Chinese Journal of Animal Nutrition >

2025 , Vol. 37 >Issue 3: 2090 - 2100

DOI: https://doi.org/10.12418/CJAN2025.177

RESEARCH PAPER

Study on Nutritional Value, Rumen Degradation Rate, and in Vitro Gas Production of Jinmu Grain Grass Bag Storage

  • LIU Bing , 1 ,
  • ZHOU Keyang 1 ,
  • YANG Liyuan 1 ,
  • YAN Shilong 1 ,
  • MA Yuping 1 ,
  • WANG Yasong 2 ,
  • GONG Lei 2 ,
  • NIU Junli , 1, *
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  • 1 School of Animal Science and Technology, Shihezi University, Shihezi 832000, China
  • 2 Livestock and Veterinary Workstation of the First Division of Xinjiang Production and Construction Corps, Alar 832104, China
*associate professor, E-mail:

Received date: 2024-08-29

  Online published: 2025-03-13

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Abstract

The purpose of this experiment was to reveal the nutritional value of Jinmu grain grass bag storage by studying its fermentation quality, nutrient composition, rumen degradation characteristics and in vitro gas production, and to provide a theoretical basis for the processing and utilization of Jinmu grain grass. The fermentation period was 60 d with vacuum bags, and the bags were opened at 0, 3, 7, 15, 30 and 60 d, respectively, to determine the fermentation quality and nutrients. The rumen degradation characteristics and in vitro gas production of 60 d bags were studied by nylon bag method and batch culture in vitro. The results showed as follows: 1) the sensory evaluation of Jinmu grain grass after 60 days of ensiling was excellent. 2) With the extension of bag storage time, pH decreased gradually, ammonia nitrogen/total nitrogen (NH3-N/TN) and contents of lactic acid, acetic acid and propionic acid increased gradually (P<0.05). The pH of bagged for 60 days was significantly lower than that of 0, 3, 7 and 15 days (P<0.05), but there was no significant difference between 30 and 60 days (P>0.05). The contents of NH3-N/TN and lactic acid and acetic acid were significantly higher than those of 0 and 3 days after bag storage for 15 and 30 days (P<0.05), and the propionic acid content of bag storage for 60 days was significantly higher than that of 3, 7 and 15 days (P<0.05), but had no significant difference compared with 30 days (P>0.05). Butyric acid was not detected at time points. 3) The contents of dry matter (DM), crude fat (EE), crude protein (CP), neutral detergent fiber (NDF) and acid detergent fiber (ADF) were not significantly different among different bag storage time points (P>0.05). The relative feeding value (RFV) at 30 and 60 days was significantly higher than that at 0, 3, 7, 15 days (P>0.05). 4) The rumen DM degradation rate (74.97%), CP degradation rate (75.11%), NDF degradation rate (54.34%) and ADF degradation rate (48.81%) of Jinmu grain and grass bags stored for 72 h were significantly higher than those of Jinmu grain grass (P<0.05). The effective degradation rates of DM (50.11%), CP (51.09%), NDF (30.13%) and ADF (24.09%) were significantly higher than those of Jinmu grain grass bag storage (P<0.05). 5) The in vitro gas production of Jinmu grain grass bag storage at 72 h was significantly higher than Jinmu grain grass (P<0.05). In conclusion, the quality of Jinnmu grain grass forage stored in bags for 60 days is relatively high. Its main nutrients have a higher degradation rate in the rumen and produce a higher gas volume, making it an excellent forage resource for livestock and poultry.

Key words： Jinmu grain grass; bag storage; fermentation quality; nutritional components; rumen degradation rate; in vitro gas production

Cite this article

LIU Bing , ZHOU Keyang , YANG Liyuan , YAN Shilong , MA Yuping , WANG Yasong , GONG Lei , NIU Junli . Study on Nutritional Value, Rumen Degradation Rate, and in Vitro Gas Production of Jinmu Grain Grass Bag Storage[J]. Chinese Journal of Animal Nutrition, 2025 , 37(3) : 2090 -2100 . DOI: 10.12418/CJAN2025.177

