicutes、Megasphaera spp.相对丰度↑,Bifidobacterium、乳杆菌属 (Lactobacillus)、Ruminococcus、Ruminococcus albus、Bifidobacterium breve、 Methanobrevibacter相对丰度↓
		2.0% DM	Anaerovibrio相对丰度↑,Ruminococcus、Methanobrevibacter、 Bifidobacterium breve相对丰度↓
亚麻籽油长链脂肪酸钙盐 Calcium salts of long-chain fatty acids from linseed oil	绵羊(体外)	2.25% DM	月形单胞菌属1(Selenomonas 1)、Prevotella 1、琥珀酸弧菌属(Succinivibrio)、Megasphaera、链球菌属 (Streptococcus)相对丰度↑,Rikenellaceae_RC9_gut_group、瘤胃球菌属2(Ruminococcus 2)、拟杆菌目 BS11肠道群(Bacteroidales_BS11_gut_group)、原生动物(Protozoa)相对丰度↓	[23]
		4.50% DM	Prevotella 1、Selenomonas 1、Succiniclasticum、Succinivibrio、Megasphaera、Streptococcus相对丰度↑, Rikenellaceae_RC9_gut_group、Ruminococcus 2、Bacteroidales_BS11_gut_group、 Lachnospiraceae_NK3A20_group、Methanobrevibacter、Protozoa相对丰度↓
微胶囊化共轭亚油酸粉 Microencapsulated CLA powder (80.5%)	奶山羊	90 g/d	Rikenellaceae_RC9_gut_group、Succiniclasticum、 Prevolellaceae_UCG-003、Treponema相对丰度↓	[24]
反式10,顺式12- 共轭亚油酸 t10,c12-CLA (80.0%)	初生绵羔羊	1%开食料, 饲喂5 d	拟杆菌门(Bacteroidota)、拟杆菌属(Bacteroides)、Treponema、Anaerovibrio 相对丰度↑,Firmicutes、不动杆菌属(Acinetobacter)、Succinivibrio、氨基酸球菌属 (Acidaminococcus)、Solobacterium、互营球菌属(Syntrophococcus)相对丰度↓	[25]
		1%开食料, 饲喂21 d	Bacteroidota、Bacteroides、Treponema、Anaerovibrio相对丰度↑,Firmicutes、 Acinetobacter、Succinivibrio、Acidaminococcus、Solobacterium、Syntrophococcus相对丰度↓

↑:上升 increase;↓:下降 decrease。

F∶C表示饲粮粗饲料与精饲料比例,下表同。F∶C represents the dietary forage-to-concentrate ratio. The same as below.

1.1 植物源性C18 UFA

油酸、亚油酸和α-亚麻酸均为常见的植物源性C18 UFA,已被广泛应用于反刍动物饲粮中。大量研究表明,饲粮添加C18 UFA会在不同程度上改变瘤胃微生物群落结构。部分研究观察到其对主要纤维分解菌的相对丰度无显著影响^[17-18],但更多报道指出C18 UFA的添加会导致纤维分解菌的相对丰度或数量下降^[20-23]。同时,C18 UFA的添加普遍导致瘤胃产甲烷古菌和纤毛虫数量减少,而兼性菌普雷沃氏菌属(Prevotella)和产丙酸菌[月形单胞菌属(Selenomonas)、巨球型菌属(Megasphaera)]以及脂解菌厌氧弧菌属(Anaerovibrio)的相对丰度或数量则会升高^[20-22]。已有研究证实,Selenomonas和Megasphaera数量的增加可以防止瘤胃内乳酸的积累,并增加丙酸和丁酸的生成,在预防瘤胃酸中毒方面发挥着关键作用^[26]。

