Chinese Journal of Animal Nutrition >

2026 , Vol. 38 >Issue 2: 1378 - 1392

DOI: https://doi.org/10.12418/CJAN2026.110

RESEARCH PAPER

Meta-Analysis of Dietary Rumen Degradable Starch Regulation on Nutrient Digestion, Rumen Fermentation and Lactation Performance in Dairy Cows

  • SU Xiaodong , 1 ,
  • ZHANG Jun 1, 2 ,
  • WANG Dangdang 1 ,
  • YAO Junhu , 1, 2, *
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  • 1 College of Animal Science and Technology, Northwest A&F University, Yangling 712100, China
  • 2 National Central of Technology Innovation for Dairy, Hohhot 010100, China
* professor, E-mail:

Received date: 2025-05-16

  Online published: 2026-02-12

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Abstract

This study aimed to quantitatively evaluate the effects of rumen degradable starch (RDS) on nutrient digestion, rumen fermentation, and lactation performance in dairy cows using a Meta-analysis approach. A systematic literature search was performed across the PubMed, Web of Science, and Science Direct databases, and a total of 83 eligible publications involving 328 datasets were finally included. The results showed that: 1) grain species and processing methods significantly affected the digestive characteristics of dietary starch (P<0.05). Among different grains, wheat had the highest ruminal starch degradability (81.33%), whereas corn exhibited the lowest value (54.73%). Compared with dry-ground, dry-rolled and steam-flaked treatments, high-moisture treatment resulted in the highest ruminal starch degradability and total-tract starch digestibility in corn-based diets. In addition, steam-flaked treatment significantly increased the ruminal starch degradability and total-tract starch digestibility in barley- and sorghum-based diets compared with dry-rolled treatment (P<0.05). 2) The rumen was the primary site for starch digestion. The total-tract starch digestibility was linearly and positively correlated with RDS degradability [coefficient of determination (R2)=0.94, P<0.001], while it was linearly and negatively correlated with the amount of rumen-escape starch (RES) (R2=0.74, P<0.001). The ruminal neutral detergent fiber (NDF) degradability was linearly and negatively correlated with RDS degradation amount (R2=0.87, P<0.001). In contrast, the ruminal nitrogen degradation amount (R2=0.87, P=0.067) and microbial crude protein (MCP) synthesis amount (R2=0.88, P<0.001) were linearly and positively correlated with RDS degradation amount. 3) RDS degradation amount affected lactation performance by regulating the ruminal acetate-to-propionate ratio. With the increase in RDS degradation amount, the ruminal acetate-to-propionate ratio decreased linearly (R2=0.72, P<0.001), the 4% fat-corrected milk (4% FCM) yield increased linearly (R2=0.95, P<0.001), and the milk fat percentage decreased linearly (R2=0.84, P<0.001). Moreover, quadratic relationships were observed between the dietary NDF/RDS and both ruminal acetate-to-propionate ratio (R2=0.77, P<0.001) and milk fat percentage (R2=0.81, P<0.001). In conclusion, dietary RDS improves milk yield by promoting ruminal propionate-type fermentation, but excessive RDS inhibits fiber degradation and milk fat synthesis. Therefore, optimizing the dietary carbohydrate structure is essential to balance rumen health and lactation performance in dairy cows.

Key words： dairy cows; Meta-analysis; rumen degradable starch; carbohydrate balance index; lactation performance

Cite this article

SU Xiaodong , ZHANG Jun , WANG Dangdang , YAO Junhu . Meta-Analysis of Dietary Rumen Degradable Starch Regulation on Nutrient Digestion, Rumen Fermentation and Lactation Performance in Dairy Cows[J]. Chinese Journal of Animal Nutrition, 2026 , 38(2) : 1378 -1392 . DOI: 10.12418/CJAN2026.110

