Chinese Journal of Animal Nutrition >

2023 , Vol. 35 >Issue 6: 3745 - 3753

DOI: https://doi.org/10.12418/CJAN2023.347

RESEARCH PAPER

Effect of Medium-Chain Glyceride Complex on Performance, Serum Biochemical Indexes, Intestinal Microflora of Layers in Later Stage

  • ZHANG Hongyan , 1 ,
  • CHEN Junlie 2 ,
  • YANG Runhua 1 ,
  • HUANG Yuliang 3 ,
  • GE Hui 3 ,
  • GAO Fengxian , 1, *
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  • 1 College of Animal Science and Technology, Hunan Agricultural University, Changsha 410000, China
  • 2 Hunan Xiangjia Animal Husbandry Co., Ltd., Changde 415000, China
  • 3 Intech(Changsha)Bio-Chem Co., Ltd., Changsha 410000, China
*professor, E-mail:

Received date: 2022-11-30

  Online published: 2023-06-08

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Abstract

The objective of this experiment was the effects of medium-chain glyceride (MCG) complex on performance, serum biochemical indexes, intestinal morphology and microflora of layers in later stage. In this trail, a total of 384 Lohmann-pink layers at 492 days of age were selected and randomly divided into 4 groups with 6 replicates in each group, 16 hens in each replicate. The control group was fed a basal diet, and the other three experimental groups were added 1, 2 and 3 g/kg MCG complex in the basal diet, respectively.The test period was 60 days. Results showed as follows: 1) compared with the control group, average feed intake and egg production rate of layers in experimental groups were significantly improved (P<0.05); the dirty egg rate of layers in 1 and 2 g/kg groups was dramatically reduced (P<0.05). 2) Compared with the control group, the contents of serum total cholesterol, triglyceride and urea of layers in experimental groups were significantly reduced (P<0.05); the activities of serum glutamic oxaloacetic transaminase and glutamic alanine transaminase of layers in 3 g/kg group were dramatically reduced (P<0.05), and the activity of serum alkaline phosphatase in 1 and 2 g/kg groups was dramatically reduced (P<0.05). 3) Compared with the control group, the villus height and the ratio of villus to crypt in duodenum of layers in experimental group were significantly increased (P<0.05), while crypt depth was significantly decreased (P<0.05); the crypt depth in jejunum of layers in 1 and 2 g/kg groups was dramatically decreased (P<0.05); and different levels of MCG complex significantly increased the velvet crypt ratio in jejunum (P<0.05). 4) Compared with the control group, the number of E. coli in the duodenum in 3 g/kg group was significantly decreased (P<0.05), and the number of E. coli in the jejunum and cecum in 2 g/kg group was significantly decreased (P<0.05); the number of Salmonella in 2 and 3 g/kg groups was significantly decreased (P<0.05), and the number of Salmonella in 1 g/kg group was significantly decreased (P<0.05). In summary, the addition of MCG complex to the diet can improve the later performance of layers, improve serum biochemical indexes and optimize the structure of intestinal morphology and microflora of layers, and the optimum dose is 1 g/kg.

Key words： medium-chain glycerides; lactic acid bacteria; layers; performance; serum biochemical indexes; intestinal morphology; intestinal microflora

Cite this article

ZHANG Hongyan , CHEN Junlie , YANG Runhua , HUANG Yuliang , GE Hui , GAO Fengxian . Effect of Medium-Chain Glyceride Complex on Performance, Serum Biochemical Indexes, Intestinal Microflora of Layers in Later Stage[J]. Chinese Journal of Animal Nutrition, 2023 , 35(6) : 3745 -3753 . DOI: 10.12418/CJAN2023.347