C18 UFA的添加水平及饲粮组成等因素会显著影响瘤胃微生物群的响应。相较于低水平补充,添加高水平C18 UFA对瘤胃纤维分解菌、产甲烷菌和原虫活性的抑制能力更强。Idowu等^[22]在山羊的体外研究中发现,饲粮添加0.5% DM的菜籽精油(富含亚油酸)会提高瘤胃纤维分解菌白色瘤胃球菌(Ruminococcus albus)的相对丰度,但在1.5% DM和2.0% DM的添加水平下,瘤胃球菌属(Ruminococcus,包括Ruminococcus albus)的相对丰度则显著降低。Sato等^[23]在绵羊的体外试验中也发现,相比于添加2.25% DM的亚麻籽油脂肪酸钙盐,4.50% DM添加水平下更能显著降低瘤胃原虫的数量和产甲烷菌相对丰度。饲粮粗饲料与精饲料比例(F∶C)同样可调节油脂添加效果。Mitchell等^[19]的体外试验表明,玉米油添加与饲粮F∶C之间存在交互效应,在高F∶C条件下添加玉米油提高了Ruminococcus和Ruminococcus albus的相对丰度,而低F∶C条件下则呈现相反的变化。此外,不同油脂来源或脂肪酸类型对瘤胃微生物群落的影响也存在差异。Amanullah等^[27]研究发现,与补充亚油酸相比,补充α-亚麻酸(或α-亚麻酸与亚油酸1∶1混合)更显著提高了瘤胃Ruminococcus albus的数量;而与补充α-亚麻酸相比,补充亚油酸(或α-亚麻酸与亚油酸1∶1混合)则更明显地降低了产甲烷古菌的数量。其另一项试验还指出,添加玉米油组体外培养体系中Ruminococcus albus和纤毛原虫数量高于添加亚麻籽油组,而亚麻籽油组的产甲烷古菌数量则高于添加菜籽油钙盐组和添加玉米油组^[28]。

1.2 十八碳共轭脂肪酸

关于饲粮添加十八碳共轭脂肪酸对反刍动物瘤胃微生物群落的影响鲜有报道,近5年内仅发现2项与共轭亚油酸(conjugated linoleic acid,CLA)应用相关的研究。Zhang等^[24]研究发现,奶山羊饲粮中添加90 g/d微胶囊化CLA粉可显著降低瘤胃微生物ACE、Chao1和Sobs物种丰富度指数,但对代表整体多样性的Simpson和Shannon指数无明显影响;此外,CLA的添加显著降低了瘤胃理研菌科RC9肠道群(Rikenellaceae_RC9_gut_group)、解琥珀酸菌属(Succiniclasticum)和密螺旋体属(Treponema)的相对丰度。

然而,该研究存在明显局限性,尽管试验中CLA添加水平逐级递增,但微生物群分析仅对比了90 g/d CLA组与未添加组,且添加的是反式-10,顺式-12-共轭亚油酸(t10,c12-CLA)和反式-9,顺式-11-共轭亚油酸(c9,t11-CLA)的混合物,未明确单一异构体对瘤胃微生物的作用规律。Yang等^[25]研究了在断奶羔羊饲粮中添加1%的t10,c12-CLA对瘤胃微生物群落的影响,结果显示,早期断奶会提高羔羊断奶后第5天瘤胃厚壁菌门(Firmicutes)的相对丰度,并降低第5天和第21天瘤胃拟杆菌门(Bacteroidota)的相对丰度,提示微生物群落结构出现失调及潜在功能丧失;而饲粮中添加t10,c12-CLA后,断奶后第5天和第21天羔羊瘤胃中上述菌门的丰度变化与早期断奶效应相反,即t10,c12-CLA降低了Firmicutes相对丰度并提高了Bacteroidota相对丰度,表明其可能逆转早期断奶导致的瘤胃微生物群落紊乱。此外,该研究还发现t10,c12-CLA的添加显著提高了羔羊瘤胃拟杆菌属(Bacteroides)、Treponema和Anaerovibrio的相对丰度,降低了琥珀酸弧菌属(Succinivibrio)和互营球菌属(Syntrophococcus)的相对丰度。上述2项研究在试验动物、CLA添加水平以及添加类型等方面差异较大,其结果难以直接比较;且二者均仅采用16S rRNA测序技术,缺乏宏基因组学或宏转录组学等功能层面的验证,因此无法明确CLA对瘤胃微生物群落影响的具体机制。未来应围绕动物种类、CLA的异构体类型、添加水平及添加形式(游离态或瘤胃保护态)等方面展开系统研究,并结合多组学技术,更深入及准确地揭示CLA调控瘤胃微生物群功能的作用机制。