淀粉作为高产奶牛的主要能量来源,通常占饲粮干物质的20%~30%[1],其消化代谢过程直接影响奶牛的瘤胃发酵模式、养分利用效率及泌乳性能。其中,在瘤胃中可被微生物降解的淀粉称为瘤胃可降解淀粉(rumen degradable starch,RDS);单位时间内降解的RDS占摄入淀粉总量的百分比称为RDS降解速率;而在滞留时间内降解的RDS占摄入淀粉总量的百分比则定义为RDS降解度,该指标是RDS降解速率与瘤胃滞留时间的函数。RDS降解速率与RDS降解度共同调控瘤胃挥发性脂肪酸(volatile fatty acids,VFA)的生成效率与发酵过程,进而影响奶牛的能量供应和生产性能。淀粉来源及加工方式会影响饲粮RDS含量[2],进而影响奶牛的养分消化、瘤胃健康及泌乳性能。
RDS对瘤胃发酵和泌乳性能的影响具有两面性:一方面,RDS为可降解碳水化合物,能够显著促进瘤胃微生物的丙酸型发酵[3],提高葡萄糖前体供应,优化泌乳能量利用效率[4];另一方面,过量RDS在瘤胃中快速降解会加速酸累积,导致瘤胃pH下降,抑制纤维降解菌活性[5],降低乙酸产量及乙丙比,最终损害乳脂合成[6]。为精准调控RDS代谢平衡,本团队创新性提出碳水化合物平衡指数(carbohydrate balance index,CBI)[7-8],该指数通过量化饲粮中物理有效中性洗涤纤维(physically effective neutral detergent fiber,peNDF)与RDS的比例,综合反映饲粮碳水化合物结构对瘤胃发酵及泌乳性能的影响。
尽管已有大量试验研究了饲粮RDS对奶牛生产性能的影响[9-12],但尚未量化RDS与消化代谢和泌乳性能间的关系。因此,本文通过整合分析已发表的文献数据,采用Meta分析方法量化饲粮RDS与奶牛养分消化、瘤胃发酵及泌乳性能间的关系,以期为优化奶牛饲粮配方精准设计、提高淀粉利用效率提供有效参数。

1 材料与方法

1.1 文献检索与数据收集

以“(rumen degradable starch) OR (duodenal cannula) AND (dairy cow or dairy cattle)”为检索词,系统检索PubMed、Web of Science和Science Direct数据库中发表的相关研究性文章。将检索结果导入EndNote文献管理软件,依据以下纳入标准进行筛选:1)试验对象为泌乳奶牛;2)文献中包含RDS的实测数据。文献检索和筛选流程见图1,最终纳入符合要求的文献83篇,共计328组数据,涉及试验奶牛661头。
图1 Meta分析文献检索和筛选流程图

Fig.1 Literature search and screening flowchart for Meta-analysis

1.2 统计方法

使用R 4.1.2软件中的lme4程序包(https://cran.r-project.org/package=lme4)对获取的数据进行混合模型分析[13-14],采用线性混合效应模型(LMM)分析饲粮中谷物种类和加工方式对奶牛淀粉消化率的影响,并结合方差分析(ANOVA)检验固定效应的显著性;采用Spearman相关分析评估变量间的相关性。模型中以不同试验作为随机效应,谷物种类、加工方式、饲粮养分指标、瘤胃发酵参数和泌乳性能指标作为固定效应。P<0.05表示差异显著。

2 结果与分析

2.1 饲粮中谷物种类和加工方式对奶牛淀粉消化的影响

不同谷物饲粮淀粉在奶牛瘤胃中的降解度和全消化道消化率如表1所示。其中,小麦饲粮淀粉的瘤胃降解度和全消化道消化率最高,玉米饲粮淀粉的瘤胃降解度最低,大麦饲粮淀粉的全消化道消化率最低;且不同谷物饲粮间淀粉全消化道消化率的差异小于其在瘤胃降解度上的差异。
表1 不同谷物饲粮淀粉在奶牛瘤胃中的降解度和全消化道消化率

Table 1 Ruminal degradability and total-tract digestibility of starch in different cereal-based diets for dairy cows %

项目
Items		 玉米
Corn		 小麦
Wheat		 大麦
Barley		 高粱
Sorghum		 均值标准误
SEM		 P值
P-value
重复数n 121 27 65 19
瘤胃降解度Ruminal degradability 54.73c 81.33a 66.53b 73.04b 1.097 <0.001
全消化道消化率Total-tract digestibility 92.70bc 97.09a 90.73c 94.47ab 0.406 <0.001

重复数代表从文献里筛选并收录到数据集中的数据条目数量。同行数据肩标无字母或相同字母表示差异不显著(P>0.05),不同小写字母表示差异显著(P<0.05)。下表同。

n represented the number of independent data entries screened and included in the dataset from relevant literature. In the same row, values with no letter or the same letter superscripts mean no significant difference (P>0.05), while with different small letter superscripts mean significant difference (P<0.05). The same as below.

