Comparative Study on Effects of Chitosan and Artemisia ordosica Crude Polysaccharide on Rumen Fermentation and Nutrient Degradation Rate of Dairy Cows by in Vitro Method

ZHENG Jie; ZHAO Haoxiang; ZHANG Ting; JIA Yuda; CHANG Hongbo; GUO Yongmei; GUO Xiaoyu; ZHAO Yanli; ZHENG Qingyue; YAN Sumei

doi:10.12418/CJAN2025.279

2025 , Vol. 37 >Issue 5: 3395 - 3405

DOI: https://doi.org/10.12418/CJAN2025.279

RESEARCH PAPER

Comparative Study on Effects of Chitosan and Artemisia ordosica Crude Polysaccharide on Rumen Fermentation and Nutrient Degradation Rate of Dairy Cows by in Vitro Method

ZHENG Jie ,
ZHAO Haoxiang ,
ZHANG Ting ,
JIA Yuda ,
CHANG Hongbo ,
GUO Yongmei ,
GUO Xiaoyu ,
ZHAO Yanli ,
ZHENG Qingyue ,
YAN Sumei ^,^*

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

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

Received date: 2024-11-14

Online published: 2025-05-14

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Abstract

The purpose of this study was to compare the effects of dietary chitosan and Artemisia ordosica crude polysaccharide on rumen fermentation and nutrient degradation rate of dairy cows in the pre-partum period, post-partum period and per-lactation period by in vitro method, and to provide reference for the application of chitosan and Artemisia ordosica crude polysaccharide in dairy cows. Using a single factor completely randomized experimental design, each 3 cows in the pre-partum period, post-partum period and per-lactation period were selected as rumen fluid donors, and the rumen fluid was collected from the oral cavity, filtered by 2 layers of gauze and mixed to prepare culture fluid. The total mixed rations of different periods were collected as fermentation substrates, the fermentation substrate in the control group (CN group) was not added with additives, and that in the chitosan group (CT group) and the Artemisia ordosica crude polysaccharide group (AM group) was added with 0.15% chitosan and 0.1% Artemisia ordosica crude polysaccharide based on the substrate in CN group, respectively, with 6 replicates per group. Nutrient degradation rate and rumen fermentation parameters were measured after culture in vitro for 48 h in the pre-partum period and 24 h in the other periods. The results showed as follows: in the pre-partum period, post-partum period and per-lactation period, the dry matter (DM) degradation rate and contents of microbial protein (MCP), ammonia nitrogen (NH₃-N), acetic acid and total volatile fatty acids in AM and CT groups were significantly higher than those in CN group (P<0.05); the crude protein (CP) degradation rate in AM group was significantly higher than that in CT and CN groups (P<0.05), and which in CT group was significantly higher than CN group (P<0.05). In the pre-partum period and per-lactation period, the ether extract (EE) degradation rate in AM group was significantly higher than that in CN and CT groups (P≤0.05), the contents of propionic acid and butyric acid in CT group were significantly higher than those in CN group (P<0.05), and the isobutyric acid content in AM and CT groups was significantly higher than that in CN group (P<0.05). In the pre-partum period and post-partum period, the gas production in AM group was significantly higher than that in CT and CN groups (P<0.05). In the pre-partum period, the acid detergent fiber (ADF) degradation rate in AM group was higher than that in CN and CT groups (P=0.063). In the post-partum period, the degradation rates of EE and neutral detergent fiber (NDF) in AM and CT groups were significantly higher than those in CN group (P<0.05), and the EE degradation rate in AM group were significantly higher than that in CT group (P<0.05). In the per-lactation period, the gas production in AM and CT groups was significantly higher than that in CN group (P<0.05), and the contents of valeric acid and isovaleric acid in AM and CT groups were significantly higher than those in CN group (P<0.05). In the pre-partum period and post-partum period, the multiple-factors associative effects index (MFAEI) in AM group was slightly higher than that in CT group; in the per-lactation period, the MFAEI in CT group was slightly higher than that in AM group. In conclusion, both chitosan and Artemisia ordosica crude polysaccharide can promote the rumen fermentation of dairy cows in vitro and improve the nutrient degradation rate, and the degradation effect of Artemisia ordosica crude polysaccharide on CP and EE is better than that of chitosan.