2 C18 UFA对甲烷排放的影响

C18 UFA对甲烷排放的抑制作用已被广泛证实,并在反刍动物生产中得到实际应用^[18,29]。UFA可通过直接或间接抑制产甲烷古菌与原虫的丰度以及在瘤胃生物氢化过程中作为次级“氢汇”竞争利用氢2种途径减少甲烷生成,不过后者的贡献相对较小^[7]。一项宏基因组学研究表明,UFA能够下调产甲烷菌中甲烷合成相关功能基因的表达,抑制甲烷生成途径中关键酶的活性^[6],这从分子机制层面阐释了C18 UFA抑制甲烷生成的作用机理。

C18 UFA降低甲烷排放的效果受到添加水平及饲粮组成等因素的影响。Razzaghi等^[30]研究发现,菜籽油添加水平与饲粮F∶C之间存在交互效应,无论在高粗饲料还是高精饲料饲粮中,添加菜籽油均可降低日甲烷排放量,但在高粗饲料条件下甲烷排放下降更为明显。这一现象可能归因于高粗饲料饲粮中纤维分解菌与原虫的丰度更高,其代谢过程会产生更多甲烷前体物质(如氢气和乙酸)^[31-33],而UFA对这类微生物具有较强的抑制作用^[34-35],从而表现出更显著的甲烷减排效果。C18 UFA添加水平也是影响甲烷减排效果的重要因素。在以奶牛^[36]或山羊^[37]瘤胃液为接种源的2项体外研究中均发现,添加低水平UFA对甲烷产量无显著影响,甲烷产量下降仅在高水平添加时出现。De Ondarza等^[38]的Meta分析结果进一步表明,只有在饲粮添加较高水平UFA时才会出现明显的肠道甲烷(enteric methane,eCH₄)减排效果,并且饲粮干物质中瘤胃可利用多不饱和脂肪酸(亚油酸+亚麻酸)和UFA(油酸+亚油酸+亚麻酸)总量每增加1个百分点,日eCH₄排放量分别可降低6.88%和4.65%。上述研究结果表明,富含C18 UFA的油脂对甲烷排放的抑制作用存在剂量依赖性,在反刍动物饲粮中添加高水平的C18 UFA通常能获得更显著的甲烷减排效果。

尽管不同类型C18 UFA的甲烷抑制机制相似,但其甲烷减排效果仍存在差异。一项针对绵羊的研究显示,不同C18 UFA对甲烷生成的抑制作用排序为:亚麻酸>亚油酸>油酸^[39]。Boland等^[40]在奶牛饲喂试验中也发现,与补充大豆油(富含亚油酸)相比,补充亚麻籽油(富含亚麻酸)可显著降低日甲烷排放量。总体来看,脂肪酸不饱和度越高,对甲烷生成的抑制效果越好^[14]。表2汇总了饲粮添加富含C18 UFA的油脂(或纯脂肪酸)对反刍动物体内、外甲烷排放影响的相关结果。