我国反刍家畜养殖发展较快,优质饲草资源的开发与利用是制约草食类家畜发展的瓶颈,提高饲草加工利用是解决上述卡脖子问题的关键之一。金牧粮草生长速度快,再生性强,产量高[1],且其营养物质丰富,适口性好[2],是畜禽理想的饲料资源。青贮后的饲料柔软多汁、气味芳香,饲料营养价值提高[3],有利于提高畜禽采食量和消化利用率[4]。新疆种植的金牧粮草1年可收割3次,一般在8~11月完成,因此青贮加工可保证金牧粮草周年性供应和减少贮藏过程中营养损耗。通过尼龙袋法预测饲料在反刍动物瘤胃中的降解率,可反映饲料的可消化性[5]。体外产气法是评价饲料营养价值常用方法,通过体外产气特征的变化评估饲料的营养价值[6]。然而,金牧粮草青贮后营养价值与降解率等研究鲜有报道。因此,本研究通过探究金牧粮草袋贮发酵过程中青贮品质和营养成分的动态变化,结合金牧粮草袋贮体内外降解评价,旨在初步明确金牧粮草青贮营养价值,为其在畜禽生产上的推广和使用及我国畜牧业的健康可持续发展提供理论参考。

1 材料与方法

1.1 金牧粮草袋贮制作

在新疆生产建设兵团农一师八团收割金牧粮草(建植当年150 d,植株2.0 m左右)后,将新鲜采集金牧粮草人工切成1~2 cm小段,混合均匀后分别装入带有单向排气口的青贮发酵袋(30 cm×50 cm)中,密封后用抽气泵抽出发酵袋中气体,随后带回实验室,放置在遮荫避光处。

1.2 金牧粮草袋贮样品采集

分别在青贮0、3、7、15、30和60 d开袋取样。每次取5袋样品,每袋称取青贮饲料样品20 g置于250 mL锥形瓶中,加蒸馏水180 mL,于4 ℃冰箱中浸泡24 h,先用4层粗纱布过滤,再用滤纸精滤后获得浸提液[7]。其余青贮样分别称重后烘干,封存备用。

1.3 瘤胃降解率试验

选取石河子大学动物科技学院动物教学试验站3只健康的装有瘤胃瘘管的羊作为试验动物。本试验已获得石河子大学动物福利委员会的批准(伦理编号: A2023-226)。羊每天饲喂3次(07:00、13:00和19:00),自由饮水。准确称取3.00 g金牧粮草及其袋贮60 d的金牧粮草放入尼龙袋(孔径40~50 μum,尺寸6 cm×9 cm)中,每2个袋子夹在1根长约12 cm的半软塑料管上,用橡皮筋牢牢地固定在一起。在其进食后2 h,将尼龙袋投放到瘤胃腹囊处,管的另一端用尼龙绳系在瘘管架上[8]。每只羊都进行3次重复试验,其中每次试验在晨饲前(08:00)进行样品投放,分别在投放2、4、8、12、24、48和72 h时,迅速取出尼龙袋并进行彻底清洗干净,然后将其在65 ℃下烘干至恒重状态[9]。另取3只尼龙袋,放入3.00 g样品,但未放入瘤胃中,经过反复冲洗后,同样在65 ℃下烘干至恒重,作为0 h的对照样品[10]。

1.4 体外产气试验

在上述试验羊晨饲后的2 h内,通过瘤胃瘘管采集3头羊的瘤胃液,将其混合后装入瓶中保温回实验室。在实验室中,使用4层纱布过滤瘤胃液同时通入CO2气体,确保操作环境厌氧。所有操作均在39 ℃水浴中迅速完成,以尽量减少操作时间。
使用精密天平准确称量200 mg金牧粮草及其袋贮60 d样品。将称量好的样品送入体外发酵注射器中,每个样品取6个平行样本,每批培养中有6个空白样品(只有培养液,没有饲料样品)。称取完所有样品后,在注射器活塞的前1/3部分涂抹适量医用凡士林以防止漏气,但要尽量减少气体产生过程中活塞上升的阻力[11]。将样品轻轻地装入注射器中,确保不要使其溅出来,同时夹住胶管,避免样品从注射器口溢出。在39 ℃的电热恒温水浴箱中预热30 min。
将瘤胃液与人工培养液按照1∶2的体积比例混合,形成混合人工瘤胃液。混合液在搅拌的同时通入CO2。使用自动加液器向每个注射器中注入30 mL混合人工瘤胃液。用铁架台竖直向上固定玻璃培养管的进液端,排除容器内气体,并用铁夹夹住胶管前端,并记录下初始刻度值。迅速将培养管放入预热至39 ℃的水浴箱中。待加液完成后,将所有注射器成批转移到39 ℃恒温培养箱中[12]。