Key words： chitosan; Artemisia ordosica crude polysaccharide; dairy cows; rumen fermentation in vitro; nutrient degradation rate

Cite this article

ZHENG Jie , ZHAO Haoxiang , ZHANG Ting , JIA Yuda , CHANG Hongbo , GUO Yongmei , GUO Xiaoyu , ZHAO Yanli , ZHENG Qingyue , YAN Sumei . Comparative Study on Effects of Chitosan and Artemisia ordosica Crude Polysaccharide on Rumen Fermentation and Nutrient Degradation Rate of Dairy Cows by in Vitro Method[J]. Chinese Journal of Animal Nutrition, 2025 , 37(5) : 3395 -3405 . DOI: 10.12418/CJAN2025.279

奶牛在围产期和泌乳期由于妊娠、分娩和泌乳消耗大量能量,当能量摄取无法满足自身需要时,容易发生能量负平衡和一系列代谢疾。瘤胃是奶牛最重要的消化器官,饲粮进入瘤胃后经过微生物降解和一系列复杂的生化反应后生成大量的营养物质,供给奶牛自身代谢和产奶^[1]。瘤胃发酵水平是影响奶牛营养物质降解和消化的重要因素,与奶牛生产性能密切相关^[2]。

壳聚糖作为一种无毒、无副作用的绿色添加剂,可调控瘤胃发酵模式,并调节瘤胃微生物区系平衡,从而提高纤维物质的表观消化率^[3]。研究表明,壳聚糖可以降低绵羊、肉牛^[4]和泌乳奶牛^[5]瘤胃液中乙酸/丙酸值,从而改变瘤胃发酵模式。Dias等^[6]研究发现,壳聚糖可以显著提高肉牛对粗蛋白质(CP)和中性洗涤纤维(NDF)的消化率。本课题组前期研究表明,饲粮中添加1 500 mg/kg壳聚糖能够显著提高奶牛产奶量以及乳蛋白质和乳糖产量,降低体细胞数^[7]。还有研究指出,黄芪多糖、诺丽果多糖和苜蓿多糖等植物多糖均具有提高营养物质消化率、促进动物生长以及提高机体免疫和抗氧化功能的作用^[8-10]。黑沙蒿是一种菊科蒿属草本植物,主要分布在我国西北部地区,而黑沙蒿提取物富含黄酮类、挥发油、多糖和香豆素类等活性成分,不仅具有纯天然、无公害、无残留和价格低廉等优点,还能发挥抗生素替代品的作用^[11]。李书仪等^[12]体外瘤胃发酵试验发现,添加0.30%黑沙蒿多糖可以显著提高瘤胃液中丙酸和菌体蛋白(MCP)含量并抑制瘤胃原虫增殖,改善绒山羊瘤胃发酵环境。刘锦涛等^[13]通过奶牛体外瘤胃发酵试验发现,饲粮中添加黑沙蒿水提物能够显著提高总挥发性脂肪酸(TVFA)、乙酸、丙酸和戊酸含量。然而,目前关于壳聚糖和黑沙蒿粗多糖调控奶牛瘤胃发酵和营养物质降解的比较研究报道较少。体外法模拟瘤胃发酵,具有省时省力、操作简单等优点,可在一定程度上重现瘤胃内的消化过程。奶牛在不同生理时期,体内瘤胃发酵环境会发生不同程度的改变,因此,采集不同时期奶牛的瘤胃液,并将相应时期的全混合日粮作为发酵底物,可以更好地模拟其发酵情况。鉴于此,本试验分别采集处于围产前期、围产后期和泌乳前期的奶牛瘤胃液,利用体外法比较研究壳聚糖和黑沙蒿粗多糖对其瘤胃发酵和营养物质降解率的影响,旨在为在生产实践中有效开发并合理利用壳聚糖和黑沙蒿粗多糖提供依据,对改善奶牛健康进而提高产奶性能具有重要的理论和实践价值。