表2 C18 UFA对反刍动物甲烷排放的影响

Table 2 Effects of C18 UFA on methane emissions in ruminants

油脂种类 Fatty type	动物 Animal	剂量 Dose	甲烷排放 Methane emissions	参考文献 References
菜籽油Rapeseed oil	奶牛	5% DM	显著降低了瘤胃中甲烷总排放量(g/d)和单位产奶甲烷排放强度(g/kg ECM);添加红花籽油或亚麻籽油进一步降低了甲烷能损占总能比例(%)	[18]
红花油Safflower oil
亚麻籽油Linseed oil
菜籽油Rapeseed oil	奶牛	5% DM	甲烷总排放量(g/d)受饲粮F∶C和油脂添加交互效应影响,高粗饲料条件下甲烷排放下降更为明显;在高、低F∶C条件下,菜籽油的添加都会降低单位干物质采食量甲烷产量(g/kg DMI)及单位产奶甲烷排放强度(g/kg ECM)	[30]
菜籽油Rapeseed oil	奶牛(体外)	4% DM、 8% DM	添加菜籽油或4% DM亚麻籽油对甲烷日排放量 (mmol/d)无显著影响,添加8% DM亚麻籽油导致甲烷日排放量(mmol/d)显著下降	[36]
亚麻籽油Linseed oil		4% DM、 8% DM
大豆油Soybean oil	奶牛	精饲料中额外添加 720 g/d 膳食脂肪	相比于添加大豆油,添加亚麻籽油后甲烷总排放量 (g/d),单位产奶甲烷产量(g CH₄/kg milk),单位干物质采食量甲烷产量(g CH₄/kg DMI),单位添加脂肪酸甲烷产量(g CH₄/g of added FA),甲烷能损占总能比例(%)均显著下降	[40]
亚麻籽油Linseed oil
橄榄油Olive oil	绵羊(体外)	6% DM	显著降低了发酵罐内总产气中甲烷体积分数 (mL/dL)、每日甲烷产量(mL/d)和单位可发酵有机质甲烷产率(mmol/g fermentable OM)	[29]
葵花籽油Sunflower oil
亚麻籽油Linseed oil
石榴籽油 Pomegranate seed oil	山羊(体外)	在塑料注射器中分别添加5或10 mg 油脂	随着石榴籽油添加量的增加,单位干物质甲烷产量(mL/g DM)呈下降趋势;当添加量达到10 mg时,单位干物质甲烷产量 (mL/g DM)较对照组出现显著降低	[37]

3 C18 UFA对瘤胃发酵的影响

3.1 pH

瘤胃pH不仅会影响VFA的吸收速率^[41],也是反映瘤胃微生物活性、发酵过程及反刍动物整体健康状况的重要指标^[42]。关于饲粮添加UFA对瘤胃pH的影响,现有研究结论尚不一致。多数研究支持以下假设:UFA通过抑制瘤胃纤维降解菌的活性^[14],减少总可发酵底物,从而降低瘤胃总挥发性脂肪酸(total volatile fatty acid,TVFA)浓度,并导致pH升高^[10]。例如,在奶牛^[43]或绵羊^[44]饲粮中添加C18 UFA后,观察到瘤胃TVFA浓度显著下降,同时pH上升。Xin等^[45]对146篇文献进行的Meta分析也证实了这一结论,即饲粮添加C18 UFA可降低牛瘤胃TVFA浓度并提高pH。与之相反,另有部分研究报道饲粮添加C18 UFA可提高瘤胃TVFA浓度并降低pH^[46-48]。值得注意的是,并非所有研究中瘤胃pH的变化都伴随着TVFA浓度的显著改变。例如,Bahramkhani-Zaringoli等^[49]在羔羊饲粮中添加大豆油后发现,瘤胃TVFA浓度无明显变化,但pH却显著升高,这提示C18 UFA可能通过非VFA依赖的其他途径调控瘤胃pH。亚急性瘤胃酸中毒(subacute ruminal acidosis,SARA)的判定标准为瘤胃pH每天至少持续3 h处于5.2~5.8^[50]。在现有报道中,仅个别研究(如一项饲粮添加大豆油和亚麻籽油的研究^[47])观察到C18 UFA的添加导致瘤胃pH降至SARA阈值范围。更多研究显示C18 UFA的添加可使瘤胃pH升高,这提示饲粮添加C18 UFA可能有助于在高精料饲粮喂养的早期阶段稳定瘤胃pH,其潜在机制可能与C18 UFA延缓瘤胃发酵进程有关^[51]。不过,当前支持这一推测的证据较为有限,还需进一步通过试验验证。

