Chinese Journal of Animal Nutrition >

2025 , Vol. 37 >Issue 7: 4889 - 4900

DOI: https://doi.org/10.12418/CJAN2025.399

RESEARCH PAPER

Evaluating Nutritional Values of Three Kinds of Roughages Based on Ruminant Feeding System of INRA (2018)

  • ZHANG Xiaojing ,
  • XIE Changlin ,
  • ZHUANG Su ,
  • LIU Qiang , *
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  • College of Animal Science and Technology, Nanjing Agricultural University, Nanjing 210095, China
* associate professor, E-mail:

Received date: 2024-12-13

  Online published: 2025-07-12

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Abstract

This experiment was conducted to evaluate the nutritional values of three kinds of roughages based on the ruminant feeding system of INRA (2018), and provide basic data for the evaluation and utilization of crop straw feed resources. In the experiment, three semi-purified diets with similar energy and crude protein (CP) content were formulated using one of the three roughages, which were wheat straw, peanut vine and Leymus chinensis, as the sole fiber source, respectively. Nine Boer crossbred male goats with similar body weight of (70.0±2.5) kg and good body condition were selected and the T-shaped abomasum fistulas were installed through surgery. Using a 3×3 repeated Latin formula experimental design, the goats and diets were allocated for a total of 3 feeding cycle experiments, each lasting 18 days, including a 15-day pre-trial period and a 3-day formal trial period. During the formal trial period, the abomasum digesta and fecal samples of the goats were collected every day to determine the rumen degradability (RD) and apparent total tract digestibility (ATTD) of nutrients, and the synthesis amount of rumen microbial protein (MCP). And according to the relevant parameters and formulas of INRA (2018) system, the nutritional parameters such as RD, ATTD, protein digestible in intestine (PDI), protein digestible in intestine supplied by rumen undegradable protein (RUP) (PDIA), protein digestible in intestine supplied by MCP (PDIM) and rumen protein balance (RPB) corresponding to the nutrients of the three kinds of roughages were calculated. The results showed as follows: 1) there were significant differences in RD and ATTD of nutrients among the three semi-purified diets (P<0.05). Among them, the RD and ATTD of dry matter (DM), organic matter (OM) and gross energy (GE) in wheat straw diet were the lowest, and significantly lower than those in the other two diets (P<0.05); the ATTD of neutral detergent fiber (NDF) and acid detergent fiber (ADF) in peanut vine diet and Leymus chinensis diet was significantly higher than that in wheat straw diet (P<0.05). 2) The RD and ATTD of CP in Leymus chinensis diet were significantly higher than those in wheat straw diet (P<0.05). There were no significant differences in RUP intestinal digestibility and MCP intestinal digestibility, as well as the contents of PDIA and PDI among the three semi-purified diet groups (P>0.05). The PDIM content in wheat straw diet group and peanut vine diet group was significantly higher than that in Leymus chinensis diet group (P<0.05), and the RPB values in the three roughage diet groups were all minus. 3) The organic matter digestibility (OMd), dry matter digestibility (DMD) and nitrogen effective degradability in rumen of peanut vine were all the highest, while those of wheat straw were relatively low. The digestible energy (DE), PDIA content and RPB value of Leymus chinensis were the highest, while those of wheat straw were the lowest. The PDI content of peanut vine was the highest, followed by wheat straw, and Leymus chinensis was the lowest. 4) The numerical trends of OMd, energy digestibility (Ed), DE, and voluntary dry matter intake of sheep (VDMIm) of the three kinds of roughages calculated based on model 2 in INRA (2018) and the substitution method with semi-purified diet were basically consistent, but they were significantly different from the results obtained using model 1 in INRA (2018). In conclusion, the fiber components in Leymus chinensis and peanut vine are more easily degraded than those in wheat straw. Therefore, their DMD, OMd and DE are significantly higher than those in wheat straw. In INRA (2018) system, the RPB values of the three kinds of roughages are all minus, indicating that the nitrogen provided by the rumen degradable protein is insufficient to meet the requirements for the synthesis of MCP through rumen degradation (or fermentation) of the feed OM. The predicted values of model 2 in INRA (2018) system for the nutritional parameters of the three kinds of roughages are close to the calculated values by substitution in vivo of this experiment. However, the accuracy of some models and their application scope still need more exploration.

Key words： roughages; semi-purified diets; nutrient values; goats; INRA (2018)

Cite this article

ZHANG Xiaojing , XIE Changlin , ZHUANG Su , LIU Qiang . Evaluating Nutritional Values of Three Kinds of Roughages Based on Ruminant Feeding System of INRA (2018)[J]. Chinese Journal of Animal Nutrition, 2025 , 37(7) : 4889 -4900 . DOI: 10.12418/CJAN2025.399

