Effects of Planting Density and Additives on Fermentation Quality, Nutrients and in Vitro Digestibility of Four Varieties of Whole Corn Silage in Tongliao Area

CHEN Xue; ZHANG Hongrui; WANG Yifan; JI Fangcai; WANG Lei; BAO Jinze; ZHUO Xingliang; JIA Tingting; YU Zhu

doi:10.12418/CJAN2024.172

2024 , Vol. 36 >Issue 3: 1977 - 1986

DOI: https://doi.org/10.12418/CJAN2024.172

RESEARCH PAPER

Effects of Planting Density and Additives on Fermentation Quality, Nutrients and in Vitro Digestibility of Four Varieties of Whole Corn Silage in Tongliao Area

CHEN Xue ,
ZHANG Hongrui ,
WANG Yifan ,
JI Fangcai ,
WANG Lei ,
BAO Jinze ,
ZHUO Xingliang ,
JIA Tingting ,
YU Zhu ^,^*

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College of Grassland and Technology, China Agricultural University, Beijing 100193, China

*professor, E-mail: yuzhu33150@sina.com

Received date: 2023-10-11

Online published: 2024-03-13

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Abstract

This experiment was conducted to study the effects of varieties, planting density and additives on fermentation quality, nutrients and in vitro digestibility of whole corn silage in Tongliao area. The whole corn silage was prepared using whole corn cultivars of “Dakang 205”, “Gaoyou 958”, “Zhongyu 335” and “Zhongnong 787” as materials, two planting density of 6.75×10⁴ and 8.25×10⁴ plants/hm² was set, and Lentilactobacillus buchneri was added after corn harvest. After 200 days of fermentation at room temperature, the fermentation quality, conventional nutrients and in vitro digestibility were determined, and the correlation analysis method was used to evaluate the silage quality. The results showed as follows: 1) the pH of 4 varieties of whole corn silage was below 4.0; the acetic acid (AA) content of “Gaoyou 958” silage was significantly higher than that of “Dakang 205” silage (P<0.05), and the ammonia nitrogen (NH₃-N) content was significantly lower than that of the other varieties (P<0.05). The fermentation quality of whole corn silage with 8.25×10⁴ plants/hm² planting density was better than that of whole corn silage with 6.75×10⁴ plants/hm² planting density. The contents of lactic acid (LA) and AA in whole corn silage supplemented with Lentilactobacillus buchneri were higher than those without additive (P>0.05). 2) The contents of dry matter (except “Gaoyou 958”) and starch of “Dakang 205” silage were higher than those of the other varieties (P<0.05), the contents of neutral detergent fiber (NDF) and acid detergent fiber were the lowest, and significantly lower than those of “Zhongyu 335” silage (P<0.05); the nutritional quality of “Gaoyou 958” silage was inferior to that of “Dakang 205” silage. The nutritional quality of whole corn silage with 8.25×10⁴ plants/hm² planting density was better than that of whole corn silage with 6.75×10⁴ plants/hm² planting density. The nutritional quality of silage was improved after Lentilactobacillus buchneri was added. 3) The in vitro dry matter digestibility (IVDMD) of “Gaoyou 958” silage was the highest, which was significantly higher than that of “Dakang 205” and “Zhongyu 335” silages (P<0.05). 4) The contents of NDF and ADF of whole corn silage were significantly positively correlated with contents of LA and AA (P<0.05), the NH₃-N content was significantly negatively correlated with pH and IVDMD (P<0.05). In conclusion, the silage quality of “Dakang 205” and “Gaoyou 958” varieties is better, and the whole corn silage with high planting density of 8.25×10⁴ plants/hm² has higher nutrient contents, and the fermentation quality of whole corn silage can be improved by adding Lentilactobacillus buchneri. The comprehensive evaluation shows that “Gaoyou 958” is suitable to be used as silage corn in Tongliao area.