不同加工方式谷物饲粮淀粉在奶牛瘤胃中的降解度和全消化道消化率如表2所示。对玉米而言,高湿处理玉米饲粮淀粉的瘤胃降解度和全消化道消化率最高。与干碾压处理相比,蒸汽压片处理显著提高了大麦和高粱饲粮的淀粉瘤胃降解度和全消化道消化率(P<0.05)。
表2 不同加工方式谷物饲粮淀粉在奶牛瘤胃中的降解度和全消化道消化率

Table 2 Ruminal degradability and total-tract digestibility of starch in differently processed cereal-based diets for dairy cows %

项目
Items		 干粉碎
Dry-ground		 干碾压
Dry-rolled		 蒸汽压片
Steam-flaked		 高湿
High-moisture		 均值标准误
SEM		 P值
P-value




玉米Corn		 重复数n 93 14 15 4
瘤胃降解度
Ruminal degradability		 52.82b 55.04b 61.91ab 73.65a 1.316 0.007
全消化道消化率
Total-tract digestibility		 93.43a 86.51b 93.00a 95.12a 0.572 0.002




小麦Wheat		 重复数n 20 6 - -
瘤胃降解度
Ruminal degradability		 82.30 80.25 - - 1.537 0.235
全消化道消化率
Total-tract digestibility		 96.98 - - - 0.401 -




大麦Barley		 重复数n - 6 49 -
瘤胃降解度
Ruminal degradability		 - 63.31b 85.23a - 1.774 <0.001
全消化道消化率
Total-tract digestibility		 - 90.86b 95.83a - 0.614 0.021




高粱Sorghum		 重复数n - 4 15 -
瘤胃降解度
Ruminal degradability		 - 54.95b 77.86a - 2.480 <0.001
全消化道消化率
Total-tract digestibility		 - 84.63b 97.09a - 1.257 <0.001

-表示无相关数据。

-indicated no relevant data.

2.2 奶牛各消化部位淀粉消化率

本研究共整合35组奶牛全消化道不同部位淀粉消化率相关数据,描述性统计结果(表3)显示,各消化部位淀粉消化量占摄入量的比例平均值依次为瘤胃71.80%、小肠16.70%、大肠5.15%,全消化道总消化率达93.36%;从部位流通量来看,进入小肠和大肠的淀粉分别有64.65%和55.34%被消化利用。
表3 奶牛各消化部位淀粉消化率的描述性统计

Table 3 Descriptive statistics of starch digestibility by different digestive sites in dairy cows %

项目
Items		 重复数
n		 平均值
Mean		 25%百分位数
P25		 50%百分位数
P50		 75%百分位数
P75
淀粉消化量占摄入量比例Proportion of starch digested relative to intake
瘤胃Rumen 35 71.80 57.40 79.00 86.90
小肠Small intestine 35 16.70 7.02 12.08 27.30
大肠Large intestine 35 5.15 1.96 3.80 7.40
全消化道Total digestive tract 35 93.36 89.20 97.30 98.89
淀粉消化量占流通量比例Proportion of starch digested relative to flow
大肠Large intestine 35 55.34 37.04 60.00 69.23
小肠Small intestine 35 64.65 56.58 70.00 78.00

2.3 奶牛淀粉消化对中性洗涤纤维(NDF)和氮消化的影响

2.3.1 淀粉、NDF和氮的摄入量、瘤胃降解及全消化道消化参数的相关性分析

由图2可知,淀粉摄入量与RDS降解量、RDS降解度及过瘤胃淀粉(rumen-escape starch,RES)量均呈极显著相关(P<0.01);全消化道淀粉消化量与RDS降解量呈极显著相关(P<0.01),全消化道淀粉消化率与RES消化率同样表现为极显著相关(P<0.01)。此外,淀粉摄入量和RDS降解量与瘤胃NDF降解量、瘤胃NDF降解度、瘤胃可降解蛋白(rumen degradable protein,RDP)量和微生物蛋白(microbial protein,MCP)合成量呈极显著相关(P<0.01)。
图2 淀粉、NDF和氮的摄入量、瘤胃降解及全消化道消化参数的相关性分析

RDS:瘤胃可降解淀粉 rumen degradable starch。NDF:中性洗涤纤维 neutral detergent fiber。下图同 the same as below。

*表示显著相关(P<0.05),**表示极显著相关(P<0.01)。* indicated significant correlation (P<0.05), and ** indicated extremely significant correlation (P<0.01).