1 材料与方法

1.1 试验材料

试验选用的壳聚糖为市售产品,其脱乙酰度为85%,黏度为80 cps。黑沙蒿粗多糖采用Xing等^[14]的方法进行制备,所得黑沙蒿粗多糖中多糖含量为52.65%,酚类化合物含量为0.11%,提取率为5.56%。

1.2 瘤胃液供体动物与试验设计

本试验遵循内蒙古农业大学实验动物福利与伦理委员会的指导方针(审批机构:内蒙古农业大学;审批编号:[2019]040),分别选取围产前期[产前(16±5) d]、围产后期[产后(15±7) d,产奶量(35.40±2.42) kg/d]和泌乳前期[产后(40±14) d,产奶量(44.67±2.28) kg/d]的经产荷斯坦奶牛各3头,作为相应研究阶段的瘤胃液供体动物;于晨饲前使用瘤胃液采样器通过口腔采集瘤胃液,将3头牛的瘤胃液进行混合,用于制备培养液。每期的体外发酵底物组成及营养水平见表1。

表1 体外发酵底物组成及营养水平(干物质基础)

Table 1 Composition and nutrient levels of substrates in vitro fermentation (DM basis) %

项目Items	围产前期Pre-partum period	围产后期Post-partum period	泌乳前期Pre-lactation period
原料Ingredients
玉米青贮Corn silage	20.70	28.30	28.30
燕麦草Oat grass	46.57
苜蓿Alfalfa		13.58	13.58
压片玉米Flaked corn		11.62	10.91
豆粕Soybean meal	16.35	15.33	15.23
玉米蛋白粉Corn gluten meal		1.66	1.66
双低菜籽粕Double-low rapeseed meal		2.90	2.87
棉籽Cottonseed		2.92	2.83
啤酒糟Brewer's grain	2.50	6.79	6.79
棕榈油Palm oil		1.20	1.17
玉米粉Corn meal	6.65	11.36	11.66
玉米Corn	5.99
小苏打Baking soda		1.36	1.66
石粉Limestone		0.58	0.68
磷酸氢钙CaHPO₄		0.49	0.59
氧化镁MgO		0.42	0.52
氧化钠Na₂O		0.49	0.55
过瘤胃蛋氨酸Rumen-protected methionine	0.13
过瘤胃氯化胆碱Rumen protected choline chloride	0.11
预混料Premix¹⁾	1.00	1.00	1.00
合计Total	100.00	100.00	100.00
营养水平Nutrient levels²⁾
泌乳净能NE_L/(MJ/kg)	6.40	7.07	7.07
粗蛋白质CP	15.10	17.80	17.80
粗脂肪EE	3.80	4.55	4.55
中性洗涤纤维NDF	45.00	36.00	36.00
酸性洗涤纤维ADF	27.00	22.00	22.00
钙Ca	0.62	1.01	0.90
磷P	0.41	0.40	0.40

	1)每千克预混料含有 Each kilogram of the premix contained:VA 600 000 IU,VD 240 000 IU,VE 3 000 IU,Fe 2.25 g,Cu 0.6 g,Zn 4.5 g,Mn 1.5 g,I 0.15 g,Se 18 mg,Co 30 mg。
	2)泌乳净能参考NY/T 34—2004计算,其他为实测值。NE_L was calculated referred to NY/T 34—2004, while the others were measured values.

本试验采用单因素完全随机试验设计,分为3个组,对照组(CN组)发酵底物不加添加剂,壳聚糖组(CT组)在CN组发酵底物中添加0.15%壳聚糖,黑沙蒿粗多糖组(AM组)在CN组发酵底物中添加0.1%黑沙蒿粗多糖,每组6个重复;围产前期体外培养48 h,其余时期体外培养24 h后测定瘤胃发酵参数和营养物质降解率。壳聚糖和黑沙蒿粗多糖的添加剂量由本课题组前期研究得出,其中壳聚糖的添加剂量参考Zheng等^[7],黑沙蒿粗多糖的添加剂量参考刘锦涛等^[13]。

1.3 瘤胃液的采集与制备

晨饲前使用瘤胃液采集器通过口腔采集奶牛瘤胃液,置于预先预热到39 ℃并通有二氧化碳(CO₂)气体的保温瓶中。返回实验室后,瘤胃液经2层纱布过滤后置于预热到39 ℃并通有CO₂气体的保温瓶中,待用。