Key words： corn varieties; planting density; additive; silage quality

Cite this article

CHEN Xue , ZHANG Hongrui , WANG Yifan , JI Fangcai , WANG Lei , BAO Jinze , ZHUO Xingliang , JIA Tingting , YU Zhu . Effects of Planting Density and Additives on Fermentation Quality, Nutrients and in Vitro Digestibility of Four Varieties of Whole Corn Silage in Tongliao Area[J]. Chinese Journal of Animal Nutrition, 2024 , 36(3) : 1977 -1986 . DOI: 10.12418/CJAN2024.172

青贮玉米一直是反刍动物饲料中重要的粗饲料来源^[1],已成为全球使用最广泛的青贮原料^[2]。全株玉米生物产量高,具有可溶性碳水化合物(water soluble carbohydrate,WSC)含量高、营养丰富、适口性好、易加工以及耐贮藏等优点^[3],其青贮质量受品种、收获期和添加剂等因素的影响^[4]。青贮玉米品种本身的遗传特性是影响青贮品质的主要因素^[5],不同品种的全株玉米适宜的栽培密度也不同,其青贮效果的差异也较大。由于光热条件不同,同一青贮玉米品种在不同地区的生长表现也不同^[6]。通辽地区用于青贮调制的全株玉米品种多,但品质差别较大。由于品种的多样性,养殖业和小型农户选择青贮用玉米品种一般是依据经验或他人推荐,所以农民选择品种具有盲目性,进而严重影响种植青贮玉米的收益。因此,选择适应当地的优质青贮玉米品种和合理的种植密度,能够帮助养殖企业和农牧民选择青贮玉米品种。

此外,玉米青贮时使用添加剂可以提高青贮饲料的营养价值,降低干物质(dry matter,DM)损失,提高青贮饲料消化率^[7]。近年来,随着青贮饲料添加剂的研究和应用越来越多,青贮饲料的发酵品质和营养价值逐步提升^[8]。玉米在自然生长的状态下附着的乳酸菌数量较少,但酵母菌和霉菌等不利于青贮发酵的有害微生物较多,利用布氏乳杆菌(Lentilactobacillus buchneri,LB)制作的微生物添加剂可以在青贮发酵过程发挥作用,将产生的乳酸(lactic acid,LA)降解为具有抗真菌特性的乙酸(acetic acid,AA),使pH下降^[9],抑制有害微生物增殖,从而提高青贮饲料发酵品质^[10]。因此,选择适宜青贮玉米的品种、种植密度和青贮添加剂可以在生产和加工层面促进农民增收和企业增效。

本研究以通辽地区4个玉米品种为研究对象,在不同种植密度下进行播种,收获后添加微生物菌剂青贮,测定青贮前后发酵品质、营养成分和体外消化率,并运用相关性分析和主成分分析方法对全株玉米青贮进行综合评价,旨在筛选出通辽地区适栽的青贮玉米品种、种植密度和添加剂,以期为该地区全株玉米种植提供理论依据。

1 材料与方法

1.1 试验材料

本试验地位于内蒙古通辽市科尔沁左翼中旗国家现代农业产业园区,海拔178 m。供试青贮玉米品种有4个,分别是:“大康205”、“高油958”、“中玉335”和“中农787”。种植期间设置2个种植密度,分别是低密度和高密度(低密度为6.75×10⁴株/hm²,采用大垄宽0.8 m,小垄宽0.4 m,株距25 cm;高密度为8.25×10⁴株/hm²,采用大垄宽0.8 m,小垄宽0.4 m,株距20 cm。滴灌带浅埋于小垄中间2~4 cm。田间南北设有过道,相邻品种间空1垄)。种植玉米于乳熟中期至蜡熟期收获,进行青贮调制。

1.2 青贮调制方法

青贮玉米于2021年5月31日播种,种植112 d,在2021年9月20日刈割,收获时“中玉335”和“中农787”处于乳熟期、“大康205”和“高油958”处于蜡熟期,当地气温1~13 ℃。将收获后的玉米原材料粉碎切短至2~3 cm,然后进行添加剂处理:1)添加布氏乳杆菌,添加量为1×10⁶ CFU/g FM,由中国农业大学牧草生产与加工利用实验室提供;2)无添加剂(CK)作为对照,添加等量蒸馏水。每个青贮桶装入原料2 400 g(每个青贮桶容积为3 L),将原料与添加剂混合均匀后装入青贮桶中,青贮密度=2 400 g/3 L=800 kg/m³,每个处理3个重复,室温下发酵200 d。