Fig.2 Correlation analysis of intake, ruminal degradation and total-tract digestibility parameters of starch, NDF and nitrogen

2.3.2 瘤胃、后消化道及全消化道淀粉消化利用的关系

奶牛瘤胃、后消化道和全消化道淀粉消化率的回归分析结果如图3所示。其中,RDS降解量随淀粉摄入量的增加呈二次曲线斜率递减式上升[图3-A,决定系数(R2)=0.91,P<0.001];RDS降解度随淀粉摄入量的增加呈先升高后降低的趋势(图3-B,R2=0.81,P=0.030),在淀粉摄入量为5.5 kg/d时达到峰值;RES量随淀粉摄入量的增加呈二次曲线上升(图3-C,R2=0.86,P<0.001)。全消化道淀粉消化率与RDS降解度呈线性正相关(图3-D,R2=0.94,P<0.001),而与RES量(图3-E,R2=0.74,P<0.001)和RES消化率(图3-F,R2=0.63,P<0.001)呈线性负相关。
图3 奶牛瘤胃、后消化道及全消化道淀粉消化率的回归关系

Fig.3 Regression relationships among ruminal, post-ruminal tract and total-tract starch digestibility in dairy cows

RMSE:均方根误差 root mean squared error。下图同 the same as below。

2.3.3 淀粉消化对瘤胃NDF和氮降解及MCP合成的影响

淀粉、NDF和氮是反刍动物饲粮的核心组分,且三者的消化过程存在互作效应。本研究对淀粉消化与NDF和氮消化相关指标进行了回归分析,结果表明,瘤胃NDF降解度与淀粉摄入量(图4-A,R2=0.85,P<0.001)和RDS降解量(图4-B,R2=0.87,P<0.001)呈线性负相关;而瘤胃氮降解量与淀粉摄入量(图4-E,R2=0.88,P<0.001)和RDS降解量(图4-F,R2=0.87,P=0.067)呈线性正相关;MCP合成量与淀粉摄入量(图4-C,R2=0.87,P<0.001)和RDS降解量(图4-D,R2=0.88,P<0.001)同样呈线性正相关。
图4 奶牛淀粉摄入量和RDS降解量对瘤胃NDF和氮降解及MCP合成影响的回归分析

Fig.4 Regression analysis of effects of starch intake and RDS degradation amount on rumen NDF degradation, nitrogen degradation and MCP synthesis in dairy cows

2.4 RDS降解量及饲粮NDF/RDS对奶牛瘤胃发酵的影响

由图5可知,瘤胃pH和乙丙比与RDS降解量呈线性负相关(P<0.001),而与饲粮NDF/RDS呈现二次曲线关系(P<0.001)。
图5 奶牛RDS降解量和饲粮NDF/RDS对瘤胃乙丙比和pH影响的回归分析

Fig.5 Regression analysis of effects of RDS degradation amount and dietary NDF/RDS on ruminal acetate-to-propionate ratio and pH in dairy cows

2.5 RDS降解量及饲粮NDF/RDS对奶牛泌乳性能的影响

由图6可知,4%乳脂校正乳(4% fat-corrected milk,4% FCM)产量与RDS降解量呈线性正相关(R2=0.95,P<0.001),而与饲粮NDF/RDS呈线性负相关(R2=0.96,P<0.001)。此外,泌乳净能(net energy for lactation,NEL)与RDS降解量呈线性正相关(R2=0.95,P<0.001)。而乳脂率与RDS降解量呈线性负相关(R2=0.84,P<0.001),与饲粮NDF/RDS呈二次曲线关系(R2=0.81,P<0.001)。
图6 奶牛RDS降解量和饲粮NDF/RDS对泌乳性能影响的回归分析

Fig.6 Regression analysis of effects of RDS degradation amount and dietary NDF/RDS on lactation performance in dairy cows