1.4 缓冲液配制

体外瘤胃营养物质降解的Kansas缓冲液包括溶液A(KH₂PO₄ 10 g、MgSO₄·7H₂O 0.5 g、NaCl 0.5 g、CaCl₂·2H₂O 0.1 g)和溶液B(Na₂CO₃ 15 g、Na₂S·9H₂O 1 g),参考杜霞^[15]的方法配制;体外瘤胃发酵缓冲液参考Menke等^[16]的方法配制。将上述溶液在水浴锅中温热到39 ℃,持续通入CO₂备用。

1.5 测定指标及方法

1.5.1 常规营养成分含量

干物质(DM)、CP、粗脂肪(EE)、NDF、酸性洗涤纤维(ADF)、钙(Ca)和磷(P)含量分别参照GB/T 6435—2014、GB/T 6432—2018、GB/T 6433—2006、GB/T 20806—2022、NY/T 1459—2022、GB/T 6436—2018和GB/T 6437—2018中方法测定。

1.5.2 体外瘤胃营养物质降解率

在发酵罐中加入266 mL缓冲溶液B和1 330 mL缓冲溶液A,将装有缓冲溶液的发酵罐放置于恒温水浴锅中,平衡温度至39 ℃,并通入CO₂气体2 h;每个发酵罐中加入400 mL瘤胃液混匀,并通入CO₂气体30 s;称取6 g发酵底物于尼龙袋中,平铺于发酵罐中,每个处理6个重复,该操作全程冲入CO₂气体;将发酵罐放置于体外模拟培养箱中培养。分别测定降解前的底物与降解后残渣中DM、CP、EE、NDF和ADF含量,其中NDF和ADF含量采用全自动纤维分析仪(200i,ANKOM,美国)进行测定。体外瘤胃某营养物质降解率计算公式如下:

$ X(\%)=100 \times\left(W_{1} \times A-W_{2} \times B\right) /\left(W_{1} \times A\right)$

式中:X为体外瘤胃某营养物质降解率(%);A为降解前底物中某营养物质含量(%);W₁为降解前底物重量(g);W₂为经体外发酵降解后的残渣重量(g);B为降解残渣中某营养物质含量(%)。

1.5.3 体外瘤胃发酵参数

称取1.00 g发酵底物置于发酵瓶中备用。将经过过滤处理过的瘤胃液与配制好的Menke缓冲液以1∶2的比例混合,将混合后的液体分装到各发酵瓶中60 mL,整个过程通入稳定的CO₂气体,立即连接到AGRS-Ⅲ全自动产气记录仪,39 ℃连续培养,并记录产气量;发酵结束后将发酵瓶置于冰上进行冷却,终止发酵。分别采用pH计测定瘤胃液pH,采用考马斯亮蓝法^[17]测定瘤胃液中MCP含量,采用比色法^[18]测定瘤胃液中氨态氮(NH₃-N)含量;参考王加启^[19]的方法进行原虫计数;采用气相色谱仪(岛津GC-2014)测定挥发性脂肪酸(VFA)含量^[20],以二乙基丁酸为内标,计算TVFA含量。

1.5.4 多项组合效应指数(multiple-factors associative effects index,MFAEI)

MFAEI是多项不同处理的各指标单项组合效应指数(single-factor associative effects index,SFAEI)之和。计算公式如下:

$ \begin{array}{c}\mathrm{SFAEI}=\frac{\sum_{n=1}^{n} \left(A_{2 m}-A_{1 m}\right) / n}{A_{2 m}} \\\mathrm{MFAEI}=\sum \mathrm{SFAEI}\end{array}$

式中:m代表各发酵时间点;n代表发酵时间点的总次数;A₁_m代表CN组各单一指标n个发酵时间点的值;A₂_m表示试验组各单一指标n个发酵时间点的值。

1.6 数据处理

试验数据采用Excel 2021进行初步整理与计算,然后使用SAS 9.0软件进行单因素方差分析和LSD多重比较,结果数据采用平均值和均值标准误(SEM)表示,P≤0.05表示差异显著,0.05<P<0.10表示差异有显著趋势。