中链甘油酯复合物成分为中链甘油酯(medium-chain glyceride,MCG)和乳酸菌(lactic acid bacteria,LAB)。中链脂肪酸(medium chain fatty acid,MCFA)是含有6~12个碳原子链的饱和脂肪酸,包括辛酸(C8)、葵酸(C10)和月桂酸(C12)。MCG在自然界中多存在于椰子油、乳脂和棕榈仁油内,但含量较少,其主要来源是通过人工将MCFA与甘油进行酯化提纯获得[1]。MCG相较于MCFA可更好地规避适口性、腐蚀性、氧化性等问题;且其分子质量小、能量高,可被机体迅速吸收代谢,被当作功能性或营养性保健油用于各种食品和药物配方中[2]。因其高能、易吸收等特性,也被广泛用于畜禽饲养中,是一种很好的饲料添加剂。LAB可利用葡萄糖等可发酵碳水产生许多乳酸,其作为益生菌家族中重要一员,广泛存在于畜禽肠道中,是肠道天然微生物群一部分,对维持机体稳态、促进宿主身体健康具有积极作用[3-4]。前人研究发现,饲粮中添加特定量MCG有助于增加蛋鸡生产性能、改善血液指标和肠道形态、优化肠道菌群结构[5]。也有学者指出,在畜禽饲粮中添加适量ALB可减少有害菌群在畜禽肠道定植从而提高其生产性能,还可降低蛋鸡血清胆固醇含量,提高免疫应答水平,减轻其应激反应[6-7]。由此可见,MCG和LAB在畜禽生产中均可起到有利作用,都在一定程度上提高了畜禽生产力、改善血清生化指标、促进畜禽肠道健康。二者作为畜禽饲料添加剂前人皆有研究,但MCG在蛋鸡上的研究较少,二者联合使用更鲜见报道。因此,本试验旨在探究MCG复合物对蛋鸡后期生产性能、血清生化指标、肠道形态和菌群的影响,以期为蛋鸡科学养殖和生产提供参考。

1 材料与方法

1.1 试验材料

试验鸡为湖南湘佳牧业股份有限公司提供的492日龄罗曼粉蛋鸡,共384只。MCG复合物为白色粉末状,来自某(长沙)生物科技有限公司,主要成分为:MCG(主要为中链甘油三酯,少量为中链甘油二酯和单甘油酯)≥30%,乳酸菌(主要为嗜酸乳杆菌)≥2×107 CFU/g。

1.2 试验设计

选取健康、产蛋率相近的492日龄蛋鸡384只,随机分为4个组,每组6个重复,每个重复16只。4组蛋鸡分别饲喂基础饲粮(对照组)、基础饲粮+1 g/kg MCG复合物、基础饲粮+2 g/kg MCG复合物、基础饲粮+3 g/kg MCG复合物。预试期3 d,正试期为60 d。参与试验的所有蛋鸡均在同一栋鸡舍,环境、光照、饮水一致,采用阶梯式笼养,饲养密度为每笼8只,每日07:00、10:00、13:00、16:00、19:00进行人工喂料,饮水自由,消毒免疫时间、方法与鸡场同步。基础饲粮为玉米-豆粕型饲粮,其组成及营养水平见表1。
表1 基础饲粮组成及营养水平(风干基础)

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

项目 Items 含量 Content
原料 Ingredients
玉米 Corn 40.00
豆粕 Soybean meal 20.30
玉米蛋白粉 Corn gluten meal 2.00
菜籽粕 Rapeseed meal 2.00
麦麸 Wheat bran 2.20
石粉 Limestone 2.50
石粒 Stone grain 2.30
食盐 NaCl 0.30
混合油 Mixed oil 0.60
碳酸氢钙 Ca(HCO3)2 1.40
糙玉混合物 Coarse corn blend 20.00
益康粉 Yikang powder 1.00
预混料 Premix1) 1.50
合计 Total 100.00
营养水平 Nutrient levels2)
代谢能 DE/(MJ/kg) 11.04
粗蛋白质 CP 16.46
粗纤维 CF 3.14
钙 Ca 3.70
总磷 TP 0.64
赖氨酸 Lys 0.75
蛋氨酸 Met 0.45
苏氨酸 Thr 0.61

1)预混料为每千克饲粮提供 The premix provided the following per kg of the diet:VA 8 500 IU,VD 3 000 IU,VE 25 IU,VB 1 125 μg,VK 2.4 mg,Mn 90 mg,Zn 70 mg,Fe 20 mg,Cu 10 mg,Co 0.1 mg,Se 0.3 mg,碘化钾 KI 0.5 mg。

2)除代谢能以外,其余值均为实测值。Except for ME, other values were measured values.