据估计,我国每年约产10亿t各类农作物秸秆[1]。尽管秸秆存在直接还田、用作造纸和建材等多种利用途径,但作为饲用料始终是其最有潜力的生态可持续利用方式。秸秆饲用既可以缓解我国草食动物粗饲料供应不足,又可以转变为有机粪肥,提高土壤肥力和农作物产量,保障农业生态系统良性循环[2]。秸秆普遍纤维含量高、质地粗硬、适口性差,养分含量和消化利用率变化较大,客观评价其营养价值对合理利用秸秆饲料资源具有重要的参考价值和经济意义。反刍动物饲料营养价值评定经历了从早期基于单室模型的代谢能-可消化粗蛋白质体系[ARC(1980)][3],到能反映饲料蛋白质在瘤胃和小肠内不同消化机制(二室模型)的代谢能-瘤胃可降解蛋白质和过瘤胃蛋白体系[AFRC(1993)][4],再到净能-小肠可消化蛋白质或可吸收氨基酸表达体系[NRC(2001)和INRA(2018)]的进化[5-6]。其中,INRA(2018)是法国农业科学院在其原有的瘤胃降解模型基础上,引入NRC(2001)的可代谢蛋白概念,用以区分各种饲料原料的瘤胃未降解蛋白质(rumen undegradable protein,RUP)和瘤胃合成的微生物蛋白(microbial protein,MCP),并分别根据二者的肠道消化率推算得出肠道可消化蛋白质(protein digestible in intestine,PDI)总量,即PDI=RUP提供的肠道可消化蛋白质(PDIA)+MCP提供的肠道可消化蛋白质(PDIM);同时,通过评价各种饲料原料的潜在瘤胃蛋白质平衡(rumen protein balance,RPB)值,保障饲喂后的瘤胃氮能平衡,从而优化瘤胃MCP的合成效率;通过基于干物质自由采食量(voluntary dry matter intake,VDMI)的各种原料的填充值(fill value),保障实际生产中饲粮供应量与动物采食能力之间的匹配。优化后的参数和模型为实现反刍动物养分高效利用和饲粮配制提供了可行性依据[6],具有较高的实用性。研究表明,INRA(2018)体系在有机物(OM)和中性洗涤纤维(NDF)消化率预测方面,比NRC(2001)体系更接近实际情况[7]。因此,本文以INRA(2018)体系的模型参数为基础,尝试评估试验选用粗饲料的主要营养价值参数,供同行参考。为避免已有同类研究多采用多种纤维来源原料组成的混合饲粮对待测粗饲料养分降解和消化率测定的干扰,本试验采用由单一粗饲料组成的半纯合饲粮,试图通过观测真胃食糜和粪便中饲粮养分的变化,探讨不同粗饲料的养分在试验羊瘤胃和全消化道内的利用状况。在半纯合饲粮养分的体内消化试验结果基础上,借鉴INRA(2018)的相关模型和套算法推算小麦秸秆、花生秧和羊草3种粗饲料的主要营养价值参数,既检验INRA(2018)模型的可行性,又为所测试秸秆的饲料化利用提供基础数据。

1 材料与方法

1.1 试验设计与饲粮

本试验经南京农业大学实验动物福利与伦理委员会审批,批准编号:NJAU.No20230403040。试验选用9只体重为(70.0±2.5) kg的健康杂交肉用波尔公山羊,手术安装真胃T型瘘管,按照Kim等[8]的3×3无偏有重复拉丁方设计分配试验饲粮和动物轮换,试验分3期,每期每种饲粮饲喂3只试验羊,包括预试期15 d,正试期3 d。
试验采用单因素3水平试验设计,分别选用机械收获后,在田间自然晒干、打捆的小麦秸和花生秧,以及7月中旬机械收割、自然晒干的第3茬羊草作为唯一粗饲料来源,辅以少量鱼粉、玉米淀粉和营养性添加剂,参照《肉羊营养需要量》(NY/T 816—2021)肉用山羊推荐营养水平配制能量和粗蛋白质(CP)含量相近的3种半纯合全价试验饲粮,饲粮组成及营养水平见表1。每种饲粮中分别加入用同种纤维原料制作的铬标记纤维(制备方法参照Ramanzin等[9]),用于消化率计算。所有饲粮均用平磨颗粒机(葛力牌YL 112 M-4型,粒径=6 mm)制粒。
表1 饲粮组成及营养水平

Table 1 Composition and nutrient levels of diets

项目
Items		 小麦秸饲粮
Wheat straw diet		 花生秧饲粮
Peanut vine diet		 羊草饲粮
Leymus chinensis diet
原料(风干基础) Ingredients (air-day basis)/(g/kg)
小麦秸 Wheat straw 624.7
花生秧 Peanut vine 685.8
羊草 Leymus chinensis 673.8
铬标记纤维 Chromium-labeled fibers 0.3 0.2 0.2
玉米淀粉 Corn starch 156.2 121.1 168.5
鱼粉 Fish meal 164.1 153.3 84.2
尿素 Urea 3.9 11.8
植物油 Vegetable oil 15.6 12.6
石灰石 Limestone 8.4
磷酸钙 Ca3(PO4)2 9.4 16.1 16.9
碳酸氢钠 NaHCO3 11.7 12.1 8.4
氧化镁 MgO 6.2 6.5 6.7
氯化钠 NaCl 7.8 4.8 8.4
维生素预混料 Vitamin premix1) 0.1 0.1 0.1
合计 Total 1 000.0 1 000.0 1 000.0
营养水平 Nutrient levels2)
干物质 DM/(g/kg) 975.6 968.0 973.0
有机物 OM/(g/kg DM) 847.8 849.7 890.8
总能 GE/(MJ/kg DM) 16.4 16.7 18.5
消化能 DE/(MJ/kg DM) 11.2 13.5 13.9
粗灰分 Ash/(g/kg DM) 152.2 150.3 109.2
粗蛋白质 CP/(g/kg DM) 130.3 121.1 106.4
钙 Ca/(g/kg DM) 0.1 0.1 0.1
磷 P/(g/kg DM) 0.3 0.3 0.3
铬(以三氧化二铬计) Cr (as Cr2O3)/(g/kg DM) 0.1 0.1 0.1
粗纤维 CF/(g/kg DM) 220.9 244.8 273.2
中性洗涤纤维 NDF/(g/kg DM) 423.5 364.7 500.3
酸性洗涤纤维 ADF/(g/kg DM) 244.8 269.2 298.2
酸性洗涤木质素 ADL/(g/kg DM) 24.5 73.7 75.4