3 讨论

3.1 饲粮中谷物种类和加工方式对奶牛淀粉消化的影响

谷物是反刍动物饲粮中重要的能量来源,其淀粉降解特性直接影响瘤胃发酵模式、VFA的产生以及动物生产性能。瘤胃是淀粉降解的主要场所,谷物的淀粉结构、颗粒大小和加工方式显著影响其在瘤胃中的降解特性。本研究结果显示,不同谷物饲粮中淀粉的瘤胃降解度排序为:小麦>高粱>大麦>玉米。然而,Gómez等[10]报道的反刍动物饲粮中不同谷物淀粉瘤胃降解度排序为:燕麦>小麦>大麦>玉米>高粱;另有研究通过体外产气法测定的淀粉降解率(产气速率)排序为:小麦(0.26 h-1)>大麦(0.24 h-1)>玉米(0.15 h-1)>高粱(0.06 h-1)[15]。相较于小麦和燕麦,玉米和高粱因含有高比例的外围胚乳和角质胚乳,阻碍微生物的附着[16],且其蛋白质基质中醇溶蛋白含量更高,不利于淀粉酶发挥降解作用[17]。值得注意的是,本研究中高粱的淀粉瘤胃降解度高于大麦和玉米,原因在于所收录数据主要来自经蒸汽压片处理的高粱,该加工方式显著提升了其淀粉的可降解性。本研究中结果表明,全消化道淀粉消化率排序为:小麦>高粱>玉米>大麦,与瘤胃降解度基本一致,但不同谷物间差异幅度有所减小,与Owens等[18]的报道相符。这可能是由于在瘤胃中未降解的淀粉进入小肠和大肠后被继续消化,在一定程度上弥合了不同谷物淀粉在瘤胃降解度上的差距。然而,反刍动物小肠对淀粉的消化能力有限[2,19],且其淀粉消化量并不随十二指肠淀粉流量增加而等比例提升[11]。尽管小肠和大肠的后续消化可在一定程度上弥补瘤胃降解的不足,但小肠淀粉消化能力有限,未被小肠消化的过量淀粉进入大肠后经微生物发酵,不仅增加大肠酸中毒的风险[20],还会因大肠降解淀粉的能量利用效率较低(仅为小肠的40%左右)而降低整体能量利用效率[9]。因此,合理选择谷物种类及其加工方式,优化淀粉在瘤胃和小肠中的消化率,对于提高反刍动物的能量利用效率和健康水平至关重要。
玉米富含角质胚乳与醇溶蛋白,需通过加工处理以提升其营养价值。适宜的加工方式可显著破坏籽实结构,提高淀粉可消化性[21],并改变玉米在奶牛消化道中的消化位点与消化程度,进而提升能量利用效率。本研究结果表明,不同加工方式玉米饲粮的淀粉瘤胃降解度排序为:高湿玉米(73.65%)>蒸汽压片玉米(61.91%)>干碾压玉米(55.04%)>干粉碎玉米(52.82%),与Owens等[18]的研究结果相符。其中,干粉碎和干碾压处理通过增大玉米表面积,可促进瘤胃微生物及消化酶与淀粉的接触[22];蒸汽压片技术则结合高温蒸汽调制和机械碾压,可诱导淀粉凝胶化与糊化,破坏蛋白质基质及晶体结构,增强淀粉可消化性[12];高湿处理则通过发酵作用显著提高淀粉瘤胃降解度[23]。值得注意的是,育肥牛相关研究表明,不同加工方式玉米的淀粉瘤胃降解度显著高于奶牛[18],这可能与两者采食量(奶牛采食量更高、瘤胃排空更快)及瘤胃生理功能差异有关。此外,山羊对玉米加工方式的代谢响应与奶牛、育肥牛的差异更为明显——与奶牛和育肥牛需依赖加工玉米不同,山羊对整粒玉米表现出更高的利用效率。本团队前期研究发现,相较于粉碎玉米,饲喂整粒玉米可显著促进羔羊体尺发育[24]和瘤胃发育[25],提高青年羊日增重与饲料效率[26-27],并改善胴体品质及氨基酸平衡[28];同时,整粒玉米还能提高泌乳奶山羊的乳脂率及乳脂产量[29],表明其在小反刍动物生长发育与生产性能调控中具有独特优势。淀粉瘤胃降解度是降解速率与滞留时间共同作用的结果。本团队最新研究表明,造成不同加工方式玉米在奶山羊瘤胃中降解度差异的关键,是奶山羊网瓣胃孔对食糜粒径的选择性通过效应[30]。整粒玉米虽瘤胃降解速率较慢,但由于粒径较大难以通过奶山羊网瓣胃孔,延长了在瘤胃内的降解时间,并通过反刍、咀嚼逐步释放淀粉,最终提升淀粉降解度;破碎或碾压玉米虽降解速率较快,但可快速通过网瓣胃孔,导致瘤胃滞留时间缩短,淀粉降解度最低;而细粉碎玉米在瘤胃内降解速率过快,饲喂量较大时可能降低瘤胃pH,影响纤维降解与瘤胃健康。