1.3 测定指标及方法

1.3.1 发酵品质

开罐后取样品20 g进行分析,倒入180 mL蒸馏水均匀搅拌,于4 ℃下浸提24 h后过滤得浸提液,立即用pH计(pHS-3C)测定浸提液pH,置于-20 ℃条件下保存备用。采用高效液相色谱法(HPLC)测定LA、AA、丙酸(propionic acid,PA)和丁酸(butyric acid,BA)含量,采用苯酚-次氯酸钠比色法测定氨态氮(ammonia nitrogen,NH₃-N)含量,利用粗蛋白质(crude protein,CP)测定的全氮来计算氨态氮/总氮(total nitrogen,TN)^[11]。

1.3.2 营养成分

将全株玉米青贮料烘干粉碎,过40目筛,用于测定营养成分含量,结果以DM计。采用杨胜^[12]的方法测定DM含量;采用AOAC(2003)测定WSC含量^[13];采用范氏洗涤纤维法^[14]测定中性洗涤纤维(neutral detergent fiber,NDF)和酸性洗涤纤维(acid detergent fiber,ADF)含量;采用高氯酸水解-蒽酮比色法^[15]测定淀粉(starch,ST)含量。

1.3.3 体外消化率

试验瘤胃液供体取自北京中地畜牧科技有限公司的3头荷斯坦奶牛。晨饲前取瘤胃液于保温瓶中,迅速带回实验室,经过4层纱布过滤放入39 ℃预热过的收集瓶,通入二氧化碳(CO₂)。参照McDougll’s法^[16]配制pH为6.80的缓冲液,按照缓冲液∶瘤胃液体积比为4∶1混合成培养液,取50 mL培养液注入含0.5 g样品的培养瓶内,通入CO₂,立即盖上胶塞和铝盖,使用专用封口钳压紧,39 ℃恒温振荡(100 r/min)培养48 h后,测定体外干物质消化率(in vitro dry matter digestibility,IVDMD)和体外中性洗涤纤维消化率(in vitro neutral detergent fiber digestibility,IVNDFD)。

1.4 数据统计分析

试验数据经Excel 2019整理后,采用SPSS 22.0软件的双因素方差分析(two-way ANOVA)过程分析品种、种植密度和添加剂处理及其交互作用对全株玉米青贮饲用品质的影响,P<0.05表示差异显著。全株玉米青贮发酵品质和营养成分含量的相关性选择Pearson相关性分析,采用Hit Plot软件进行相关性绘图。

2 结果与分析

2.1 品种、种植密度和添加剂对全株玉米青贮发酵品质的影响

由表1可知,品种对全株玉米青贮发酵品质各指标均有显著影响(P<0.05)。“大康205”青贮的pH显著低于“高油958”和“中农787”青贮(P<0.05),所有品种的全株玉米青贮后pH都在4.0以下;“中玉335”青贮的LA和AA含量最高,其中LA含量显著高于“大康205”和“高油958”青贮,AA含量显著高于“大康205”青贮(P<0.05);“高油958”青贮的NH₃-N含量显著低于其他品种(P<0.05),PA含量显著高于“大康205”和“中玉335”青贮(P<0.05);“中玉335”青贮的BA含量最高,显著高于其他品种(P<0.05)。总体来看,“大康205”和“高油958”在6.75×10⁴株/hm²种植密度以及添加布氏乳杆菌时全株玉米青贮发酵品质优于其他处理。从种植密度平均值来看,8.25×10⁴株/hm²种植密度全株玉米青贮发酵品质优于6.75×10⁴株/hm²种植密度。从添加剂平均值来看,添加布氏乳杆菌的全株玉米青贮LA和AA含量高于无添加剂(P>0.05)。此外,品种和种植密度对全株玉米青贮的pH以及NH₃-N、AA、LA和PA含量有显著交互作用(P<0.05),品种、种植密度和添加剂对PA和BA含量有显著交互作用(P<0.05)。

表1 品种、种植密度和添加剂对全株玉米青贮发酵品质的影响

Table 1 Effects of varieties, planting density and additives on fermentation quality of whole corn silage