1)维生素预混料为每千克饲粮提供 The premix provided the following per kg of diets:VA 3 800 IU,VD3 1 150 IU,VE 10 IU,生物素 biotin 0.02 mg,烟酰胺 nicotinamide 15 mg。
2)消化能为计算值[10],其余为实测值。DE was a calculated value[10], while the others were measured values.

1.2 瘘管安装与饲养管理

试验羊饲养于南京农业大学动物科技学院动物房,T型真胃瘘管(聚乙烯材质,管体8 cm,内径2 cm)购自武汉科立博牧业科技有限公司。为了研究饲粮养分瘤胃降解平衡后的利用情况,瘘管安装在真胃背囊侧,安装手术由南京农业大学兽医院外科邓益峰教授团队协助完成。术后试验羊单笼饲养于配备漏缝地板的镀锌钢管代谢笼内,恢复14 d,直至创口愈合。试验期间参照60 g DM/kg BW0.75标准每天定量饲喂1.40~1.50 kg饲粮,每日08:00和20:00等量饲喂2次,自由饮水。羊舍温度控制在22~25 ℃,相对湿度为40%~60%,保持室内通风和羊舍卫生。

1.3 样品采集

正试期每天10:00、14:00和18:00分别采集每只试验羊的真胃食糜和粪便样品,真胃食糜采样时,每次弃去前期流出的10~20 g食糜,再连续收集80~100 g新鲜食糜。每次采集的食糜和粪便样品临时保存在4 ℃冰箱,每天采样结束后,按羊只编号将3个时间点的样品等重量混合,迅速置于-20 ℃冰箱冷冻保存。每期采样结束后,分别将每只羊每天的真胃食糜和粪便样品室温消融,再按天等重量混合合并为1个分析样品,立即取部分混合鲜样用于MCP和氨态氮(NH3-N)含量检测,剩余样品65 ℃烘干,室温回潮24 h,粉碎过40目筛,于-20 ℃冰箱保存备用。

1.4 测定指标及方法

1.4.1 常规养分

饲粮、粪便及真胃食糜样品中干物质(DM)、粗灰分(Ash)和铬(Cr)含量分别参照GB/T 6435—2014、GB/T 6438—2007和GB/T 13088—2006中方法进行测定,OM含量=DM含量-Ash含量;饲粮中钙(Ca)和磷(P)参照NY/T 3318—2018中方法进行测定;CP含量参照GB/T 6432—2018中方法,采用全自动凯氏定氮仪(FOSS,丹麦)进行测定;总能(GE)采用全自动量热仪(TYHW-V,鹤壁市天宇仪器仪表制造有限公司)进行测定。

1.4.2 纤维成分

饲粮、粪便及真胃食糜样品中粗纤维(CF)、NDF、酸性洗涤纤维(ADF)和酸性洗涤木质素(ADL)含量参照Van Soest等[11]的方法,采用纤维自动分析仪(ANKOM-200i,美国)进行测定。

1.4.3 MCP和NH3-N含量

粪便及真胃食糜样品中MCP含量参照Zinn等[12]的嘌呤碱基法进行测定;NH3-N含量参照冯宗慈等[13]的方法,采用分光光度计(METASH UV 8000A,上海元析仪器有限公司)进行测定。

1.5 指标计算

1.5.1 饲粮养分瘤胃降解率(rumen degradability,RD)和全消化道表观消化率(apparent total tract digestibility,ATTD)

本研究以真胃食糜中饲粮养分的变化作为衡量其RD的指标,相关养分的RD和ATTD按常规指示剂法计算,计算公式如下:
RD(%)=[1-(饲粮DM中Cr含量×真胃食糜DM中养分含量)/(饲粮DM中养分含量×真胃食糜DM中Cr含量)]×100。
ATTD(%)=[1-(饲粮DM中Cr含量×粪便DM中养分含量)/(饲粮DM中养分含量×粪便DM中Cr含量)]×100。