C18 UFA的类型、来源及添加水平均会影响其对瘤胃pH的作用。Amanullah等^[28]研究发现,与饲喂添加玉米油的饲粮相比,饲喂添加菜籽油钙盐饲粮的育肥牛,其瘤胃pH显著升高;而饲喂添加亚麻籽油饲粮的育肥牛瘤胃pH介于前两者之间。即使补充相同类型的C18 UFA,不同油脂来源对瘤胃pH的影响也可能存在差异。Signor等^[52]在奶牛饲粮中添加不同来源的亚油酸后发现,与添加大豆油相比,饲粮中添加葡萄籽油使产后第15天瘤胃pH显著升高。此外,Lima等^[53]报道,在绵羊羔饲粮中添加大豆油后,瘤胃pH随油脂添加水平的提高呈现二次变化趋势:当添加水平为6% DM时,瘤胃pH达到峰值;当添加水平增至12% DM时,pH降至最低。

3.2 VFA

饲粮添加C18 UFA对反刍动物VFA的影响已有大量研究报道,但研究结果之间存在较大差异。部分研究表明,饲粮添加C18 UFA对瘤胃TVFA浓度及各VFA比例未产生显著影响^[54-55],然而也有研究观察到TVFA浓度及VFA组成发生了显著改变^[17,25,47]。一项Meta分析指出,饲粮添加C18 UFA油脂补充剂可显著提高瘤胃丙酸浓度,同时降低TVFA、乙酸浓度及乙丙比(A∶P)^[45],在2项针对肉牛的菜籽油饲喂试验^[56-57]中也观察到了相似的结果。上述研究中观察到的丙酸浓度增加可能是由于C18 UFA刺激了丙酸生成菌(如Selenomonas、Megasphaera)及脂解菌Anaerovibrio相对丰度的增加,其中Anaerovibrio可将油脂水解为脂肪酸和甘油,而甘油是丙酸生成的重要前体^[58-59]。此外,C18 UFA对产甲烷菌的抑制作用,使得瘤胃中的氢更多地流向丙酸合成途径^[60],这可能也是导致丙酸浓度增加的重要因素。丙酸作为反刍动物瘤胃中利用率最高的VFA,是其中唯一可直接进入肝脏糖异生途径的底物,可为反刍动物提供60%~74%的糖异生碳源^[61-62]。同时,丙酸合成过程中对氢离子的竞争性利用,可进一步抑制甲烷生成,从而提高饲粮能量转化效率及减少温室气体排放^[60]。而乙酸作为乳脂合成的首要底物^[63],其浓度下降也部分解释了多数研究中观察到的“饲粮添加C18 UFA后乳脂合成量及乳脂率降低”这一现象^[47,64-65]。然而,也有研究发现饲粮添加C18 UFA会使瘤胃发酵模式向乙酸型发酵转变。例如Nur Atikah等^[66]和Zhang等^[48]的研究均指出,饲粮添加C18 UFA会导致山羊瘤胃TVFA浓度、乙酸比例或A∶P升高,而丙酸比例则保持不变或有所下降。由此可见,C18 UFA对瘤胃VFA产量以及组成的影响并非单一效应,还存在其他因素影响C18 UFA对瘤胃发酵功能的作用效果。