2 结果

2.1 壳聚糖和黑沙蒿粗多糖对奶牛体外瘤胃营养物质降解率的影响

由表2可知,围产前期、围产后期和泌乳前期,AM组和CT组DM降解率显著高于CN组(P<0.05),且AM组和CT组间差异不显著(P>0.05);3组间CP降解率差异显著(P<0.05),其中AM组最高,CT组和CN组依次降低。围产后期,3组间EE降解率差异显著(P<0.05),其中AM组最高,CT组和CN组依次降低;围产前期和泌乳前期,AM组EE降解率显著高于CN组和CT组(P≤0.05),CN组和CT组间差异不显著(P>0.05)。围产后期和泌乳前期,AM组和CT组NDF降解率显著高于CN组(P<0.05),且AM组和CT组间差异不显著(P>0.05)。围产前期,AM组ADF降解率有高于CN组和CT组的趋势(P=0.063),且CN组和CT组间差异不显著(P>0.05)。围产后期,AM组和CT组ADF降解率显著高于CN组(P<0.05),且AM组和CT组间差异不显著(P>0.05)。

表2 壳聚糖和黑沙蒿粗多糖对奶牛体外瘤胃营养物质降解率的影响

Table 2 Effects of chitosan and Artemisia ordosica crude polysaccharide on nutrient degradation rate in rumen of dairy cows in vitro %

项目Items		干物质DM	粗蛋白质CP	粗脂肪EE	中性洗涤纤维NDF	酸性洗涤纤维ADF
围产前期Pre-partum period
组别Groups	CN	61.91^b	76.93^c	57.69^b	29.68	23.23
	AM	64.02^a	80.45^a	59.10^a	32.68	26.15
	CT	62.38^a	78.65^b	56.08^b	31.65	23.42
均值标准误SEM		0.67	0.36	1.67	1.23	0.76
P值P-value		0.008	<0.001	0.050	0.289	0.063
围产后期Post-partum period
组别Groups	CN	70.41^b	75.76^c	28.35^c	21.96^b	13.68^b
	AM	74.79^a	82.03^a	43.98^a	33.33^a	20.72^a
	CT	73.73^a	79.54^b	35.63^b	31.26^a	20.80^a
均值标准误SEM		0.78	1.71	1.41	0.78	0.68
P值P-value		0.002	0.001	<0.001	<0.001	<0.001
泌乳前期Pre-lactation period
组别Groups	CN	71.71^b	76.43^c	51.92^b	31.77^b	22.84
	AM	74.94^a	83.98^a	66.21^a	38.79^a	21.75
	CT	73.45^a	80.04^b	52.72^b	36.46^a	22.97
均值标准误SEM		0.50	0.55	2.63	1.03	1.74
P值P-value		0.001	<0.001	0.040	0.004	0.865

	同列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和表4同。
	In the same column, values with no letter or the same letter superscripts mean no significant difference (P>0.05), while different letter superscripts mean significant difference (P≤0.05). The same as Table 3 and Table 4.

2.2 壳聚糖和黑沙蒿粗多糖对奶牛体外瘤胃发酵的影响

由表3可知,围产后期和泌乳前期,与CN组相比,CT组pH有降低趋势(P=0.093,P=0.078),AM组pH与CN组和CT组相比均无显著差异(P>0.05)。围产前期和围产后期,AM组产气量显著高于CT组和CN组(P<0.05),且CT组和CN组间差异不显著(P>0.05);泌乳前期,AM组和CT组产气量显著高于CN组(P<0.05),且AM组和CT组间差异不显著(P>0.05)。各时期,AM组和CT组MCP和NH₃-N含量显著高于CN组(P<0.05),且AM组和CT组间差异均不显著(P>0.05)。

表3 壳聚糖和黑沙蒿粗多糖对奶牛体外瘤胃发酵参数的影响

Table 3 Effects of chitosan and Artemisia ordosica crude polysaccharide on rumen fermentation parameters of dairy cows in vitro