3.2 奶牛瘤胃、后消化道及全消化道淀粉消化利用的关系

淀粉摄入量对其消化率具有显著影响[11]。本研究结果表明,RDS降解量并未随淀粉摄入量增加呈线性增加,而是呈二次曲线上升,这一结果与Moharrery等[11]的研究一致。淀粉摄入量的负面效应可能与干物质采食量(DMI)有关,淀粉与干物质摄入量的增加会加快瘤胃排空速率,进而缩短淀粉在瘤胃内的滞留时间。有研究表明,DMI每增加1 kg,非纤维碳水化合物的消化量降低12 g[31]。本研究对RDS降解度与淀粉摄入量的回归分析结果表明,RDS降解度随淀粉摄入量的增加呈先升后降的趋势,在淀粉摄入量为5.5 kg/d时达到峰值。这可能是因为当淀粉摄入量较低时,淀粉和干物质摄入量对瘤胃排空速率影响较小,且瘤胃pH稳定,为微生物降解淀粉提供了适宜条件;此时增加淀粉摄入可为微生物生长提供更多底物,从而促进瘤胃发酵。然而,当淀粉摄入量高于5.5 kg/d时,食糜排空速率加快,同时瘤胃pH逐渐降低,最终导致淀粉降解度降低。此外,RES量随淀粉摄入量的增加呈二次曲线上升,该结果进一步证实淀粉摄入量的增加会促进淀粉从瘤胃中的排出速率。
奶牛小肠淀粉消化率的变异较大,为到达十二指肠淀粉流量的40%~80%[2,19,32],本研究中该指标平均值为64.65%。Moharrery等[11]对55项研究数据的综合分析表明,小肠淀粉消化率平均值为60.60%。研究表明,胰腺α-淀粉酶分泌不足是制约反刍动物小肠淀粉消化率的重要因素[33]。从能量利用角度看,淀粉在小肠内消化的能量效率比在瘤胃降解高出约42%,而大肠中淀粉的能量利用效率更低[19,34-35]。因此,只有当小肠淀粉消化率超过70%时,其能量高效利用的优势才能得以体现[36]。但单纯依赖小肠的消化作用,难以弥补瘤胃淀粉降解度不足导致的能量损失。在提高小肠淀粉消化率方面,本团队研究发现,向犊牛[37]和山羊[38]十二指肠灌注亮氨酸可增加胰腺α-淀粉酶的分泌,从而提高小肠淀粉消化率。郭龙等[39]进一步揭示了其分子机制,证实亮氨酸可通过磷脂酰肌醇3-激酶(phosphoinositide 3-kinase,PI3K)/蛋白激酶B(protein kinase B,Akt)-哺乳动物雷帕霉素靶蛋白(mammalian target of rapamycin,mTOR)信号通路促进奶牛胰腺腺泡细胞中淀粉酶的合成和分泌。此外,补充过瘤胃亮氨酸也可提高青年奶牛[40]和奶山羊[41]的小肠淀粉消化率。综上所述,提高瘤胃淀粉降解度或增强小肠淀粉消化能力是实现反刍动物饲粮淀粉高效利用的关键策略。
本研究结果表明,全消化道淀粉消化率与RDS降解度呈线性正相关,而与RES量和RES消化率呈负相关,提示奶牛全消化道淀粉消化率与瘤胃消化的关系比肠道更为密切。瘤胃是淀粉利用的主要部位,小肠难以弥补瘤胃淀粉降解度不足造成的损失。本研究的回归模型再次验证了奶牛肠道淀粉消化能力有限,这可能与胰腺α-淀粉酶分泌不足、小肠上皮细胞葡萄糖转运吸收能力受限以及淀粉在肠腔中滞留时间较短等因素有关[20]。