1.3 测定指标与方法

1.3.1 生产性能测定

试验期以重复为单位精确记录蛋鸡每天的喂料量、剩料量、日产蛋量、蛋重、破蛋数、脏蛋数(蛋壳上有肉眼可见的粪便、污斑、血色等脏物)。根据初步记录的数据,计算各组的平均采食量(ADFI)、产蛋率、破蛋率、蛋重、料蛋比、脏蛋率。

1.3.2 血清生化指标测定

试验结束时,从每组每个重复选取1只鸡,共24只。用翅根静脉取血法每只抽取5 mL左右血液,血液静至30 min,放入离心机3 000 r/min离心10 min,取上清液1.0~1.5 mL放入离心管,做好标记,置于-20 ℃冰箱保存,用于检测血清总胆固醇(total cholesterol,TC)、甘油三脂(triglyceride,TG)、低密度脂蛋白(low density lipoprotein,LDL)、高密度脂蛋白(high density lipoprotein,HDL)、尿素(carbamide,UREA)、尿酸(uric acid,UA)含量及谷草转氨酶(aspartate transaminase,AST)、谷丙转氨酶(alanine aminotransferase,ALT)、碱性磷酸酶(alkaline phosphatase,ALP)活性。试剂盒均采购于北京华英生物技术研究所,具体操作见说明书。

1.3.3 肠道形态测定

将采集过血液的鸡进行屠宰解剖,分别取小肠各部位1 cm左右的肠段,置于4%多聚甲醛固定液中固定1 d以上,而后制作切片,通过明美显微数码测量分析系统测量绒毛高度(villus height,VH)、隐窝深度(crypt depth,CD),并计算绒隐比(VH/CD)。

1.3.4 肠道菌群的测定

解剖后的蛋鸡,取其小肠、盲肠部位内容物,而后迅速放入液氮罐内保存,最后放入-80 ℃冰箱内,用以检测小肠、盲肠沙门氏菌、大肠杆菌数量。检测方法用平板计数法。

1.4 数据处理与分析

使用Excel 2016软件进行试验数据整理,使用SPSS 26.0软件分析数据,肠道菌群指标采用Kruskal-Wallis H检验,结果以中位数(P25,P75)形式呈现;采用单因素方差分析进行差异性比较,差异显著采用Duncan氏法进行多重比较,结果以“平均值±标准差”呈现,P<0.05表示显著差异。

2 结果与分析

2.1 MCG复合物对蛋鸡后期生产性能的影响

由表2可见,与对照组相比,不同水平MCG复合物均能显著增加蛋鸡平均日采食量和产蛋率(P<0.05);添加1和2 g/kg MCG复合物可显著降低蛋鸡脏蛋率(P<0.05);但添加不同水平MCG复合物对蛋鸡料蛋比、蛋重、破蛋率均无显著影响(P>0.05)。
表2 MCG复合物对蛋鸡后期生产性能的影响

Table 2 Effects of MCG complex on performance of layers in later stage

项目
Items		 组别 Groups P值
P-value
对照 Control 1 g/kg 2 g/kg 3 g/kg
平均日采食量 ADFI/g 117.86±3.15a 121.82±2.76b 120.79±1.74b 122.61±1.53b 0.014
产蛋率 Laying rate/% 88.96±2.10a 94.86±3.37b 92.27±1.30b 92.48±3.12b 0.008
料蛋比 F/G 2.06±0.04 1.99±0.10 2.04±0.04 2.07±0.05 0.158
蛋重 Egg weight/g 64.33±1.05 64.58±1.23 64.24±0.50 64.05±1.07 0.827
破蛋率 Broken egg rate/% 0.60±0.47 0.42±0.37 0.22±0.16 0.48±0.27 0.308
脏蛋率 Dirty egg rate/% 1.50±0.59a 0.66±0.32b 0.69±0.42b 1.22±0.73ab 0.036

同行数据肩标无字母或相同字母表示差异不显著(P>0.05),不同字母表示差异显著(P<0.05)。表3、表4同。

In the same row, values with no letter or the same letter superscripts mean no significant difference (P>0.05), while with different letter superscripts mean significant difference (P<0.05).The same as Table 3 and Table 4.