项目Items		pH	产气量Gas production/mL	菌体蛋白MCP/(mg/dL)	氨态氮NH₃-N/(mg/dL)	原虫Protozoan/(×10⁴个/mL)
围产前期Pre-partum period
组别Groups	CN	6.32	103.39^b	28.615^b	1.70^b	2.33
	AM	6.29	123.97^a	32.21^a	1.84^a	1.75
	CT	6.30	104.39^b	30.84^a	1.84^a	1.50
均值标准误SEM		0.02	3.02	0.83	0.03	0.23
P值P-value		0.700	0.001	0.025	0.024	0.059
围产后期Post-partum period
组别Groups	CN	6.42	113.78^b	22.10^b	2.78^b	2.10
	AM	6.40	120.47^a	32.76^a	2.91^a	1.75
	CT	6.36	114.56^b	31.21^a	2.91^a	2.29
均值标准误SEM		0.02	1.41	1.26	0.04	0.17
P值P-value		0.093	0.008	<0.001	0.007	0.168
泌乳前期Pre-lactation period
组别Groups	CN	6.43	103.76^b	26.00^b	1.96^b	2.10
	AM	6.42	121.60^a	36.86^a	2.16^a	2.50
	CT	6.33	121.51^a	34.21^a	2.17^a	2.33
均值标准误SEM		0.03	2.99	1.66	0.04	0.30
P值P-value		0.078	0.001	<0.001	0.006	0.646

由表4可知,围产前期、围产后期和泌乳前期,与CN组相比,AM组和CT组乙酸和TVFA含量显著提高(P<0.05),且CT组和AM组间差异不显著(P>0.05)。围产前期和泌乳前期,与CN组相比,CT组丙酸和丁酸含量显著提高(P<0.05),AM组与CN组和CT组间均无显著差异(P>0.05)。围产前期和泌乳前期,与CN组相比,AM组和CT组异丁酸含量显著提高(P<0.05),且CT组和AM组间差异不显著(P>0.05)。围产前期,与AM组相比,CT组乙酸/丙酸值有降低趋势(P=0.061),但各组间均无显著差异(P>0.05)。围产后期,与CN组相比,CT组乙酸/丙酸值显著提高(P<0.05),AM组与CN组和CT组间均无显著差异(P>0.05)。泌乳前期,CN组相比,AM组和CT组戊酸和异戊酸含量显著提高(P<0.05),且CT组和AM组间差异不显著(P>0.05)。

表4 壳聚糖和黑沙蒿粗多糖对奶牛体外瘤胃发酵VFA含量的影响

Table 4 Effects of chitosan and Artemisia ordosica crude polysaccharide on VFA contents in rumen fermentation of dairy cows in vitro

项目Items		乙酸Acetic acid/(mmol/L)	丙酸Propionic acid/(mmol/L)	丁酸Butyric acid/(mmol/L)	异丁酸Isobutyric acid/(mmol/L)	戊酸Valeric acid/(mmol/L)	异戊酸Isovaleric acid/(mmol/L)	乙酸/丙酸Acetic acid/propionic acid	总挥发性脂肪酸TVFA/(mmol/L)
围产前期Pre-partum period
组别Groups	CN	42.61^b	16.12^b	8.31^b	0.62^b	1.05	1.18	2.51	69.91^b
	AM	45.37^a	16.91^ab	8.52^ab	0.68^a	1.07	1.20	2.55	73.77^a
	CT	45.39^a	17.36^a	8.76^a	0.69^a	1.06	1.20	2.44	74.47^a
均值标准误SEM		0.53	0.29	0.08	0.01	0.01	0.01	0.03	0.79
P值P-value		0.026	0.027	0.006	0.014	0.397	0.497	0.061	0.002
围产后期Post-partum period
组别Groups	CN	40.21^b	17.34	11.06	0.93	1.70	1.77	2.33^b	73.01^b
	AM	44.93^a	18.63	11.03	0.90	1.73	1.74	2.41^ab	78.97^a
	CT	46.24^a	18.05	11.67	0.92	1.82	1.74	2.57^a	80.73^a
均值标准误SEM		0.76	0.50	0.23	0.01	0.05	0.02	0.06	1.13
P值P-value		<0.001	0.217	0.119	0.308	0.310	0.086	0.033	<0.001
泌乳前期Pre-lactation period
组别Groups	CN	43.48^b	17.34^b	7.65^b	7.08^b	1.36^b	1.39^b	2.51	78.30^b
	AM	49.03^a	19.37^ab	10.27^ab	8.00^a	1.56^a	1.58^a	2.53	89.80^a
	CT	52.99^a	21.68^a	11.56^a	8.32^a	1.63^a	1.73^a	2.46	97.91^a
均值标准误SEM		1.78	0.94	0.92	0.01	0.05	0.15	0.04	3.52
P值P-value		0.006	0.017	0.026	<0.001	0.007	0.003	0.497	0.005