3.3 奶牛淀粉消化与NDF及氮消化利用的关系

淀粉和NDF是反刍动物饲粮中两大能量来源,二者在瘤胃消化过程中存在显著互作效应,这种互作效应不仅影响养分利用效率,还可能对瘤胃发酵环境和动物生产性能产生深远影响。本研究结果表明,瘤胃NDF降解度与淀粉摄入量及RDS降解量呈线性负相关,淀粉摄入量和RDS降解量每增加1 kg,NDF降解度分别降低2.65和3.11个百分点。已有研究证实,高RDS饲粮可促进淀粉分解菌[如嗜淀粉瘤胃杆菌(Ruminobacter amylophilus)和牛链球菌(Streptococcus bovis)等]增殖,抑制纤维分解菌生长[42]。淀粉分解菌的大量增殖可能与纤维分解菌竞争,优先利用瘤胃中的有限资源(如氮源和生长因子等)并抢占生态位,从而抑制纤维分解菌的活性。陈晓东[43]的研究证实,高RDS饲粮会导致瘤胃纤维降解相关微生物[如普雷沃氏菌科UCG-001(Prevotellaceae UCG-001)、普雷沃氏菌科UCG-003(Prevotellaceae UCG-003)和普雷沃氏菌属(Prevotella)等]的丰度随时间显著降低。此外,淀粉在瘤胃中快速降解会产生大量VFA,导致瘤胃pH降低,抑制纤维分解菌的活性和生长,进而降低NDF的降解效率[5]。为维持瘤胃健康及养分高效利用,饲粮中淀粉与纤维的比例需控制在合理范围。徐明[7]和李飞[8]提出以饲粮peNDF与RDS的比值(CBI)作为评价碳水化合物高效利用与瘤胃健康的指标。CBI更加系统地量化了饲粮中peNDF与RDS含量和比例,能综合反映饲粮碳水化合物结构对瘤胃健康及养分利用效率的影响,为反刍动物饲粮配方优化提供了重要参考。综上所述,淀粉摄入量和RDS降解量的增加可通过改变瘤胃微生物群落结构和降低pH,对NDF消化率产生负面影响。合理调控饲粮中淀粉与纤维的比例,优化CBI,是维持瘤胃健康和养分高效利用的关键策略。
MCP是反刍动物重要的蛋白质来源,主要由瘤胃微生物(包括细菌、原生动物和真菌)合成。RDP和RDS是MCP合成的主要底物和能量来源。本研究结果显示,淀粉摄入量和RDS降解量与瘤胃氮降解量和MCP合成量均呈线性正相关,淀粉摄入量和RDS降解量每增加1 kg,MCP合成量分别增加90和110 g。有研究表明,到达奶牛小肠的微生物氮量与有机物(OM)摄入量呈正相关[44]。作为主要能量来源,淀粉的降解可为瘤胃MCP合成代谢提供能量和碳骨架,促进MCP合成[45]。同时,淀粉降解还可促进细菌增殖,增强瘤胃中蛋白质的利用效率。RDP通过为瘤胃微生物提供氮素和氨基酸,直接促进MCP的合成[46]。此外,饲粮中能氮释放速率同步也是影响MCP合成的重要因素,同时满足瘤胃微生物生长所需的能量和蛋白质,有助于实现MCP合成最大化,并减少能量和氮的浪费[47]。基于原位降解法测定的饲粮OM和氮降解动力学参数建立的瘤胃能氮同步指数表明,25 g N/kg OM降解配比是MCP合成效率最佳比例[48]。同时,RDS/RDP也被认为是反映能氮同步的重要指标[49-50]。综上所述,RDP和RDS在MCP合成中具有协同作用。通过合理调控饲粮中能量和氮的释放速率,优化能氮同步,是提高MCP合成效率和反刍动物生产性能的重要营养策略。

3.4 RDS降解量、饲粮NDF/RDS与奶牛瘤胃发酵的关系

瘤胃发酵产生的VFA是反刍动物的主要能量来源,其中乙酸和丙酸尤为关键。饲粮组成显著影响瘤胃发酵类型:高纤维饲粮促进乙酸型发酵[51-52],而高淀粉饲粮则诱导丙酸型发酵[3,53]。因此,乙丙比是评估瘤胃发酵类型的重要指标。此外,瘤胃pH可反映饲粮产酸能力与瘤胃缓冲能力之间的平衡状态。本研究结果表明,RDS降解量与瘤胃乙丙比及pH呈线性负相关,RDS降解量每增加1 kg,瘤胃乙丙比和pH分别降低0.16和0.06。从代谢机制上看,碳水化合物在瘤胃中先降解为己糖,再经微生物糖酵解生成丙酮酸和还原态[H];丙酮酸可经琥珀酸或丙烯酸途径结合[H]生成丙酸,或通过乙酰辅酶A途径释放[H]合成乙酸、丁酸等[54]。RDS在瘤胃中迅速降解,产生大量[H],改变氧化还原电势[3,55]。积累的[H]可能刺激丙酸生成途径的上调,以消耗[H]来维持氧化还原电势的稳态[56]。同时,淀粉大量降解可促进偏好丙酸型发酵的淀粉利用菌快速增殖[43]。淀粉在瘤胃中快速降解还会导致pH下降,而饲粮中粗纤维(尤其是peNDF)对维持pH稳态具有重要作用[57]。peNDF通过刺激瘤胃机械感受器促进蠕动,增强反刍和咀嚼行为[57]。反刍过程中分泌的唾液富含碳酸氢盐,可有效中和瘤胃酸性物质,维持pH稳定[58]。CBI模型用于量化饲粮peNDF与RDS的关系。然而,本研究中peNDF的数据较少,因此改用NDF/RDS进行回归分析,结果表明,瘤胃pH和乙丙比随NDF/RDS的增加呈二次曲线上升趋势。这一结果与李飞[8]的研究一致,其研究表明瘤胃pH和乙丙比与CBI呈二次曲线关系,随CBI的增加而缓慢上升,进一步印证了CBI在评估瘤胃pH和发酵模式方面的有效性。因此,在高RDS饲粮条件下,建议参考CBI合理调整peNDF比例,以维持健康高效的瘤胃发酵状态。