1.5 指标检测

1.5.1 感官评定

按照《青贮饲料质量评分标准(试行)》[13]对袋贮60 d的样品进行感官评定。从色泽、气味和质地对袋贮饲料进行感官评价。

1.5.2 袋贮发酵品质的测定

用袋贮浸提液测定pH和氨态氮(NH3-N)含量。pH利用酸度计测定;NH3-N含量采用苯酚-次氯酸钠比色法[14]测定。乳酸(lactic acid, LA)、乙酸(acetate acid, AA)、丙酸(propionic acid, PA)和丁酸(butyric acid, BA)含量采用高效液相色谱法[7](Agi-Lent1260高效液相色谱仪,美国安捷伦科技公司)测定。

1.5.3 营养成分测定

袋贮营养品质指标主要测定干物质(dry matter, DM)、粗脂肪(ether extract, EE)、粗蛋白质(crude protein, CP)、中性洗涤纤维(neutral detergent fiber, NDF)和酸性洗涤纤维(acid detergent fiber, ADF)含量。其中DM、CP和EE含量分别按照国标GB/T 6435—2014、GB/T 6432—2018和GB/T 6433—2006方法进行测定,NDF和ADF含量参照Van Soest等[15]方法进行测定。按照下列公式计算相对饲喂价值(relative feed value, RFV)。
RFV=DMI×DDM/1.29;
DMI=120/NDF;
DDM=88.9-0.779×ADF。
式中:DMI为DM随意采食量(%BW);DDM为可消化DM含量(%DM),1.29是饲草DMI×DDM的参数值。

1.5.4 瘤胃降解率

袋贮60 d饲料样本的瘤胃降解率按照王加启[16]的尼龙袋方法操作。主要测定干物质降解率(dry matter degradation rate, DMD)、粗蛋白质降解率(crude protein degradation rate, CPD)中性洗涤纤维降解率(neutral detergent fiber degradation rate, NDFD)、酸性洗涤纤维降解率(acid detergent fiber degradation rate, ADFD)。按以下饲料成分瘤胃降解率公式计算袋贮饲料样品中DM、CP、NDF和ADF的不同时间点的瘤胃降解率(%)。
不同时间点的某饲料营养成分的瘤胃降解率(%)=[(未降解前尼龙袋内的营养物质的量-降解后尼龙袋内剩余物中营养物质的量)/未降解前尼龙袋内的营养物质的量]×100。
饲料成分的瘤胃降解参数按照Ørskov等[17]提出的数学指数模型计算:
dp=a+b(1-e-ct)。
式中:dp为饲料样品在瘤胃降解t时间后某营养成分的降解率(%);a为快速降解部分(%);b为慢速降解部分(%);c为慢速降解部分的降解率(%/h);t为饲料在瘤胃内停留时间。
根据此公式,代入不同时间点的饲料样品的瘤胃降解率,利用最小二乘法的原理,计算出瘤胃降解参数a、b和c,计算饲料成分的有效降解率:
P=a+bc/(c+k)。
式中:P为有效降解率(%);a为快速降解部分(%);b为慢速降解部分(%);c为慢速降解部分的降解率(%/h);k为饲料的外流速度;金牧粮草的k值取0.025 39[18]。

1.5.5 体外产气量

参照Menke等[19]体外产气法模拟瘤胃发酵培养。分别于培养后2、4、6、8、10、12、18、24、30、36、42、48、60、72 h通过玻璃注射器记录产气量。从产气开始后,每隔一段时间通过玻璃注射器记录一次产气量,每次记录后放气并将玻璃注射器的刻度归零[20]。将72 h内的产气量累加起来,得到72 h内的累计产气量。

1.6 数据分析

使用Excel 2016软件对所有样本的测定值进行整理,使用SPSS 22.0软件进行单因素方差分析(one-way ANOVA),袋贮时间对试验结果的影响进行了一次线性和二次曲线趋势检验,使用t检验进行差异显著性检验,结果以平均值和标准误(SE)表示,P<0.05表示差异显著。