1.5.2 INRA(2018)反刍动物饲喂体系评价饲粮营养参数

根据INRA(2018)反刍动物饲喂体系模型对饲粮营养参数进行推算,计算公式如下:
真胃食糜中RUP含量(g/kg DM)=[饲粮中CP含量×(1-饲粮中CP的RD)]/(1-饲粮中DM的RD)-真胃食糜中MCP含量-真胃食糜中NH3-N含量×6.25-14.2×(真胃食糜中Cr含量/饲粮中Cr含量);
粪便中未降解蛋白质(undegradable protein,UDP)含量(g/kg DM)=[饲粮中CP含量×(1-饲粮中CP的ATTD)]/(1-饲粮中DM的ATTD)-粪便中MCP含量-粪便中NH3-N含量×6.25-4.49×(粪便中Cr含量/饲粮中Cr含量);
式中:14.2和4.49分别为瘤胃和肠道内源氮分泌量(g/kg DMI)[10]。
RUP肠道消化率(%)=[1-(真胃食糜DM中Cr含量×粪便DM中UDP含量)/(真胃食糜DM中RUP含量×粪便DM中Cr含量)]×100;
MCP肠道消化率(%)=[1-(真胃食糜DM中Cr含量×粪便DM中MCP含量)/(真胃食糜DM中MCP含量×粪便DM中Cr含量)]×100;
PDIA(g/kg DM)=真胃食糜中RUP含量×RUP的肠道消化率;
PDIM(g/kg DM)=真胃食糜中MCP含量×MCP的肠道消化率;
PDI(g/kg DM)=PDIA+PDIM;
RPB(g/kg DM)=饲粮中CP含量×饲粮中CP的RD-PDIM/MCP的肠道消化率/0.8-14.2。
式中:0.8为MCP中真蛋白质的比例,14.2为瘤胃内源氮分泌量(g/kg DM)[10]。

1.5.3 套算法推算待测粗饲料营养参数

为平衡半纯合饲粮的氮能含量,本试验在待测饲粮中加入一定量的鱼粉、淀粉、植物油及尿素等辅助原料,计算过程中辅助原料养分的消化参数均统一参照Baumont等[10]和INRAE-CIRAD-AFZ饲料营养价值表[14]中的相关数据。采用套算法[15]计算待测粗饲料养分的RD或ATTD,计算公式如下:
NDi(%)=100×(NR×d-(Nij×Cj×dNj)/(Ci×Ic)。
式中:NDi为待测粗饲料i中养分N的RD或ATTD;NR为饲粮中养分N的含量(g/kg DM);d为饲粮中养分N的RD或ATTD;Nij为平衡料j中养分N的含量(g/kg DM);j为鱼粉、淀粉、植物油、尿素或其他添加剂之一;Cj为饲粮中平衡料j的用量百分比;dNj为平衡料j中养分N的RD或ATTD;Ci为饲粮中待测粗饲料的用量百分比;Ic中待测粗饲料中养分N的含量(g/kg DM)。

1.5.4 INRA(2018)模型预测待测粗饲料部分营养参数

根据INRA(2018)模型预测待测粗饲料的部分营养参数,相关计算如下。
模型1,根据养分组成计算粗饲料有机物消化率(organic matter digestibility,OMd),计算公式如下:
羊草或小麦秸(禾本科干草)OMd(%)=104.9-0.127×ADF+0.014×CP;
花生秧(豆科干草)OMd(%)=98.5-0.114×ADF。
模型2,根据NDF的ATTD计算3种粗饲料OMd,计算公式如下:
OMd(%)=[785-NDF×(1-NDF ATTD/100)]/8.62。
式中:NDF是粗饲料中NDF含量(g/kg DM)。
能量消化率(energy digestibility,Ed)计算公式如下:
小麦秸(秸秆)Ed(%)=-2.949+0.985×OMd;
花生秧(脱水豆科牧草)Ed(%)=-3.0+1.003×OMd;
羊草(禾本科干草)Ed(%)=-2.556+0.985×OMd;
消化能代谢率(%)=[86.38-0.099×(CF/OM)-0.196×(CP/OM)]/100。
式中:CF、CP、OM和ADF含量单位均为g/kg DM。
绵羊干物质自由采食量(VDMIm,g DM/kgBW0.75)=11.8+0.432×OMd+0.1×CP+ 1m+2m。
式中:小麦秸和羊草的校正因子 1m均为-0.8, 2m分别为0和2.9;花生秧的校正因子 1m和 2m分别为9.4和0。

1.6 数据分析与统计

试验数据经Excel 2019整理后,采用SPSS 26.0软件一般线性模型进行单变量方差分析,固定因子为饲粮种类,随机因子为羊只编号和试验轮次编号,组间差异采用S-N-K法进行比较,结果数据采用平均值和均值标准误(SEM)表示,P<0.05为差异显著。

2 结果

2.1 3种半纯合饲粮养分RD和ATTD

由表2可知,3种半纯合饲粮间各养分的RD和ATTD均存在显著差异(P<0.05)。总体而言,小麦秸饲粮常规养分(DM、OM、Ash和GE)的RD和ATTD均最低,显著低于其他2种饲粮(P<0.05)。花生秧饲粮DM、OM和GE的ATTD最高(P<0.05),显著高于其他2种饲粮(P<0.05);而羊草饲粮Ash的ATTD最高,显著高于其他2种饲粮(P<0.05)。就纤维成分而言,羊草饲粮和小麦秸饲粮NDF和ADF的RD均显著高于花生秧饲粮(P<0.05);而羊草饲粮ADL的RD最高,显著高于其他2种饲粮(P<0.05);同时,花生秧饲粮和羊草饲粮NDF和ADF的ATTD显著高于小麦秸饲粮(P<0.05),且花生秧饲粮ADL的ATTD显著高于小麦秸饲粮和羊草饲粮(P<0.05)。
表2 3种半纯合饲粮养分RD和ATTD