3.5 RDS降解量、饲粮NDF/RDS与奶牛泌乳性能的关系

RDS降解量是衡量奶牛饲粮中淀粉在瘤胃降解特性的重要指标,可直接影响泌乳性能。RDS通过调控瘤胃发酵模式、能量供应和微生物蛋白合成,显著影响产奶量和乳成分。本研究结果表明,4% FCM产量与RDS降解量呈线性正相关。RDS降解量增加可提高瘤胃丙酸产量[3],而丙酸是肝脏糖异生的主要底物,可为泌乳活动提供能量支持。Shabat等[4]的研究也发现,瘤胃丙酸比例较高的奶牛具有更高的饲料利用效率。本研究中NEL也表现出随RDS降解量增加而线性上升的趋势。然而,有研究表明,当饲粮中淀粉/NDF大于0.72时,4% FCM产量随着淀粉含量的增加而逐渐降低[14],这可能与乳酸过量积累导致瘤胃pH下降及消化功能受损有关[59]。本研究所涉及试验奶牛的瘤胃pH多维持在5.8以上,未出现酸中毒风险,因此,4% FCM产量、NEL与RDS降解量之间均呈线性正相关。而乳脂率与RDS降解量呈线性负相关。RDS降解可促进丙酸型发酵,降低乙丙比,而乙酸是乳脂从头合成的重要前体[6],因此,高RDS饲粮往往会降低奶牛乳脂率。此外,RDS含量过高会抑制瘤胃中溶纤维丁酸弧菌(Butyrivibrio fibrisolvens)和假丁酸弧菌(Pseudobutyrvibrio)的生长,改变脂肪酸氢化途径,生成对乳脂合成具有抑制作用的反-10,顺-12共轭亚油酸[60]。综上所述,RDS对奶牛泌乳性能的影响具有双重性:一方面,通过促进能量供应提高产奶量;另一方面,如果RDS含量过高,可能改变瘤胃发酵模式和脂肪酸代谢途径抑制乳脂合成。因此,合理调控饲粮中RDS含量及其与NDF的比例,是优化奶牛泌乳性能的关键策略。
本研究进一步分析饲粮NDF/RDS对泌乳性能的影响,结果表明,饲粮NDF/RDS与4% FCM产量呈线性负相关,该趋势与RDS对4% FCM产量的影响相反,推测其原因可能是淀粉降解量减少导致泌乳所需能量供应不足;而饲粮NDF/RDS与乳脂率之间存在二次曲线关系——随着饲粮NDF/RDS的升高,乳脂率呈现先上升后下降的变化趋势,这一结果与瘤胃液中乙丙比随饲粮NDF/RDS升高的变化规律一致。随着饲粮NDF/RDS的升高,更多的纤维在瘤胃中降解,生成足够的乙酸用于合成乳脂,有效抵消RDS对乳脂率的负面影响[61]。该结论与李飞[8]的研究结果相符,其研究同样发现乳脂率与CBI(peNDF/RDS)呈二次曲线关系,且建议将CBI控制在0.93~1.30,以维持瘤胃高效健康状态(乳脂率>3.5%,瘤胃液乙丙比2.2~3.0)。本研究推荐饲粮NDF/RDS应>1.48,以维持瘤胃高效健康状态。上述结果表明,通过合理调控饲粮碳水化合物结构,不仅可优化瘤胃发酵模式,还能有效平衡奶牛乳脂率与产奶量,为奶牛高效生产提供科学参考。
需注意的是,本研究纳入的文献中,所有试验奶牛均安装了瘤胃与十二指肠瘘管以测定饲粮RDS含量,且试验牛平均标准乳产量为28.38 kg/d(属中产奶牛水平)。因此,本研究得出的结论是否适用于高产奶牛,仍需后续研究进一步验证。

4 结论

本研究通过Meta分析表明,谷物种类和加工方式显著影响饲粮淀粉消化率;RDS降解量的增加可通过促进瘤胃丙酸型发酵,提升4% FCM产量,但过量时会抑制纤维降解及降低乳脂率。通过调控饲粮RDS的降解特性、优化饲粮碳水化合物结构,能够有效平衡瘤胃pH稳态与乳脂合成效率。

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