2 结果与分析

2.1 金牧粮草袋贮感官评定

袋贮60 d后对袋贮感官进行打分并进行评级。由表1可知,金牧粮草袋贮60 d的气味、色泽和质地均达到优等的效果。
表1 袋贮60 d的金牧粮草品质鉴定

Table 1 Quality identification of Jinmu grain grass with bag storage 60 d

时间Time 色泽Color 气味Smell 质地Texture 等级Grade
60 d 黄绿色 酸香味 松散不黏手 优等

2.2 不同袋贮时间对金牧粮草发酵品质的影响

由表2可知,袋贮60 d的pH显著低于0、3、7和15 d(P<0.05),30 d的pH显著低于0、3和7 d(P<0.05),袋贮15 d的pH显著低于0和3 d(P<0.05),7 d的pH显著低于0 d(P<0.05);袋贮7、15、30和60 d的NH3-N/TN均显著高于0和3 d(P<0.05);袋贮15和30 d乳酸含量均显著高于0和3 d(P<0.05);袋贮7、15、30和60 d乙酸含量均显著高于0 d(P<0.05);袋贮0 d丙酸含量未检出,60 d含量显著高于3、7、15 d(P<0.05),与30 d差异不显著(P>0.05);各时间点均未检出丁酸。
表2 不同袋贮时间金牧粮草的发酵品质

Table 2 Fermentation quality of Jinmu grain grass with different bag storage time

项目
Items		 0 d 3 d 7 d 15 d 30 d 60 d 标准误
SE		 P值P-value
处理
Treatment		 线性
Linear		 二次
Quadratic
pH 6.16a 5.47b 5.06bc 4.51cd 4.33de 4.01e 0.093 <0.001 0.032 0.524
氨态氮/总氮
NH3-N/TN/%		 0.93e 3.07d 3.42c 3.89bc 4.32b 5.08a 1.033 <0.001 0.017 0.681
乳酸LA/% DM 0.54a 1.07de 1.77d 2.94c 5.37b 6.57a 0.915 <0.001 0.024 0.985
乙酸AA/% DM 0.29d 0.84cd 1.07c 1.12c 2.08b 2.77a 0.487 0.017 0.018 0.622
丙酸PA/% DM ND 0.04b 0.05b 0.06b 0.07ab 0.08a 0.006 0.001 0.065 0.377
丁酸BA/% DM ND ND ND ND ND ND

同行数据肩标不同小写字母表示差异显著(P<0.05)。表3同。ND:未检出。

In the same row, values with different lowercase letter superscripts mean significant difference (P<0.05). The same as Table 3. ND: not detected.

2.3 不同袋贮时间对金牧粮草营养成分和RFV的影响

由表3可知,不同袋贮时间点之间DM、CP、EE、NDF和ADF含量均差异不显著(P>0.05);袋贮30和60 d的RFV显著高于0、3、7、15 d(P>0.05),0、3、7、15 d之间差异不显著(P>0.05)。
表3 不同袋贮时间金牧粮草的营养成分和相对饲喂价值

Table 3 Nutrients and RFV of Jinmu grain grass with different bag storage time

项目
Items		 0 d 3 d 7 d 15 d 30 d 60 d 标准误
SE		 P值P-value
处理
Treatment		 线性
Linear		 二次
Quadratic
干物质DM/% 18.47 18.64 19.50 19.35 17.82 17.07 1.351 0.244 0.351 0.021
粗蛋白质CP/% DM 11.62 10.32 10.11 7.93 9.49 9.31 0.954 0.679 0.542 0.378
粗脂肪EE/% DM 10.45 11.05 10.74 10.69 10.54 10.54 1.326 0.750 0.658 0.874
中性洗涤纤维NDF/% DM 75.04 75.17 75.06 74.64 74.04 73.55 5.761 0.297 0.414 0.065
酸性洗涤纤维ADF/% DM 42.78 42.70 42.36 41.88 41.01 40.77 1.791 0.294 0.058 0.642
相对饲喂价值RFV 68.89b 68.85b 69.28b 70.14b 71.56a 72.27a 2.170 0.048 0.322 0.071

