优质甜高粱与苜蓿混合青贮的筛选及其形成机理研究

Alfalfa is one of leguminous plants, and it is difficult to be ensiled due to its high protein content, high buffering capacity, low dry matter and water soluble carbohydrate content. Sweet sorghum is a C4 plant which has high photosynthetic efficiency, high sugar content, high biological production and strong stress resistance. Theoretically, sweet sorghum can provide sugar to lactic acid bacteria during fermentation, while alfalfa can provide protein for the mixed forage silage. Therefore, ensiling of alfalfa with sweet sorghum may overcome some of their drawbacks respectively. As a result, better mixed forage silage with balanced energy and protein content may be produced. So far, there are little research have been done on ensiling of alfalfa with sweet sorghum in china or overseas. This research project will use alfalfa and selected sweet sorghum varieties that adapted to the extreme weather and geological conditions of Tarim Basin in our pre-experiment to make mixed silage in different proportion. Through silage chemical analysis, quality analysis, aerobic stability test, rumen fermentation experiments,and silage flora diversity analysis, the relationship between the proportion of alfalfa and sweet sorghum in the mix silage making and the silage quality, digestibility, superiority bacterium type will be determined.the proportion of sweet sorghu and alfalfa that could produce high-quality mixed silage will be selected. This research project is designed to select an appropriate proportion of alfalfa and sweet sorghum that could produce high-quality mixed silage, and to uncover the microbiological mechanisms of the proportion of sweet sorghum and alfalfa on the high-quality mixed silage. The results of the project can provide the scientific basis for developing new-type mixed silage, resolving the problems of forage with inadequate quality and quantity in south Xinjing, and promoting the regional development of animal husbandry economy.

苜蓿属豆科牧草，由于蛋白含量高、缓冲度高、可溶碳水化合物和干物质含量低，青贮难以成功。甜高粱属C4植物，光合效率高、糖含量高、生物产量大、抗逆性强。理论上讲，甜高粱可为青贮乳酸菌发酵提供糖分，苜蓿可为混合青贮提供蛋白质，二者混合青贮可克服各自缺陷，提高混合青贮饲料的能-蛋平衡。然而，国内外缺乏使用甜高粱与苜蓿进行混合青贮的研究报道。本项目以前期筛选的适应塔里木盆地极端气候和地质土壤条件的甜高粱品种和苜蓿为材料，制作不同比例的混合青贮饲料，通过营养成分分析、青贮品质分析、有氧稳定性检验、瘤胃发酵实验和青贮菌群多样性分析，比较混合比例与青贮饲料质量、优势菌群变化，以及可消化特性之间的关系，筛选优质混合青贮的混合比例，揭示优质甜高粱与苜蓿混合青贮特性形成的微生物学机制。该研究为制作甜高粱与苜蓿新型混合青贮饲料，解决南疆粗饲料"质"和"量"短缺的问题，促进区域畜牧经济发展提供科学依据。

为探讨甜高粱与苜蓿混贮的营养特性，项目以甜高粱和苜蓿为原料，按甜高粱与苜蓿比例为0:100（0%SS）、20:80（20%SS）、40:60 (40%SS)、60:40（60%SS）、80:20 (80%SS)和100:0 (100%SS)制作混贮，分析了混贮营养特性、细菌多样性、降解率和有氧稳定性，得出如下结果：.（1）添加少量甜高粱即可提高苜蓿青贮成功率，当甜高粱比例增加到40%，混贮成功率即可达到100%；混贮中粗蛋白、灰分、皂苷随甜高粱比例的增加而减少，可溶性糖、淀粉、单宁和粗纤维随甜高粱比例的增加而增加。（2）混贮中乳酸随甜高粱比例的增加而增加，NH3、pH、乙酸和丁酸则则显著下降；有氧稳定性随甜高粱比例的增加而下降，酵母菌、霉菌、好氧菌数量、pH值随有氧暴露时间的延长而增加，而乳酸菌数量则持续减少，酵母菌和好氧菌的数量随甜高粱比例的增加而显著上升，霉菌则显著减少。（3）混贮的瘤胃降解率、产气量、CH4、pH、NH3和VFA随甜高粱比例的减少而增加，0%SS、20%SS和40%SS的混贮瘤胃产气量、CH4和降解率显著高于80%SS和100%SS混贮，这说明甜高粱比例较低的混贮（0%SS、20%SS、40%SS）更有利于提高混贮的降解率。（4）从混贮中分离到了18株乳酸菌，20%SS、40%SS和60%SS混贮乳酸菌种类丰富，鼠李糖乳杆菌和屎肠球菌是0%SS、20%SS、40%SS、60%SS、80%SS混贮的优势乳酸菌。（5）在门水平分布而言，广古菌门是0%SS混贮的优势细菌，变形菌门是20%SS、40%SS、100%SS混贮的优势细菌，厚壁菌门是60%SS和80%SS混贮的优势细菌，而且厚壁菌门的相对丰度随甜高粱比例的增加而增高；进一步的分类结果表明，Methanomassiliicoccaceae是0%SS混贮的优势菌群（40.1%），变形菌纲是20%SS混贮的优势菌群（18.2%），假单胞菌属是40%SS和100SS%混贮的优势菌群（分别为26.6%和19.5%），芽孢杆菌科是60%SS混贮的优势菌群（21.7%），枝芽孢菌属是80%SS混贮的优势菌群（38.8%）（19.5）。.可见，甜高粱与苜蓿混贮可以提高青贮品质，有利于增加青贮细菌的多样性；综合青贮品质、有氧稳定性及降解率等指标，可以确定20%SS和40%SS为优质甜高粱与苜蓿混贮的最佳比例。