2.3 壳聚糖和黑沙蒿粗多糖对奶牛体外瘤胃发酵MFAEI的影响

由表5可知,围产前期和围产后期,与CN组相比,CT组和AM组MFAEI均大于0,其中AM组略高于CT组;泌乳前期,与CN组相比,CT组和AM组的MFAEI均大于0,其中CT组略高于AM组。

表5 壳聚糖和黑沙蒿粗多糖的SFAEI和MFAEI

Table 5 SFAEI and MFAEI of chitosan and Artemisia ordosica crude polysaccharide

项目Items		组别Groups
项目Items		CN	AM	CT
围产前期Pre-partum period
单项组合效应指数SFAEI	菌体蛋白MCP	0.00	0.11	0.07
	氨态氮NH₃-N	0.00	0.07	0.07
	总挥发性脂肪酸TVFA	0.00	0.05	0.06
	产气量Gas production	0.00	0.17	0.01
多项组合效应指数MFAEI		0.00	0.40	0.21
围产后期Post-partum period
单项组合效应指数SFAEI	菌体蛋白MCP	0.00	0.33	0.29
	氨态氮NH₃-N	0.00	0.05	0.05
	总挥发性脂肪酸TVFA	0.00	0.08	0.09
	产气量Gas production	0.00	0.06	0.01
多项组合效应指数MFAEI		0.00	0.52	0.44
泌乳前期Pre-lactation period
单项组合效应指数SFAEI	菌体蛋白MCP	0.00	0.29	0.24
	氨态氮NH₃-N	0.00	0.09	0.10
	总挥发性脂肪酸TVFA	0.00	0.13	0.20
	产气量Gas production	0.00	0.15	0.15
多项组合效应指数MFAEI		0.00	0.66	0.69

3 讨论

3.1 壳聚糖和黑沙蒿粗多糖对奶牛体外瘤胃营养物质降解率的影响

饲粮营养物质的瘤胃降解率反映了营养物质在瘤胃内的降解情况,是影响反刍动物生产性能的重要因素之一。目前,关于壳聚糖或黑沙蒿多糖对反刍动物体外瘤胃营养物质降解率的研究报道很少,将二者的影响效果进行比较的研究尚未见相关报道。李魏^[21]研究指出,山羊饲粮中添加0.12%壳聚糖,能够显著提高山羊体外瘤胃NDF降解率。Li等^[22]研究发现,黑沙蒿粗多糖能显著提高绒山羊DM、CP和NDF降解率。丁国和^[23]研究表明,饲粮中添加3 mg猪毛蒿提取物能够显著提高奶山羊DM降解率。本试验中,在泌乳前期、围产前期和围产后期饲粮中添加黑沙蒿粗多糖的AM组以及添加壳聚糖的CT组奶牛体外瘤胃多种营养物质(DM、CP和NDF)降解率相较于CN组均有所提升,且AM组CP和EE降解率显著高于CT组,这说明壳聚糖和黑沙蒿粗多糖均可促进奶牛的体外瘤胃营养物质降解率,且对于CP和EE的降解率,黑沙蒿粗多糖的促进效果更佳。