2.4 金牧粮草及其袋贮营养物质瘤胃降解率

由表4可知,与金牧粮草相比,金牧粮草袋贮的DM瘤胃降解率明显高于前者,在72 h时金牧粮草袋贮DM瘤胃降解率为74.97%,显著高于金牧粮草(P<0.05);在6~48 h,2种饲料的DM瘤胃降解率升高速度加快,说明金牧粮草及其袋贮DM在瘤胃中降解率较高。金牧粮草袋贮的CP瘤胃降解率显著高于金牧粮草(除了12 h)(P<0.05),在2~48 h,2种饲料的CP瘤胃降解率升高幅度增大,随后瘤胃降解率比较稳定,72 h时金牧粮草袋贮和金牧粮草CP瘤胃降解率分别为75.11%和68.10%。金牧粮草袋贮NDF和ADF瘤胃降解率在不同时间点(除了6 h)上均显著高于金牧粮草(P<0.05),NDF和ADF瘤胃降解率在2~6 h时增幅较慢,在72 h时金牧粮草袋贮和金牧粮草NDF瘤胃降解率分别为54.34%和50.32%,ADF瘤胃降解率分别为48.81%和45.02%。
表4 金牧粮草及其袋贮瘤胃降解率

Table 4 Rumen degradation rate of Jinmu grain grass and its bag forage %

项目Items 2 h 6 h 12 h 24 h 36 h 48 h 72 h
干物质瘤胃降解率DM rumen degradation rate
金牧粮草Jinmu grain grass 17.95b 20.59b 25.75b 36.17b 48.48b 60.23b 67.86b
金牧粮草袋贮Jinmu grain grass bag forage 20.13a 23.12a 31.49a 45.00a 55.78a 66.40a 74.97a
标准误SE 1.232 2.091 2.011 1.872 2.977 3.001 2.861
P值P-value 0.021 0.029 0.041 0.040 0.009 0.008 0.025
粗蛋白质瘤胃降解率CP rumen degradation rate
金牧粮草Jinmu grain grass 19.58b 25.88b 32.08 43.59b 55.29b 64.80b 68.10b
金牧粮草袋贮Jinmu grain grass bag forage 22.18a 28.33a 37.17 52.48a 60.44a 69.90a 75.11a
标准误SE 0.921 2.980 2.173 3.001 2.561 1.762 2.343
P值P-value 0.032 0.017 0.087 0.040 0.042 0.009 0.036
中性洗涤纤维瘤胃降解率NDF rumen degradation rate
金牧粮草Jinmu grain grass 15.47b 19.00b 26.55b 35.34b 40.61b 55.48a 50.32b
金牧粮草袋贮Jinmu grain grass bag forage 18.46a 21.21a 28.17a 39.22a 45.37a 50.25b 54.34a
标准误SE 1.222 1.543 2.091 2.421 1.675 3.091 1.654
P值P-value 0.040 0.001 <0.001 0.005 0.024 0.039 0.015
酸性洗涤纤维瘤胃降解率ADF rumen degradation rate
金牧粮草Jinmu grain grass 14.33b 16.50 21.96b 30.62b 34.81b 40.64b 45.02b
金牧粮草袋贮Jinmu grain grass bag forage 17.29a 19.47 24.32a 33.81a 37.67a 42.12a 48.81a
标准误SE 0.002 0.872 1.002 2.321 2.071 1.982 1.245
P值P-value 0.029 0.832 0.037 0.009 0.016 0.024 0.044

同一个项目同列数据肩标不同小写字母表示差异显著(P<0.05)。表5同。

In the same column and item, values with different lowercase letter superscripts mean significant difference (P<0.05). The same as Table 5.