大量研究指出,随着饲粮C18 UFA添加水平的提高,瘤胃内某些VFA浓度及比例会呈现线性或二次变化趋势。Arcos-Álvarez等^[67]研究发现,羔羊饲粮中添加橄榄油后,瘤胃丙酸比例呈二次下降趋势,在4% DM添加水平时最高;而丁酸比例则呈二次上升趋势,并在4% DM添加水平时降至最低。C18 UFA的类型不同,其对瘤胃VFA的调控效应也存在差异。Kholif等^[47]将亚麻籽油、大豆油及二者1∶1混合油脂分别添加至山羊饲粮中,结果显示,亚麻籽油饲粮组山羊瘤胃丙酸比例显著高于大豆油与混合油脂饲粮组;而大豆油饲粮组山羊瘤胃丁酸比例则显著高于亚麻油饲粮组。此外,即便C18 UFA类型一致,不同油脂来源也会导致其对瘤胃VFA的影响效果不尽相同。Signor等^[52]在奶牛饲粮中分别添加富含亚油酸的葡萄籽油或大豆油,结果发现与大豆油组相比,葡萄籽油组奶牛在产后第15天的瘤胃丙酸浓度更高,而TVFA、乙酸浓度及A∶P则更低。有研究还探讨了不同F∶C条件下添加C18 UFA对瘤胃VFA的影响,发现随着饲粮粗饲料比例的提高,瘤胃内丙酸比例呈线性降低,而乙酸比例呈线性上升^[68]。但该研究未进一步探究F∶C与油脂添加之间是否存在交互效应,因此无法明确瘤胃VFA的变化是由饲粮F∶C或油脂添加单独作用,还是二者共同作用的结果。Mitchell等^[19]则通过在不同F∶C的奶牛饲粮中添加玉米油,证实饲粮F∶C与油脂添加对瘤胃VFA的影响不存在交互效应。值得注意的是,Mirzaei-Alamouti等^[69]发现饲喂频次也会影响C18 UFA在奶牛饲粮中的应用效果,且二者存在显著交互效应。该研究在奶牛饲粮中添加富含亚油酸的黄油后发现,每天饲喂3次时,瘤胃乙酸比例与A∶P均无显著变化;而每天饲喂1次时,乙酸比例与A∶P则显著升高。与之相对应,丙酸比例在每天饲喂3次时未发生显著改变,但在每天饲喂1次时显著降低。表3总结了体内、外研究中饲粮添加富含C18 UFA的油脂(或纯脂肪酸)对反刍动物瘤胃pH、VFA浓度与组成的影响。

表3 C18 UFA对反刍动物瘤胃pH、VFA浓度与组成的影响

Table 3 Effects of C18 UFA on rumen pH, VFA concentration and composition in ruminants