2.2 MCG复合物对蛋鸡后期血清生化指标的影响

由表3可见,与对照组相比,添加不同水平MCG复合物均能显著降低蛋鸡血清中TC、TG和UREA的含量(P<0.05);添加3 g/kg的MCG复合物可显著降低蛋鸡血清AST和ALT的活性(P<0.05);添加1和2 g/kg的MCG复合物可显著降低蛋鸡血清中ALP的活性(P<0.05);但添加不同水平MCG复合物对蛋鸡血清中HDL、LDL和UA的含量无显著影响(P>0.05)。
表3 MCG复合物对蛋鸡后期血清生化指标的影响

Table 3 Effects of MCG complex on serum biochemical indexes of layers in later stage

项目
Items		 组别 Groups P值
P-value
对照 Control 1 g/kg 2 g/kg 3 g/kg
总胆固醇 TC/(mmol/L) 5.28±0.61a 3.82±0.72b 4.13±0.55b 3.46±1.03b 0.017
甘油三酯 TG/(mmol/L) 37.88±4.63a 29.12±4.47b 29.49±3.13b 23.95±7.19b 0.009
高密度脂蛋白 HDL/(mmol/L) 1.47±0.26 1.24±0.21 1.76±0.79 1.36±0.42 0.387
低密度脂蛋白 LDL/(mmol/L) 1.26±0.15 1.02±0.10 1.08±0.15 1.05±0.38 0.322
尿素 UREA/(mmol/L) 0.67±0.16a 0.33±0.21b 0.34±0.18b 0.31±0.12b 0.029
尿酸 UA/(μmol/L) 158.35±14.05 135.19±40.43 149.69±28.74 136.21±26.60 0.650
谷草转氨酶 AST/(U/L) 171.00±7.36a 165.54±6.06a 174.77±3.74a 141.90±18.48b 0.007
谷丙转氨酶 ALT/(U/L) 176.83±26.24a 117.37±10.07ab 154.42±28.84ab 94.54±50.06b 0.024
碱性磷酸酶 ALP/(U/L) 378.92±98.38a 199.80±52.52b 219.86±34.91b 311.17±61.99ab 0.029

2.3 MCG复合物对蛋鸡后期肠道形态的影响

由表4可见,与对照组相比,添加不同水平MCG复合物均可显著提高蛋鸡十二指肠VH和VH/CD(P<0.05),显著降低CD(P<0.05);添加1、2 g/kg MCG复合物可显著降低蛋鸡空肠CD(P<0.05);添加不同水平MCG复合物均可显著提高蛋鸡空肠VH/CD(P<0.05);添加不同水平MCG复合物对蛋鸡空肠VH、回肠VH、CD与VH/CD皆影响不显著(P>0.05)。
表4 MCG复合物对蛋鸡后期肠道形态的影响

Table 4 Effects of MCG complex on intestinal morphology of layers in later stage

项目
Items		 组别 Groups P值
P-value
对照 Control 1 g/kg 2 g/kg 3 g/kg
十二指肠 Duodenum
绒毛高度 VH/μm 1 207.36±148.08a 1 530.07±144.54b 1 499.11±274.32b 1 443.85±141.92b 0.028
隐窝深度 CD/μm 95.55±7.09a 56.01±5.13c 64.73±11.45bc 70.18±7.15b <0.001
绒隐比 VH/CD 12.70±1.79a 27.51±3.61c 23.28±2.50b 20.62±5.98b <0.001
空肠 Jejunum
绒毛高度 VH/μm 1 158.00±168.99 1 257.26±187.12 1 325.08±169.41 1 242.76±271.17 0.573
隐窝深度 CD/μm 83.36±11.18a 67.95±6.42b 63.60±6.54b 72.85±9.98ab 0.006
绒隐比 VH/CD 13.97±1.95a 18.46±1.59bc 20.89±2.28c 16.94±2.38b <0.001
回肠 Ileum
绒毛高度 VH/μm 896.26±156.47 987.78±48.64 913.70±261.24 867.72±189.14 0.886
隐窝深度 CD/μm 61.87±9.95 59.16±7.91 58.21±7.53 49.15±9.39 0.213
绒隐比 VH/CD 14.70±2.79 16.96±2.95 15.47±2.65 17.73±3.91 0.448