Table 2 RD and ATTD of nutrients in three semi-purified diets%

项目
Items		 小麦秸饲粮
Wheat straw diet		 花生秧饲粮
Peanut vine diet		 羊草饲粮
Leymus chinensis diet		 均值标准误
SEM		 P值
P-value
瘤胃降解率 RD
干物质 DM 55.08b 61.69a 65.33a 1.961 0.008
有机物 OM 55.59b 61.72a 64.42a 1.991 0.021
粗灰分 Ash 24.22b 45.13a 45.11a 3.561 <0.001
总能 GE 52.74b 59.75a 65.48a 2.205 0.004
中性洗涤纤维 NDF 53.41a 44.12b 56.80a 2.849 0.019
酸性洗涤纤维 ADF 52.93a 43.66b 55.05a 2.750 0.025
酸性洗涤木质素 ADL 26.84b 36.22b 50.47a 3.967 0.003
全消化道表观消化率 ATTD
干物质 DM 68.82c 79.88a 75.36b 0.983 <0.001
有机物 OM 71.61c 82.70a 75.28b 0.869 <0.001
粗灰分 Ash 44.42c 58.24b 65.31a 1.931 <0.001
总能 GE 68.25c 80.94a 74.96b 1.041 <0.001
中性洗涤纤维 NDF 57.39b 68.85a 65.25a 1.349 <0.001
酸性洗涤纤维 ADF 56.80c 69.47a 65.40b 1.316 <0.001
酸性洗涤木质素 ADL 36.93b 65.58a 61.50b 1.333 <0.001

同行数据肩标相同字母或无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同。

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

2.2 3种半纯合饲粮对山羊蛋白质消化参数的影响

由表3可知,3种半纯合饲粮对山羊CP的RD和ATTD以及RUP、UDP、MCP、NH3-N含量存在差异显著(P<0.05)。小麦秸饲粮组真胃食糜中MCP含量最高,显著高于羊草饲粮组(P<0.05);而花生秧饲粮组粪便中MCP含量最高,显著高于其他2组(P<0.05)。羊草饲粮CP的RD和ATTD均显著高于小麦秸饲粮(P<0.05)。对于真胃食糜中RUP含量以及粪便中UDP含量,花生秧饲粮组最高,羊草饲粮组最低;而对于真胃食糜和粪便中NH3-N含量,小麦秸饲粮组最高,羊草饲粮组最低。3种半纯合饲粮组之间RUP肠道消化率和MCP肠道消化率以及PDIA和PDI含量均差异不显著(P>0.05),而PDIM含量和RPB值存在显著差异(P<0.05)。小麦秸饲粮组和花生秧饲粮组PDIM含量显著高于羊草饲粮组(P<0.05);而羊草饲粮组RPB值最高,显著高于其他2组(P<0.05)。
表3 3种半纯合饲粮对山羊蛋白质消化参数的影响

Table 3 Effects of three semi-purified diets on protein digestion parameters of goats

项目
Items		 小麦秸饲粮
Wheat straw
diet		 花生秧饲粮
Peanut vine
diet		 羊草饲粮
Leymus
chinensis diet		 均值标准误
SEM		 P值
P-value
真胃食糜 Abomasum digesta
粗蛋白质瘤胃降解率 RD of CP/% 39.39b 40.78b 59.85a 2.728 <0.001
瘤胃未降解蛋白质 RUP/(g/kg DM) 69.89a 80.41a 34.33b 5.759 0.001
微生物蛋白 MCP/(g/kg DM) 75.77a 66.44a 50.63b 4.791 0.008
氨态氮 NH3-N/(g/kg DM) 1.40a 0.66b 0.93b 0.090 <0.001
全消化道 Total digestive tract
粗蛋白质全消化道表观消化率
ATTD of CP/%		 78.56b 80.55a 83.13a 0.756 0.003
粪便中未降解蛋白质 UDP in feces/(g/kg DM) 57.61b 79.98a 40.19c 3.598 <0.001
粪便中微生物蛋白 MCP in feces/(g/kg DM) 4.94b 8.40a 4.41b 0.357 <0.001
粪便中氨态氮 NH3-N in feces/(g/kg DM) 0.05a 0.04ab 0.004b 0.004 0.031
肠道 Intestinal tract
瘤胃未降解蛋白质肠道消化率
Intestinal digestibility of RUP/%		 43.73 46.18 66.73 4.418 0.323
微生物蛋白肠道消化率
Intestinal digestibility of MCP/%		 95.13 93.37 93.42 0.422 0.153
瘤胃未降解蛋白质提供的肠道可消化蛋白质
PDIA/(g/kg DM)		 31.69 45.16 36.01 5.520 0.539
微生物蛋白提供的肠道可消化蛋白质
PDIM/(g/kg DM)		 66.00a 62.15a 47.61b 2.869 0.016
肠道可消化蛋白质 PDI/(g/kg DM) 97.69 104.87 71.69 5.634 0.242
瘤胃蛋白质平衡 RPB/(g/kg DM) -49.47b -47.87b -13.80a 4.879 0.001