2.5 金牧粮草及其袋贮营养物质瘤胃降解参数

由表5可知,金牧粮草袋贮的DM、CP、NDF和ADF降解参数大部分存在显著差异(P<0.05),除了DM慢速降解部分和ADF快速降解部分,金牧粮草袋贮DM、CP、NDF和ADF快速降解部分、慢速降解部分、潜在可降解部分以及有效降解率均显著高于金牧粮草(P<0.05)。金牧粮草及其袋贮DM、CP、NDF和ADF有效降解率分别为43.41%和50.11%、44.09%和51.09%、26.01%和30.13%以及21.07%和24.09%。
表5 金牧粮草及其袋贮瘤胃降解参数

Table 5 Rumen degradation parameters of Jinmu grain grass and its bag forage

项目Items a/% b/% c/(%/h) a+b/% P/%
干物质瘤胃降解参数DM rumen degradation parameters
金牧粮草Jinmu grain grass 12.01b 50.83 0.040 9b 60.84b 43.41b
金牧粮草袋贮Jinmu grain grass bag forage 15.60a 53.32 0.046 4a 68.92a 50.11a
标准误SE 0.998 1.012 0.001 3.983 2.861
P值P-value 0.001 0.191 <0.001 0.026 0.033
粗蛋白质瘤胃降解参数CP rumen degradation parameters
金牧粮草Jinmu grain grass 15.65b 44.30b 0.045 4b 59.95b 44.09b
金牧粮草袋贮Jinmu grain grass bag forage 17.88a 49.93a 0.050 3a 67.81a 51.09a
标准误SE 2.561 2.901 0.001 3.451 2.015
P值P-value 0.047 0.032 0.007 0.005 0.025
中性洗涤纤维瘤胃降解参数NDF rumen degradation parameters
金牧粮草Jinmu grain grass 11.56b 30.56b 0.022 5b 42.25b 26.01b
金牧粮草袋贮Jinmu grain grass bag forage 14.42a 31.52a 0.025 1a 45.94a 30.13a
标准误SE 0.122 2.761 0.000 3.976 2.451
P值P-value 0.002 0.001 <0.001 0.035 0.019
酸性洗涤纤维瘤胃降解参数ADF rumen degradation parameters
金牧粮草Jinmu grain grass 9.49 25.62b 0.020 9b 35.11b 21.07b
金牧粮草袋贮Jinmu grain grass bag forage 11.41 26.84a 0.022 7a 38.25a 24.09a
标准误SE 0.012 2.311 0.000 2.051 1.782
P值P-value 0.871 0.031 0.018 0.004 0.007

a:快速降解部分;b:慢速降解部分;c:慢速降解部分的降解率;a+b:潜在可降解部分;P:有效降解率。

a: fast degradation part; b: slow degradation part; c: the degradation rate of the slow degradation part; a+b: potential degradation part; P: effective degradation rate.

2.6 金牧粮草及其袋贮体外积累产气量

由图1可知,金牧粮草和金牧粮草袋贮随着体外发酵时间的延长产气量逐渐上升,在72 h时体外产气量均达到最高,且产气量趋于稳定,金牧粮草袋贮体外产气量为90 mL,显著高于金牧粮草(P<0.05)。
图1 金牧粮草及其袋贮体外产气曲线

相同时间点标注不同字母表示差异显著(P<0.05)。

Fig.1 Gas production curve of Jinmu grain grass and its bag storage in vitro

Different letters at the same time point indicated that the difference was significant (P<0.05).