品种 Varieties	种植密度 Planting density	添加剂 Additives	pH	氨态氮 NH₃-N/ (% TN)	乳酸 LA/ (% DM)	乙酸 AA/ (% DM)	丙酸 PA/ (% DM)	丁酸 BA/ (% DM)
大康205 Dakang 205	高 High	CK	3.78^de	5.39^a	2.58^c	0.65^d	0.17^ef	0.07^cde
		LB	3.80^bcde	5.02^ab	2.75^c	0.96^cd	0.25^def	0.05^de
	低 Low	CK	3.77^de	4.97^ab	4.15^abc	1.27^bcd	0.41^bcd	0.08^bcde
		LB	3.79^cde	5.38^a	3.22^bc	1.34^bcd	0.11^ef	0.05^de
中玉335 Zhongyu 335	高 High	CK	3.74^e	5.07^ab	6.06^a	2.49^ab	0.16^ef	0.13^ab
		LB	3.80^bcde	4.76^ab	5.68^ab	2.71^a	0.09^f	0.10^bcd
	低 Low	CK	3.92^abc	3.32^cd	2.81^c	1.31^bcd	0.12^ef	0.08^bcde
		LB	3.94^ab	4.14^bc	3.72^abc	1.77^abcd	0.24^def	0.16^a
高油958 Gaoyou 858	高 High	CK	3.93^abc	3.45^cd	3.61^abc	1.79^abcd	0.43^bcd	0.07^cde
		LB	3.89^abcd	3.40^cd	3.12^c	1.37^bcd	0.06^f	0.04^e
	低 Low	CK	3.92^abc	3.18^cd	2.89^c	1.29^bcd	0.35^cde	0.12^abc
		LB	3.98^a	2.79^d	3.21^bc	2.58^a	1.06^a	0.10^bcd
中农787 Zhongnong 787	高 High	CK	3.88^abcde	3.89^bcd	3.28^bc	1.94^abc	0.10^f	0.05^cde
		LB	3.88^abcde	3.49^cd	3.96^abc	1.50^abcd	0.44^bcd	0.06^cde
	低 Low	CK	3.86^abcde	4.24^abc	4.32^abc	1.61^abcd	0.65^b	0.09^bcde
		LB	3.81^bcde	4.11^bc	4.31^abc	1.93^abc	0.49^bc	0.07^cde
标准差 SD			0.01	0.32	0.06	0.04	0.01	0.00
品种平均值 Mean of varieties
大康205 Dakang 205			3.79^c	5.19^a	3.17^b	1.05^b	0.23^bc	0.06^b
中玉335 Zhongyu 335			3.84^bc	4.34^b	4.64^a	2.10^a	0.15^c	0.11^a
高油958 Gaoyou 858			3.93^a	3.20^c	3.21^b	1.76^a	0.47^a	0.08^b
中农787 Zhongnong 787			3.86^b	3.93^b	3.97^ab	1.75^a	0.42^ab	0.07^b
种植密度平均值 Mean of planting density
高 High			3.84	4.31	3.88	1.68	0.21^b	0.07^b
低 Low			3.87	4.01	3.57	1.63	0.44^a	0.09^a
添加剂平均值 Mean of additives
CK			3.85	4.19	3.71	1.54	0.33	0.09
LB			3.86	4.13	3.75	1.77	0.35	0.08
差异显著性 Significance of difference
品种 Variety			***	***	*	**	***	***
种植密度 Planting density			NS	NS	NS	NS	***	*
添加剂 Additive			NS	NS	NS	NS	NS	NS
品种×种植密度 Variety×planting density			*	*	**	*	**	NS
品种×添加剂 Variety×additive			NS	NS	NS	NS	NS	NS
种植密度×添加剂 Planting density×additive			NS	NS	NS	NS	NS	NS
品种×种植密度×添加剂 Variety×planting density×additive			NS	NS	NS	NS	***	*

同列数据肩标不同小写字母表示差异显著(P<0.05),相同小写字母或无字母表示差异不显著(P>0.05)。高密度:8.25×10⁴株/hm²;低密度:6.75×10⁴株/hm²;CK:无添加剂;LB:添加布氏乳杆菌。“*”、“**”和“***”分别表示P<0.05、P<0.01和P<0.001,“NS”表示P>0.05。下表同。

Values in the same column with different lowercase letter superscripts indicated significant differences (P<0.05), while with the same lowercase letter or no letter superscripts indicated no significant differences (P>0.05). High density: 8.25×10⁴ plants/hm²; low density: 6.75×10⁴ plants/hm²; CK: no additive; LB: adding Lactobacillus buchneri. “*”, “**” and “***” mean P<0.05, P<0.01 and P<0.001, and “NS” indicated P>0.05, respectively. The same as below.