2.3 3种粗饲料主要营养参数

由表4可知,3种粗饲料DM含量相近;羊草OM含量高于花生秧和小麦秸;小麦秸和花生秧Ash含量高于羊草;花生秧和羊草CP含量高于小麦秸;羊草GE高于小麦秸和花生秧;羊草NDF和ADF含量高于小麦秸和花生秧;花生秧和羊草ADL含量高于小麦秸。3种粗饲料营养参数推算结果中,花生秧OMd、干物质消化率(DMD)和氮瘤胃有效降解率均最高,小麦秸较低;而羊草消化能(DE)、PDIA含量和RPB值最高,小麦秸最低;花生秧PDI含量最高,小麦秸次之,羊草最低。
表4 3种粗饲料主要营养参数

Table 4 Main nutritional parameters of three kinds of roughages

项目
Items		 小麦秸
Wheat straw		 花生秧
Peanut vine		 羊草
Leymus chinensis
营养成分 Nutrients
干物质 DM/(g/kg) 938.25±1.41 969.73±2.49 980.02±1.96
有机物 OM/(g/kg DM) 879.45±5.37 868.66±0.54 929.87±0.02
粗灰分 Ash/(g/kg DM) 120.55±5.37 131.34±0.54 70.13±0.02
总能 GE/(MJ/kg DM) 16.87±0.02 16.39±0.04 18.52±0.14
粗蛋白质 CP/(g/kg DM) 26.60±0.37 69.55±0.24 78.84±0.00
粗纤维 CF/(g/kg DM) 364.81±0.86 365.64±5.48 414.77±1.20
中性洗涤纤维 NDF/(g/kg DM) 677.52±2.11 531.53±6.02 742.40±4.44
酸性洗涤纤维 ADF/(g/kg DM) 391.65±0.88 392.49±5.59 442.63±1.96
酸性洗涤木质素 ADL/(g/kg DM) 39.17±0.12 107.39±0.67 111.94±3.53
推算参数 Parameters prediction
有机物消化率 OMd/% 56.21 78.04 66.52
干物质消化率 DMD/% 84.53 94.09 88.27
消化能 DE/(MJ/kg DM) 9.20 13.63 14.11
氮瘤胃有效降解率 Effective degradability of nitrogen in rumen/% 30.06 33.08 26.61
瘤胃未降解蛋白质提供的肠道可消化蛋白质 PDIA/(g/kg) -21.12 3.75 18.00
肠道可消化蛋白质 PDI/(g/kg) 57.43 69.44 50.02
瘤胃蛋白质平衡 RPB/(g/kg) -131.79 -103.78 -70.93

2.4 3种粗饲料营养参数的INRA(2018)模型预测值和体内试验套算值比较

由表5可知,3种粗饲料的消化能代谢率差异不明显。根据模型2和半纯合饲粮套算法计算的3种粗饲料OMd、Ed、DE和VDMIm数值趋势基本一致,花生秧和羊草均高于小麦秸,但与利用模型1所得结果差异明显。其中,3种算法所得的小麦秸OMd接近(55.54%~57.58%),但羊草(61.14%~66.52% vs 49.77%)和花生秧(71.86%~78.04% vs 53.76%)OMd的预测值相差较大,而且利用模型1预测得到的羊草和花生秧OMd反而低于小麦秸。
表5 3种粗饲料营养参数的INRA(2018)模型预测值和体内试验套算值比较

Table 5 Comparison of predicted values by INRA (2018) model and values calculated from in vivo experiment for nutritional parameters of three kings of roughages

项目
Items		 方法
Methods		 小麦秸
Wheat straw		 花生秧
Peanut vine		 羊草
Leymus
chinensis




有机物消化率
OMd/%		 体内试验套算值 Calculated value by substitution in vivo 56.21 78.04 66.52
模型1预测值 Predicted value in model 1 55.54 53.76 49.77
模型2预测值 Predicted value in model 2 57.58 71.86 61.14




能量消化率
Ed/%		 体内试验套算值 Calculated value by substitution in vivo 54.52 83.18 76.19
模型1预测值 Predicted value in model 1 52.15 50.00 46.92
模型2预测值 Predicted value in model 2 53.76 69.08 57.67




消化能
DE/(MJ/kg DM)		 体内试验套算值 Calculated value by substitution in vivo 9.20 13.63 14.11
模型1预测值 Predicted value in model 1 8.55 8.35 8.68
模型2预测值 Predicted value in model 2 9.07 11.32 10.68
消化能代谢率
Metabolic rate of DE/%		 预测值 Predicted value 86.33 86.32 86.32


绵羊干物质自由采食量
VDMIm/(g DM/kg BW0.75)		 体内试验套算值 Calculated value by substitution 37.94 43.07 50.36
模型1预测值 Predicted value in model 1 37.65 32.58 43.12
模型2预测值 Predicted value in model 2 38.53 40.40 45.13