2.4 MCG复合物对蛋鸡后期肠道菌群的影响

由表5可见,各组间十二指肠大肠杆菌数量存在统计学差异(H=10.210,P=0.029),组间比较可知,3 g/kg组与对照组存在统计学差异(P<0.05)。各组间空肠大肠杆菌数量存在统计学差异(H=10.745,P=0.013),组间比较可知,2 g/kg组与对照组存在统计学差异(P<0.05)。各组间盲肠大肠杆菌数量存在统计学差异(H=11.835,P=0.008),组间比较可知,2 g/kg组与对照组存在统计学差异(P<0.05)。回肠组(H=7.400,P=0.060)各组间菌群数量无统计学差异(P>0.05)。
各组间十二指肠沙门氏菌数量存在统计学差异(H=10.057,P=0.018),组间比较可知,2和3 g/kg组与对照组存在统计学差异(P<0.05)。各组间回肠沙门氏菌数量存在统计学差异(H=10.492,P=0.015),组间比较可知,1和3 g/kg组与对照组存在统计学差异(P<0.05)。空肠(H=5.612,P=0.132)、盲肠(H=5.565,P=0.135)各组间菌群数量均无统计学差异(P>0.05)。
表5 MCG复合物对蛋鸡后期肠道菌群的影响

Table 5 Effects of MCG complex on intestinal microflora of layers in later stage

项目
Items		 组别 Groups H值
H-value		 P值
P-value
对照 Control 1 g/kg 2 g/kg 3 g/kg
大肠杆菌 Escherichia coli/(CFU/mL)
十二指肠
Duodenum		 2.05×109
(1.43×109,2.83×109)		 1.20×103
(0,6.75×108)		 0
(0,9.00×108)		 0
(0,0)A		 10.210 0.029
空肠
Jejunum		 1.80×109
(7.37×105,2.50×109)		 0
(0,1.42×107)		 0
(0,2.43×106)A		 2.35×102
(0,8.26×104)		 10.745 0.013
回肠
Ileum		 1.70×109
(2.68×106,2.20×109)		 3.70×103
(0,2.30×109)		 1.00×103
(0,4.95×106)		 3.50×102
(0,1.63×107)		 7.400 0.060
盲肠
Cecum		 4.10×105
(1.24×105,2.85×106)		 2.90×104
(2.25×102,3.33×105)		 0
(0,1.89×104)A		 1.30×104
(0,7.68×104)		 11.835 0.008
沙门氏菌 Salmonella/(CFU/mL)
十二指肠
Duodenum		 1.18×109
(0,1.83×109)		 0
(0,6.25×104)		 0
(0,0)A		 0
(0,0)A		 10.057 0.018
空肠
Jejunum		 1.30×108
(0,6.50×108)		 0
(0,2.62×106)		 1.85×102
(0,8.78×104)		 0
(0,0)		 5.612 0.132
回肠
Ileum		 2.90×108
(3.75×105,5.83×108)		 0
(0,2.50×104)A		 1.45×104
(0,7.53×106)		 0
(0,4.75×104)A		 10.492 0.015
盲肠
Cecum		 3.20×103
(0,2.58×105)		 0
(0,1.45×103)		 0
(0,55)		 0
(0,0)		 5.565 0.135

同行数据肩标A表示与对照组比差异显著(P<0.05)。

Peer data shoulder code A indicates different difference compared with control group (P<0.05).