2.2 品种、种植密度和添加剂对全株玉米青贮营养成分和体外消化率的影响

由表2可知,品种对全株玉米青贮营养成分含量均有显著影响(P<0.05)。“大康205”青贮的DM(“高油958”除外)和ST含量显著高于其他品种(P<0.05),NDF和ADF含量最低,显著低于“中玉335”青贮(P<0.05);“高油958”的营养品质次于“大康205”,“中玉335”的营养品质较差。从种植密度平均值来看,8.25×10⁴株/hm²种植密度全株玉米青贮营养品质优于6.75×10⁴株/hm²种植密度。从添加剂平均值来看,与无添加剂相比,添加布氏乳杆菌的全株玉米青贮DM和ST含量较高,NDF和ADF含量较低,表明添加布氏乳杆菌后青贮营养品质得到提升。此外,品种和种植密度对全株玉米青贮的DM、NDF和ADF含量有显著交互作用(P<0.05),品种和添加剂对ST含量有显著交互作用(P<0.05),品种、种植密度和添加剂对DM含量有显著交互作用(P<0.05)。

表2 品种、种植密度和添加剂全株玉米青贮的营养成分和体外消化率的影响

Table 2 Effects of varieties, planting density and additives on nutrients and in vitro digestibility of whole corn silage

品种 Varieties	种植密度 Planting density	添加剂 Additives	干物质 DM/ (% FM)	中性洗涤纤维 NDF/ (% DM)	酸性洗涤纤维 ADF/ (% DM)	可溶性碳水化合物 WSC/ (% DM)	淀粉 ST/ (% DM)	体外干物质消化率 IVDMD/ (% DM)	体外中性洗涤纤维消化率 IVNDFD/ (% DM)
大康205 Dakang 205	高 High	CK	32.86^bc	34.25^cd	18.77^cd	0.42^b	29.51^bc	34.25^d	20.79^abcd
		LB	34.64^ab	31.04^d	13.13^e	0.48^b	30.69^ab	31.04^d	29.09^a
	低 Low	CK	32.89^bc	36.22^cd	20.28^bcd	0.52^b	29.11^bc	36.22^d	19.21^abcde
		LB	33.93^ab	32.68^cd	17.88^cd	0.39^b	35.18^a	32.68^d	17.68^bcde
中玉335 Zhongyu 335	高 High	CK	24.84^e	43.32^ab	25.88^a	0.54^b	21.25^defg	43.32^c	24.45^abc
		LB	24.54^e	46.53^a	28.02^a	0.65^b	19.83^defg	46.53^c	20.43^abcd
	低 Low	CK	27.62^d	47.01^a	27.91^a	1.23^a	15.00^g	47.01^c	26.41^ab
		LB	28.34^d	45.43^a	26.77^a	0.79^b	16.14^g	45.43^c	20.36^abcd
高油958 Gaoyou 858	高 High	CK	30.80^c	38.10^bc	21.26^bc	0.58^b	24.87^cdef	53.71^b	14.90^cde
		LB	33.39^ab	32.32^cd	18.23^cd	0.56^b	26.31^cd	56.63^ab	16.53^e
	低 Low	CK	35.43^a	34.25^cd	18.56^cd	0.59^b	26.05^cde	58.28^ab	12.13^de
		LB	32.92^bc	36.71^cd	20.20^bcd	0.58^b	23.60^cdef	58.04^ab	15.86^bcde
中农787 Zhongnong 787	高 High	CK	32.91^bc	35.34^cd	18.68^cd	0.65^b	25.17^cde	57.26^ab	17.69^bcde
		LB	35.08^ab	31.31^d	16.25^de	0.51^b	17.66^fg	61.99^a	19.75^abcde
	低 Low	CK	25.22^e	43.33^ab	24.06^ab	0.63^b	15.87^g	53.47^b	17.13^bcde
		LB	26.32^de	43.33^ab	25.80^a	0.46^b	18.82^efg	53.74^b	19.32^abcde
标准差 SD			0.16	0.76	0.43	0.01	0.16	3.46	1.60
品种平均值 Mean of varieties
大康205 Dakang 205			33.58^a	33.55^c	17.52^c	0.45^b	33.62^a	33.55^c	21.69^ab
中玉335 Zhongyu 335			26.17^c	45.59^a	27.18^a	0.80^a	18.23^c	45.59^b	23.14^a
高油958 Gaoyou 858			33.14^a	35.35^bc	19.56^bc	0.58^b	25.21^b	56.66^a	12.86^b
中农787 Zhongnong 787			29.88^b	38.33^bc	21.20^bc	0.56^b	19.38^c	56.61^a	18.48^b
种植密度平均值 Mean of planting density
高 High			31.13^a	36.53^b	20.03^b	0.55	25.66^a	47.94	19.09
低 Low			30.42^b	39.63^a	22.50^a	0.64	22.75^b	48.38	18.81
添加剂平均值 Mean of additive
CK			30.32^b	38.98	21.93	0.65	23.35	48.09	19.45
LB			31.27^a	37.07	20.52	0.54	25.15	48.23	18.43
差异显著性 Significance of difference
品种 Variety			***	***	***	**	***	***	**
种植密度 Planting density			*	**	***	NS	**	NS	NS
添加剂 Additive			*	NS	NS	NS	NS	NS	NS
品种×种植密度 Variety×planting density			***	**	**	NS	NS	*	NS
品种×添加剂 Variety×additive			NS	NS	NS	NS	**	NS	NS
种植密度×添加剂 Planting density×additive			NS	NS	NS	NS	NS	NS	NS
品种×种植密度×添加剂 Variety×planting density×additive			*	NS	NS	NS	NS	NS	NS