3 讨论

3.1 3种半纯合饲粮养分瘤胃降解情况

饲粮养分整体降解和消化可视作其中原料养分降解和消化的加和。本试验中,尽管3个半纯合饲粮中,粗饲料均占了很高的比例(62%~68%),但为了平衡饲粮GE和CP含量而加入的鱼粉和淀粉对饲粮相关养分降解率和消化率的测定不可避免地会产生影响,而且可能影响还很大,因为其对饲粮中个别养分含量的贡献较大。就瘤胃降解阶段而言,羊草饲粮反映出较高的DM、OM、GE和纤维成分降解率,这与袁翠林等[16]的研究结果趋势(花生秧>羊草)略有不同。这可能部分归因于羊草饲粮中淀粉添加量较高,而玉米淀粉在反刍动物瘤胃内的降解率普遍较高,接近70%[17];也可能与羊草中可溶性成分较多,非淀粉多糖木质化程度较低,易降解有关[18]。花生秧饲粮DM和OM的RD显著高于小麦秸饲粮,而纤维成分的RD显著低于小麦秸饲粮,说明花生秧纤维在瘤胃中比小麦秸纤维更难降解或降解速度更慢。从ATTD来看,花生秧饲粮DM、OM和GE的ATTD均显著高于鱼粉和淀粉用量相近的小麦秸饲粮,同时其纤维成分的ATTD也高于小麦秸饲粮,由此可知纤维成分后肠降解率的提高是导致上述效果的主要原因,该结果与李春雷[19]的研究结果一致。同理,羊草饲粮纤维成分的ATTD高于小麦秸饲粮饲粮,这也是其DM、OM和GE的ATTD高于小麦秸饲粮的主要原因。综合3种饲粮纤维成分的RD和ATTD变化可知,花生秧饲粮纤维成分的RD最低,而ATTD最高,这可能与豆科植物纤维中甲酯化果胶含量较高,而去甲酯化是果胶多糖降解的前提条件和限速环节[20]。因此可以推测,较慢的去甲酯化速度是限制花生秧纤维在瘤胃中降解的主要原因,而去甲酯化后的花生秧纤维在后肠较易降解,以NDF的ATTD和RD差值为例,花生秧饲粮为24.73个百分点,羊草饲粮为8.45个百分点,小麦秸饲粮为3.98个百分点,从而使花生秧饲粮纤维成分表现出最高的ATTD。尽管羊草和小麦秸均属禾本科植物,但羊草饲粮NDF和ADF的RD和ATTD均高于小麦秸饲粮,而且其对应成分的ATTD与RD差值也高于小麦秸饲粮,这可理解为小麦秸纤维化程度高,经瘤胃降解后,后肠较难进一步降解,而羊草纤维在后肠二次发酵过程中仍有较高的降解率。

3.2 3种半纯合饲粮对山羊蛋白质消化的影响

虽然为了平衡待测粗饲料CP含量的差异,但饲粮中加入的鱼粉和尿素对粗饲料CP的降解率和消化率测定仍产生了不可避免的影响。例如,本试验中羊草饲粮CP的RD显著高于其他2种饲粮,这就不能排除其中加入的尿素的影响。另外,羊草饲粮的纤维成分含量高于其他2种饲粮,可能延长饲粮的瘤胃滞留时间,进而提高其CP的RD。同理,小麦秸饲粮CP的RD也应包含尿素降解的部分,但其值仍与花生秧饲粮接近,说明小麦秸本身CP的RD低于花生秧,因为后者饲粮未添加尿素。此外,小麦秸饲粮CP含量高于花生秧饲粮(130.3 g/kg DM vs 121.1 g/kg DM),但前者真胃食糜中RUP含量反而低于后者(69.89 g/kg DM vs 80.41 g/kg DM)也支持上述观点。3种饲粮RPB值均为负值(-49.47 g/kg DM~-13.80 g/kg DM),这说明相对MCP合成所需而言,饲粮CP瘤胃降解供应的NH3-N不足,也说明3种粗饲料CP的RD均较低,可能限制了MCP的合成。此外,本试验所配制的3种饲粮CP含量偏低也可能是影响MCP合成量的重要原因,因为3种饲粮的CP含量与其真胃食糜MCP含量高低顺序一致。就全消化道而言,羊草饲粮和花生秧饲粮CP的ATTD显著高于小麦秸饲粮,相应的羊草饲粮RUP肠道消化率(66.73%)也明显高于其他2种饲粮,说明羊草饲粮的RUP比花生秧饲粮的RUP在后肠中更易消化,而小麦秸饲粮的RUP在后肠最难消化(ATTD为43.73%),该结果与王慧娟[21]利用小尾寒羊体内试验得到的瘤胃未降解残渣CP的小肠消化率结果(小麦秸34.79%,羊草40.59%,地瓜秧37.14%)一致。3种饲粮MCP肠道消化率基本相同(93.37%~95.13%),但明显高于Raisanen[22]报道(80%),这可能与本试验采用限制饲喂和饲粮中CP含量偏低有关,也与PDI中PDIM占比较高(59.26%~67.56%)的结果吻合。