3 讨论

3.1 MCG复合物对蛋鸡后期生产性能的影响

MCG在动物生长发育过程中起着重要作用,可有效提高动物对营养物质的吸收和脂质代谢,从而促进其生长发育[8]。Liu等[9]在蛋鸡基础饲粮中添加不同水平MCG(150和300 mg/kg)发现,MCG可通过刺激与产蛋相关性激素的分泌、提高血清钙和脂质代谢水平、增加饲料利用率、调节肠道菌群结构,从而提高蛋鸡产蛋率。Liu等[10]在蛋鸡饲粮中添加300 mg/kg MCG发现,MCG可调节蛋鸡肠道菌群微生物结构,显著提高饲料转化率和产蛋率。LAB多存在于动物肠道中,其可增加食物消化率,降低机体胆固醇水平,具有调节肠道菌群平衡、参与免疫反应、抑制肠道致病菌的生长繁殖等多种益生功能[11]。Saleh等[12]在蛋鸡基础饲粮中添加0.1% LAB发现,LAB可提升蛋鸡采食量、增加产蛋率、降低料蛋比。本试验结果表明,不同水平MCG复合物组蛋鸡平均采食量和产蛋率显著提高,这与上述研究结果相似,表明MCG复合物可改善蛋鸡生产性能。结合Liu等[9]和崔磊等[11]的研究结果推测MCG复合物发挥作用的原理为:MCG刺激了蛋鸡体内与产蛋相关性激素的分泌,提高了钙等矿物质的代谢水平,LAB又可抑制肠道病原微生物的繁殖,改善肠道菌群环境,两者相互作用,从而促进了肠道的消化吸收能力,提高了蛋鸡的生产性能。本试验1和2 g/kg组蛋鸡脏蛋率显著降低,这项指标前人鲜有研究,推测其可降低脏蛋率原因是MCG复合物调节了蛋鸡肠道菌群结构,从而优化蛋鸡产蛋环境,使得蛋体更加清洁。本试验各组间料蛋比差异均不显著,这与Liu等[10]和Saleh等[12]研究结果有所不同,可能是本试验MCG复合物在提高蛋鸡采食量的同时增加了其产蛋率,从而导致其总体蛋重亦增加,进而使各组间料蛋比无显著差异。

3.2 MCG复合物对蛋鸡后期血清生化指标的影响

血清生化指标能够反映机体肝脏功能、脂质代谢等情况。MCG在体内易水解,且其产物MCFA可直接通过门静脉到达肝脏并被快速分解利用,在改善肥胖、脂代谢和心血管疾病方面都具有良好的功效[1,13]。有学者研究发现,MCG可通过抑制胆汁酸结合蛋白(I-BABP)的表达从而减少小肠对胆汁酸的重吸收,降低血清胆固醇含量[14]。LAB作为动物肠道益生菌的一种,在其生长发育中起着重要作用,具有改善动物血清生化指标的功能[15]。Alaqil等[7]研究发现,在蛋鸡基础饲粮中添加不同水平LAB(1×109、2×109和3×109 CFU/g)均可显著降低蛋鸡血清TG、TC含量和LDL活性,增加血清HDL活性。Cai等[16]在蛋鸡基础饲粮中添加不同水平MCG(0.15、0.30、0.45 g/kg),结果表明,MCG可显著降低蛋鸡血清TC和LDL含量及ALT、ALP、AST活性,升高HDL活性。本试验结果表明,不同水平MCG复合物均可显著降低蛋鸡血清TC和TG的含量;3 g/kg组蛋鸡血清AST和ALT的活性显著减少;1和2 g/kg组蛋鸡血清ALP的活性显著降低。这与前人报道结果类似,表明MCG复合物可促进蛋鸡脂代谢,保护肝脏功能;这可能是通过下调丝氨酸/苏氨酸激酶11、3-羟基-3-甲基戊二酰辅酶A还原酶、AMP活化蛋白激酶催化亚基1/2(PRKAA1/2)和蛋白磷酸酶催化亚基(PPP2CA、PPP2CB和PPP3CA)的mRNA表达来实现的[17]。UREA是动物体内蛋白质分解代谢的主要含氮终产物,反映了机体氨基酸代谢平衡状态[18]。本试验结果表明,添加不同水平MCG复合物均可显著降低蛋鸡血清UREA含量,说明饲粮中添加MCG复合物有助于改善蛋鸡体内氨基酸的合成与代谢。本试验中添加不同水平的MCG复合物对蛋鸡血清中HDL、LDL活性和UA的含量无显著影响,这与Alaqil等[7]和Cai等[16]研究结果有所不同。可能是因为本研究是将MCG和ALB复合添加,两者之间产生了互作,从而导致研究结果与前人有所差异。