品种对全株玉米青贮体外消化率有显著影响(P<0.05)。“高油958”青贮的IVDMD最高,显著高于“大康205”和“中玉335”(P<0.05);“大康205”的IVDMD最低,显著低于其他品种(P<0.05)。“中玉335”的IVNDFD显著高于“高油958”和“中农787”(P<0.05)。品种、种植密度和添加剂相互之间对全株玉米青贮体外消化率均无显著交互作用(P>0.05)。

2.3 全株玉米青贮发酵品质与营养成分的相关性分析

如图1所示,全株玉米青贮NDF和ADF含量与LA、AA、WSC和BA含量呈显著正相关(P<0.05);NH₃-N含量与pH和IVDMD呈显著负相关(P<0.05),IVDMD与IVNDFD和ST含量呈显著负相关(P<0.05),IVDMD与pH呈显著正相关(P<0.05),LA含量与AA含量呈显著正相关(P<0.05)。

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图1 全株玉米青贮发酵品质与营养成分的相关性

IVNDFD:体外中性洗涤纤维消化率 in vitro neutral detergent fiber digestibility;NH₃-N:氨态氮 ammonia nitrogen;ST:淀粉 starch;PA:丙酸 propionic acid;IVDMD:体外干物质消化率 in vitro dry matter digestibility;LA:乳酸 lactic acid;AA:乙酸 acetic acid;WSC:可溶性碳水化合物 water soluble carbohydrate;BA:丁酸 butyric acid;NDF:中性洗涤纤维 neutral detergent fiber;ADF:酸性洗涤纤维 acid detergent fiber。

“*”、“**”和“***”分别表示P<0.05、P<0.01和P<0.001。“*”, “**” and “***” mean P<0.05, P<0.01 and P<0.001, respectively.

Fig.1 Correlation between fermentation quality and nutrients of whole corn silage

3 讨论

3.1 全株玉米青贮发酵品质

玉米青贮的发酵参数,如pH、挥发性脂肪酸含量和氨水平,会影响奶牛的能量摄入^[17]。本研究中,各品种的全株玉米青贮pH都低于4.0,表明全株玉米都得到充分的发酵^[4]。Kung等^[18]研究发现,玉米青贮的pH在3.7~4.0,这与本研究一致。青贮期间蛋白质降解是不可避免的^[1],NH₃-N是比较准确的蛋白质水解指标,反映了氨基酸或肽的脱氨作用^[19]。本研究中,“高油958”青贮的NH₃-N含量显著低于其他品种,说明该品种玉米蛋白质降解较少;同时,“高油958”青贮AA含量显著高于“大康205”。在优质的青贮中丁酸含量一般都处于低浓度或者不会检出^[5],本研究中各处理青贮丁酸含量较低。