3 讨论

3.1 不同袋贮时间对金牧粮草的发酵品质以及营养价值的影响

青贮是指将青绿饲料原料通过微生物发酵的方法,使饲料能够长期保存,同时营养得到最大程度保留的一项技术[21-22]。本试验对金牧粮草袋贮60 d后的色泽、气味和质地进行评价,结果颜色为黄绿色,有酸香味,松散不黏手,综合评级达到优级。
青贮过程中产生大量的有机酸,使pH迅速降低,抑制有害菌生长,将饲料的营养成分保存下来[23-24]。全株谷草青贮60 d时,pH及乳酸和可溶性碳水化合物含量达到稳定状态,因此建议全株谷草青贮最短启用时间为60 d[25-26]。一般认为,优质青贮饲料的pH应低于4.2,本试验袋贮60 d时金牧粮草的pH为4.13,表明其青贮效果良好。
青贮饲料中蛋白质及氨基酸分解的程度通常用NH3-N/TN反映,比值越大,表明CP降解越多[27]。一般情况下,若NH3-N/TN在1/10以下,则表明发酵过程良好。随着青贮时间的延长,虽然NH3-N/TN越来越高,但比值一直在10%以下[28]。本试验中随着袋贮时间延长,NH3-N/TN逐渐增大,但变化范围在可以接受的范围内[29-30],表明袋贮过程储存较好,抑制了微生物的活动,降低了对蛋白质的降解过程。但试验中NH3-N/TN增加的速度持续加快,如此可能会影响饲料的营养价值和适口性,同时也会增加动物消化系统的负担,还需进一步试验验证。
较好的青贮饲料应该含有较多的乳酸,少量乙酸,而不含丁酸。乙酸是由醋酸菌产生和乳酸进一步分解而来的,在初期可以抑制有害微生物的繁殖,但过量则影响饲料的适口性[31]。青贮中产生不同酸表明发酵过程中有多种微生物进行发酵,可以显著降低青贮饲料的pH,延长青贮饲料有氧质变的时间[32]。从本试验袋贮有机酸含量结果可以看出,金牧粮草袋贮的乳酸含量均高于乙酸含量,且均未检测出丁酸,说明金牧粮草袋贮为乳酸发酵类型,且产生的大量乳酸不仅有效抑制了其他微生物,还改良了饲料适口性,延长了饲料的保质时间[31]。
通常认为,青饲料适时青贮,其营养成分一般仅损失10%左右[33]。本试验结果表明,不同袋贮时间金牧粮草的常规营养成分差异不显著,而袋贮30和60 d的RFV显著高于其他时间,说明金牧粮草袋贮过程营养物质损失较少。
此外,从本试验结果可以看出金牧粮草发酵品质和营养成分含量均随着袋贮时间的延长表现出持续增加或降低的趋势,表明金牧粮草在袋贮60 d时并未达到稳定状态,这提示金牧粮草袋贮时间需要延长,或许传统青贮方法并不适用于金牧粮草,但这仍待进一步研究。

3.2 金牧粮草袋贮营养物质瘤胃降解率

营养物质降解率可反映各营养物质被动物消化吸收程度,降解率越高,饲料的可利用程度越高[34],其与产气量、体内消化率存在高度相关性[35-36]。研究金牧粮草营养成分在瘤胃中降解率和降解参数对于揭示其营养价值至关重要。饲草DM在瘤胃中降解率的大小是饲草瘤胃降解率的科学指标,DM降解率的高低反映着饲料在瘤胃中消化的难易程度[37]。饲草CP在瘤胃中的降解率与在瘤胃滞留时间、饲草CP含量以及其细胞壁纤维结构成熟度有关。本试验中,金牧粮草及其袋贮6~48 h的DM和CP的瘤胃降解率变化幅度较大,且金牧粮草袋贮DM和CP瘤胃有效降解率高于金牧粮草。在反刍动物饲养管理中,饲料纤维含量,尤其是NDF和ADF,对瘤胃消化功能和营养状态有显著影响。高NDF含量可能导致采食量下降和填充效应增强,而高ADF含量则降低消化率。通过控制NDF和ADF含量,可以调控采食行为和消化功能。NDF和ADF含量通常与瘤胃微生物的增长和代谢活动呈正相关。这些纤维成分为微生物提供了必要的碳源和能源,有助于维持瘤胃内的微生态平衡。NDF与ADF的降解率高低反映了粗饲料的消化难易程度。本试验中金牧粮草袋贮72 h的NDF和ADF瘤胃降解率高于金牧粮草,且有效降解率亦显著高于金牧粮草,猜测可能是金牧粮草袋贮的纤维物质更容易被瘤胃微生物利用[38],而具体原因仍需进一步研究确定。

3.3 金牧粮草及其袋贮体外累积产气量

体外发酵产生的气体主要是二氧化碳和甲烷,主要是由饲草中的碳水化合物和CP产生[39]。产气量能够反映饲草的可发酵程度,主要受可发酵有机物含量和瘤胃微生物活性的影响[40]。饲草的品质越好,瘤胃产气量也越高[41]。本试验中72 h时金牧粮草袋贮的体外产气量显著高于金牧粮草,表明袋贮后金牧粮草的可消化性提高[42],这可能与纤维物质降解率提高有关[43]。

4 结论

随着袋贮时间的延长,金牧粮草袋贮的pH、NH3-N/TN、乳酸、乙酸和丙酸含量提高,且袋贮60 d金牧粮草感官评定为优等,金牧粮草袋贮营养物质瘤胃降解率及体外产气量均显著高于金牧粮草,表明袋贮可提高金牧粮草营养价值。

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