3.3 MCG复合物对蛋鸡后期肠道形态的影响

小肠可分解利用机体摄入的大部分营养物质,VH、CD和VH/CD是评价小肠功能强弱的重要依据,小肠绒毛可增加肠壁与食糜接触面,VH越大接触面积越大;CD可促进小肠上皮细胞成熟,越浅其成熟率越高;VH/CD可表明小肠总体功能情况,其比值越高,小肠功能越强[19-20]。Cai等[16]研究表明,蛋鸡饲粮中加入0.3 g/kg MCG可显著提高空肠VH、VH/CD和十二指肠VH、CD,但对回肠肠道形态无显著影响。Lv等[21]研究发现,蛋鸡饲粮中添加LAB可改善空肠VH和回肠VH/CD,显著增加蛋鸡十二指肠VH和VH/CD。本试验结果表明,不同水平MCG复合物均可显著提升蛋鸡十二指肠VH和VH/CD,降低CD;1和2 g/kg组蛋鸡空肠CD显著降低;试验组蛋鸡空肠VH/CD显著提高。这与前人研究结果相似,表明MCG复合物可改善蛋鸡肠道形态,促进肠道对营养物质的消化与吸收。有学者发现,在动物饮食中添加适量的MCG可增加肠道内菌群α-多样性,增加乳酸杆菌等在肠道内的定植,抑制大肠杆菌等菌群增殖,还可改善由高脂饮食引起的肠道VH降低和CD提高[22-23]。Liu等[23]研究表明,LAB可通过增加肠道益生菌丰度,微调肠道干细胞功能,促进上皮增殖,进而增加VH和黏膜吸收面积。通过上述学者研究推断MCG复合物改善肠道形态原理是:MCG优化了肠道菌群结构,增加了乳酸杆菌等有益菌的丰度,LAB调节肠道干细胞促进肠道上皮细胞的增殖,从而维持肠道环境稳态,改善了蛋鸡肠道形态。本试验中,添加MCG对蛋鸡空肠VH、回肠VH、CD、VH/CD均无显著影响,这与Lv等[21]研究结果有所差异,但与Cai等[16]研究结果相似,推测其原因是不同添加物质作用于蛋鸡的肠道部位不同。

3.4 MCG复合物对蛋鸡后期肠道菌群的影响

肠道菌群与人体健康密切相关,其在机体物质吸收、机体代谢、免疫应答中起着关键作用[24]。大肠杆菌引起的疾病在畜禽上比较常见,尤其是鸡较易感染,其可使蛋鸡无法达到产蛋高峰、产卵期延迟,甚至感染多种继发性疾病[25]。沙门氏菌对蛋鸡的危害同样巨大,其作为食源性疾病主要原因之一,入侵感染蛋鸡后会进入蛋鸡卵巢和输卵管部位,造成细菌沉积,从而感染还未发育成熟鸡蛋,对鸡生产性能和人体健康有着巨大危害[26]。有研究报道,将MCG作为饲粮添加剂饲喂蛋鸡,可显著降低盲肠沙门氏菌数量[27]。Lee等[28]在蛋鸡基础饲粮中添加不同水平微囊化有机酸与MCFA复合物(0.01%、0.05%、0.2%),发现其可增加蛋鸡粪便中LAB数量,减少大肠杆菌数量。Miyamoto等[29]从蛋鸡阴道和泄殖腔内分离出LAB对沙门氏菌做体外抑菌试验发现,LAB对沙门氏菌具有广泛的抑制性。Forte等[30]在蛋鸡基础饲粮中添加0.1%嗜酸乳杆菌做饲养试验发现,LAB可显著降低肠道内大肠杆菌、葡萄球菌等有害菌群的丰度,改善肠道菌群结构。本试验结果表明,3 g/kg组十二指肠内大肠杆菌的数量显著降低;2 g/kg组空肠、盲肠中大肠杆菌数量显著降低;2和3 g/kg组十二指肠沙门氏菌数量显著降低;1 g/kg组回肠中沙门氏菌数量显著降低。从本试验结果可看出,MCG复合物在不同肠道部位对大肠杆菌和沙门氏菌均有一定的抑制作用,这与上述研究结果相似,表明MCG复合物可改善蛋鸡肠道菌群结构,促进蛋鸡机体健康。但本试验对回肠大肠杆菌和空肠、盲肠沙门氏菌数量无显著影响,可能与MCG复合物添加剂量和添加比例有关,两者最适宜添加比例还待进一步研究。

4 结论

饲粮中添加MCG复合物有助于提高蛋鸡后期生产性能,改善血清生化指标,有助于优化其肠道形态,调节肠道菌群结构。综合其经济效益考虑,在本试验条件下,MCG复合物最适宜添加量为1 g/kg。

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