油脂种类 Fatty type	动物 Animal	剂量 Dose	瘤胃pH、VFA浓度与组成 Rumen pH, VFA concentration and composition	参考文献 References
油酸OA (99%)	奶牛(体外)	1.5% DM	丙酸和总挥发性脂肪酸(TVFA)浓度显著降低	[17]
葡萄籽油Grapeseed oil	奶牛	25 mL/d	与大豆油相比,饲喂添加葡萄籽油饲粮的奶牛瘤胃TVFA、乙酸浓度和pH在产后第15天显著降低	[52]
大豆油Soybean oil
葵花籽油Sunflower oil	奶牛	3% DM	添加油脂后,随着饲粮粗饲料比例增加,瘤胃乙酸比例、乙丙比(A∶P)线性上升,丙酸比例线性下降	[68]
亚麻籽油Linseed oil	奶牛	2% DM、3% DM、4% DM	TVFA浓度、乙酸比例和A∶P线性下降,丙酸比例线性上升;pH呈线性或先降后增的二次变化,4% DM添加水平时最高;丁酸比例呈先增后降的二次变化,3% DM添加水平时最高	[43]
黄油Butter	奶牛	2.5% DM	乙酸、丙酸比例和A∶P受饲喂频次和油脂添加交互效应的影响。乙酸比例和A∶P在每天饲喂 3次时无显著变化,每天饲喂1次时显著降低; 丙酸比例在每天饲喂3次时无显著变化,但在每天饲喂1次时显著降低	[69]
低芥酸菜籽油Canola oil	肉牛	5% DM	乙酸、丙酸比例和A∶P受到3-硝基氧丙醇(3-NOP) 和油脂添加交互效应的影响。在有3-NOP时,添加油脂后乙酸比例和A∶P下降,丙酸比例不变;在无3-NOP时,添加油脂后乙酸比例和A∶P不变, 丙酸比例上升。pH不受交互效应的影响,并在处理前后无显著差异	[57]
低芥酸菜籽油Canola oil	肉牛	5% DM	pH和丙酸比例受硝酸盐与油脂添加的交互效应影响。无论饲粮中是否添加硝酸盐,补充油脂对pH均无显著影响。然而,在未添加硝酸盐时, 补充油脂会提高丙酸比例;而在添加硝酸盐的情况下,补充油脂反而使丙酸比例下降	[56]
玉米油Corn oil	肉牛(体外)	4.7% DM	体外培养24 h后菜籽油钙盐组pH、乙酸比例和 A∶P最高,玉米油组丙酸比例最高	[28]
亚麻籽油Linseed oil
菜籽油钙盐 Calcium salts of rapeseed oil
低芥酸菜籽油Canola oil	山羊	3% DM	大豆油显著提高了pH(从5.98上升至6.34), 油脂添加对VFA浓度无显著影响	[54]
葵花籽油Sunflower oil
大豆油Soybean oil
橄榄油Olive oil	山羊	6% DM	TVFA浓度和乙酸比例显著提高, 对pH无显著影响	[66]
葵花籽油Sunflower oil
玉米油Corn oil	山羊	3% DM	TVFA浓度和乙酸比例显著提高, 丙酸比例和pH显著降低	[48]
亚麻籽油Flaxseed oil	山羊	20 mL/d	pH、乙酸比例和A∶P显著降低,TVFA 浓度和丙酸比例显著提高	[46]
橄榄油Olive oil	绵羊羔	2% DM、 4% DM、 6% DM	pH和丁酸比例呈先降后增的二次变化, 6% DM添加时最高;丙酸比例呈先增后降的二次变化,4%添加时最高	[67]
大豆油Soybean oil	绵羊羔	3% DM、 6% DM、 9% DM、 12% DM	随添加水平提高,pH呈趋于显著的先增后降的二次变化;对VFA浓度及组成比例无显著影响	[53]
大豆油Soybean oil	绵羊羔	5% DM	乙酸比例显著降低,丙酸比例和pH显著提高	[49]

4 小结

饲粮中添加C18 UFA能够重塑瘤胃微生物群落结构,表现为部分纤维分解菌、产甲烷菌和原虫的活性与丰度下降,同时部分次级发酵菌群的相对丰度或数量上升。这种微生物群落的变化促使瘤胃发酵模式向丙酸型发酵转变,并伴随着甲烷排放量的降低,进而提升饲粮能量利用效率,减少环境污染。然而,C18 UFA的调控效果易受脂肪酸类型、添加水平、动物品种、年龄、生理阶段及饲粮组成等多种因素影响。因此,在生产实践中应用富含C18 UFA的油脂(或纯脂肪酸)时,需综合考量上述因素,以期获得最佳的动物生产效益和环境效益。

References

Publishing order | Descend order by publishing year | Descend order by cited within

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[69]

MIRZAEI-ALAMOUTI

, AKBARI-PABANDI

, MANSOURYAR

, et al. Effects of feeding frequency and oil supplementation on feeding behavior,ruminal fermentation,digestibility,blood metabolites,and milk performance in late-lactation cows fed a high-forage diet[J]. Journal of Dairy Science, 2020, 103(12):11424-11438.

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