3.2 全株玉米青贮营养成分和体外消化率以及相关性分析

全株玉米青贮拥有玉米籽粒,可有效保存全株玉米营养成分,并提高经济效益^[20]。DM含量反映了全株玉米青贮的营养价值,也决定了青贮饲料的经济效益^[21]。本试验的“大康205”青贮DM含量最高(33.58%),其次是“高油958”(33.14%)。有研究表明,玉米青贮的DM含量在30%~35%时可以改善奶牛的产奶量^[22],说明本研究的玉米青贮DM含量在合理范围内。本研究中4个品种玉米青贮的ST含量存在显著差异,其中添加布氏乳杆菌的“大康205”品种在6.75×10⁴株/hm²的种植密度下ST含量最高,可达35.18%。造成这种差异的原因可能是不同品种玉米的籽粒占全株比重不同,导致玉米全株的ST含量不同^[23]。IVDMD会随着木质化和细胞壁厚度的增加而降低^[24],本研究中“高油958”青贮的IVDMD最高,这是由于“高油958”品种玉米籽粒中的CP和ST含量较高^[25],所以其木质化程度较低。有研究表明,玉米青贮的营养价值与NDF和ADF含量呈负相关,与CP、粗脂肪、钙和磷含量呈正相关^[26]。本研究中,全株玉米青贮ST含量与NDF和ADF含量呈负相关,NDF含量与ADF含量呈显著正相关,这与王瑛等^[27]的研究结果一致,说明ST含量越高,NDF和ADF含量越低。同时,全株玉米青贮WSC含量与LA和PA含量呈负相关,这可能是由于WSC作为青贮发酵过程中被乳酸菌直接利用的发酵底物^[28],消耗的WSC越多,产生的LA和PA就越多。

3.3 种植密度对全株玉米青贮营养价值的影响

本研究中,高种植密度(8.25×10⁴株/hm²)全株玉米青贮的营养品质优于低种植密度(6.75×10⁴株/hm²),且种植密度对青贮NDF、ADF和ST含量有显著影响。研究表明,高种植密度可以显著提高玉米的营养品质^[29]。本研究中,高种植密度全株玉米青贮后的NDF和ADF含量显著低于低种植密度。王瑛等^[27]在甘肃庆阳研究同一品种不同种植密度玉米青贮营养品质发现,高种植密度(6.00×10⁴和6.75×10⁴株/hm²)玉米青贮的NDF和ADF含量显著低于低种植密度(4.50×10⁴和5.25×10⁴株/hm²),这与本研究结果一致。但也有研究表明,高种植密度导致籽粒和秸秆中纤维含量提高,CP含量降低,从而引起全株玉米中的可消化组分含量降低,饲用价值下降^[30]。

3.4 收获时间对全株玉米青贮营养价值的影响

受通辽地区当年收获时间天气的影响,本研究中“大康205”和“高油958”品种玉米都于蜡熟期收获,而“中玉335”和“中农787”品种玉米由于其生育周期长收获时处于乳熟期。乳熟期全株玉米DM含量较低,青贮时易产生梭菌,从而降低青贮后的营养品质。而蜡熟期青贮的全株玉米饲料营养价值较高,奶牛在饲喂蜡熟期玉米青贮后其乳蛋白含量提高^[31]。所以本研究中蜡熟期收获的“大康205”和“高油958”品种玉米的青贮品质优于乳熟期收获的“中玉335”和“中农787”品种玉米。张晓驰等^[32]认为,不同生育时期全株玉米青贮的NDF和ADF含量为乳熟期>完熟期>蜡熟期,且蜡熟期瘤胃降解率最高,与本研究结果一致。

4 结论

本研究中,各玉米品种在青贮后适应性差异较大,“大康205”和“高油958”品种玉米的青贮品质较好,高种植密度(8.25×10⁴株/hm²)的全株玉米青贮营养成分更高,添加布氏乳杆菌可提高全株玉米青贮发酵品质;综合评价得出,“高油958”适宜在通辽地区作为青贮玉米推广种植。

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