3.3 3种粗饲料营养价值分析

从本试验选用的3种粗饲料的营养参数测定结果来看,绝大部分指标的测定值与同类原料的报道值[23-25]接近,仅羊草CF和NDF含量测定值高于中国饲料数据库的CF(34%)和NDF(67%)含量,这可能是由于试验用羊草来自生长晚期的样品,木质化程度较高[26]。本试验利用套算法所得的羊草OMd、DMD和DE与赵浩翔等[27]利用体外三步法测定的绒山羊对羊草的消化结果相近(分别为71.29%、68.24%和11.74 MJ/kg)。花生秧的氮瘤胃有效降解率高于羊草和小麦秸,趋势与王雨菲等[28]和于胜晨等[29]的研究结果一致,但数值偏低(分别为57.24%、46.09%和27.77%),主要归因于试验原料的消化参数是根据体内试验测量值和INRA(2018)数据库的相关数值预测的,计算结果可能会受到饲粮交互作用以及INRA(2018)数据库中鱼粉和尿素等的瘤胃降解参数与本试验实际降解参数的差异影响。从3种粗饲料后肠消化率的套算值来看,羊草PDIA含量最高,说明羊草的RUP在肠道更易降解,这与袁翠林等[30]利用体外三步法预测这3种粗饲料RUP肠道消化率的趋势不一致(花生秧>羊草>小麦秸),这可以归因于体外试验与体内实际消化情况存在差异。羊草PDIA含量高于小麦秸和花生秧,而PDI含量低于小麦秸和花生秧,说明在肠道消化的羊草的MCP较少,可能是与羊草的瘤胃MCP合成量较低有关。结合蛋白质在肠道的消化情况来看,本试验套算值与INRA(2018)数据库仅有的粗饲料原料小麦秸的相应数值相比,OMd、DMD和代谢能等数值均较为接近,仅RPB值略低于INRA(2018)数据库利用原料组分的预测值,可能与本试验饲粮存在交互作用有关,也与INRA(2018)数据库中鱼粉、尿素等原料的降解率与实际存在差异有关。例如,INRA(2018)数据库饲料营养价值表中鱼粉的RD为50%,但根据相关研究发现,鱼粉的RD为30%~50%[31-32],又考虑实际套算过程中的局限性,鱼粉的RD取值为35%。

3.4 体内试验套算值与INRA(2018)模型预测值的比较分析

INRA(2018)体系对饲料原料营养参数的预测多提供2套模型,其一是根据鲜草的体内试验结果推测由同种饲料调制的青贮和干草的营养参数;其二是根据养分的化学分析结果预测。其中,OMd是估算VDMI、Ed和PDIM的共同基础,借助本试验所用饲粮纤维来源的唯一性,本文分别根据粗饲料自身养分含量(模型1)和半纯合饲粮NDF体内消化率(模型2)2种模型预测3种粗饲料的OMd,与根据体内试验套算法所得的OMd对比,并进一步比较3种算法所得的粗饲料VDMIm、Ed和DE间的差异,探讨体内试验结果的可靠性和INRA(2018)模型的适用性。
本试验中,根据模型2和半纯合饲粮套算法计算的3种粗饲料OMd数值趋势基本一致,但与模型1所得结果差异明显。利用模型1预测得到的羊草和花生秧OMd反而低于小麦秸,与前人的试验结果[33-34]不一致,也与实际生产常识相违;同时,以OMd为主要参数推算的3种粗饲料的VDMIm、Ed和DE也存在类似的矛盾,这可能与模型1建模时,为增加数据量仅根据草原牧草、禾本科和豆科3种粗饲料种类建立通用模型有关,不能充分反映具体饲料的特殊性,导致预测结果准确度降低。总而言之,INRA(2018)体系为不同种类粗饲料的营养价值预测提供了模型支持,通过引入干燥方式和收获茬次校正值,显著提升了预测的准确性和参考价值。此外,该体系还引入了小肠中不同来源蛋白质的消化量以及VDMI的概念,为优质饲料的选择和饲粮配方的优化提供了科学依据。然而,该体系在饲料分类方面仍存在不足,缺乏针对特殊饲料的预测模型,整体体系的完整性有待进一步完善。

4 结论

① 单一纤维来源半纯合饲粮试验结果表明,羊草和花生秧中的纤维成分比小麦秸更易于降解,因此其DMD、OMd和DE明显高于小麦秸。
② 根据INRA(2018)体系对3种粗饲料的营养价值进行评价,这3种粗饲料的RPB值均为负值,说明其瘤胃可降解蛋白质提供的氮均不足以满足该饲料OM通过瘤胃降解(或可发酵)合成MCP所需;小麦秸CP含量过低,导致其PDIA含量估算值为负值,也说明其在蛋白质营养价值上的劣势。
③ INRA(2018)体系的模型2对3种粗饲料OMd、Ed、DE和VDMIm的预测值与本试验的体内试验套算值接近,但模型1则相差甚远,不能反映饲料原本的特性,说明尽管INRA(2018)反刍动物饲喂体系构建了完整的饲料营养价值评价和营养需要量描述概念的模型体系,但部分模型的准确性及其使用范围尚需更多的探讨。

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