3.2 壳聚糖和黑沙蒿粗多糖对奶牛体外瘤胃发酵的影响

优化瘤胃发酵对提高反刍动物饲料利用率有重要意义。VFA是瘤胃微生物利用碳水化合物发酵后的主要产物,为反刍动物提供了70%~80%的能量,其含量和组成代表了瘤胃的发酵水平与供能效率。本试验中,在围产前期、围产后期和泌乳前期饲粮中分别加入壳聚糖和黑沙蒿粗多糖后,乙酸和TVFA含量显著升高,说明二者在体外试验中均能增加供能的底物,且壳聚糖的促进效果略优。在围产前期和泌乳前期,饲粮中添加壳聚糖后还可显著提高丙酸含量,丙酸是VFA中供能效率最高的,说明壳聚糖还具有优化瘤胃发酵类型的潜力。Mingoti等^[24]研究发现,壳聚糖可以提高奶牛瘤胃中丙酸含量,且提升程度随壳聚糖含量提高呈线性增加。梁高沣等^[25]研究表明,壳聚糖可提高丙酸产量,降低乙酸/丙酸值。刘锦涛等^[13]研究结果发现,黑沙蒿水提物添加组体外瘤胃发酵液中TVFA、乙酸、丙酸和戊酸含量显著提高。上述结果与本试验结果基本一致。

瘤胃pH是发酵功能正常行使的先决条件,本试验中各组pH为6.29~6.43,处于适宜pH范围内(6.0~7.0)^[26],说明分别添加壳聚糖或黑沙蒿粗多糖不会破坏瘤胃内环境。瘤胃发酵产气量可以直接反映瘤胃发酵的剧烈程度,瘤胃中NH₃-N是MCP合成的主要原料,其含量反映了瘤胃中含氮物的降解程度,而MCP含量反映了瘤胃中微生物利用NH₃-N的能力,二者都是重要的瘤胃发酵指标。Li等^[22]研究发现,饲粮中添加不同剂量的黑沙蒿粗多糖均可促进绒山羊的体外瘤胃发酵,提高NH₃-N和MCP含量。张淑琴^[3]研究表明,壳聚糖可以提高肉牛瘤胃NH₃-N含量,改善肉牛生长后期饲料效率。李魏^[21]在山羊的体内试验中发现,壳聚糖能提高瘤胃MCP含量。本试验比较研究了在围产前期、围产后期和泌乳前期饲粮中单独添加黑沙蒿粗多糖或壳聚糖对奶牛体外瘤胃发酵性能的影响,发现二者均可引起体外瘤胃发酵液中NH₃-N、MCP和TVFA含量显著升高,促进体外瘤胃发酵。此外,在围产前期、围产后期和泌乳前期饲粮中分别添加壳聚糖和黑沙蒿粗多糖,均可提高多项体外发酵参数MFAEI值,这说明二者对奶牛体外瘤胃发酵具有促进效果。

不过,关于壳聚糖和黑沙蒿粗多糖对瘤胃发酵和营养物质降解具有促进效果的机制尚不十分清楚。有研究指出,黑沙蒿粗多糖^[22]和壳聚糖^[27]均能够通过调节瘤胃菌群丰度,进而提高绒山羊瘤胃发酵功能和营养物质消化。Zheng等^[28]研究表明,壳聚糖可以增强硫氧还蛋白还原酶和过氧化氢酶等抗氧化酶活性,通过抑制核因子-κB信号通路,降低促炎症因子的合成。Li等^[22]研究表明,饲粮中添加0.3%黑沙蒿粗多糖可以显著提高绒山羊血清过氧化氢酶、谷胱甘肽过氧化物酶以及总超氧化物歧化酶等抗氧化酶活性。这可能是引起二者增强瘤胃发酵功能的原因。因此,后续有必要从瘤胃菌群的结构变化和抗氧化功能等角度探究其影响机制。本研究发现,分别以围产前期、围产后期和泌乳前期的奶牛作为瘤胃液供体,通过在饲粮中添加0.15%壳聚糖或0.10%黑沙蒿粗多糖均具有促进体外瘤胃发酵和提高营养物质降解率的潜力,但关于其他添加剂量的影响效果尚需进一步探究。

4 结论

壳聚糖和黑沙蒿粗多糖均可改善围产前期、围产后期和泌乳前期奶牛体外瘤胃发酵环境,提高营养物质降解率,相比之下黑沙蒿粗多糖对CP和EE降解的促进效果优于壳聚糖。

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