我国南方地区发展草食畜牧业具有得天独厚的自然条件优势。草食畜牧业生产体系能够有效地解决畜牧业发展过程中带来的“人畜争粮”矛盾，推进农业结构调整。牛羊等反刍动物养殖业作为发展草食畜牧业的主要源动力需要全年优质饲草料供给。甜高粱（Sorghum bicolor (L.) Moench）是禾本科C4<下标!>植物，适宜在我国南方地区种植，其糖分含量高，蛋白质含量低，易于青贮。紫花苜蓿（Medicago sativa L.）是豆科牧草，蛋白质含量丰富，营养价值高，但水溶性碳水化合物含量低，缓冲能高，常规青贮难以成功。将甜高粱和紫花苜蓿按一定比例进行混合青贮，可以获得优质青贮饲料，满足反刍动物生产全年优质饲草料的供应。本研究旨在探讨甜高粱和紫花苜蓿不同混合比例对青贮发酵品质、有氧稳定性和体外瘤胃发酵特性的影响，筛选出适宜的混合青贮比例，在此基础上进一步添加同/异质型复合乳酸菌和纤维素酶对其发酵品质、有氧稳定性和体外瘤胃发酵特性进行调控，为当地甜高粱和紫花苜蓿混合青贮饲料的生产提供理论依据。本论文主要分为以下六个部分： 试验一 甜高粱和紫花苜蓿不同混合比例对青贮发酵品质和瘤胃养分降解率的影响 本试验旨在研究甜高粱和紫花苜蓿不同混合比例对青贮发酵品质和瘤胃养分降解率的影响。试验共设5个处理：（1）100% 甜高粱 + 0%紫花苜蓿（SA0）；（2）75%甜高粱 + 25%紫花苜蓿（SA25）；（3）50%甜高粱 + 50%紫花苜蓿（SA50）；（4）25%甜高粱 + 75%紫花苜蓿（SA75）；（5）0%甜高粱 + 100%紫花苜蓿（SA100），每个处理6个重复。青贮45天开窖取样，分析化学和营养成分，评价青贮发酵品质，并进一步通过尼龙袋法研究青贮饲料干物质（DM）、粗蛋白（CP）、中性洗涤纤维（NDF）和酸性洗涤纤维（ADF）的瘤胃降解特性。结果表明：随着紫花苜蓿在混合青贮饲料中比例的增加，异型发酵逐渐增强，干物质回收率、乳酸含量和乳酸/乙酸值呈线性趋势降低（P < 0.05），而pH值和乙酸含量呈线性趋势增加（P < 0.05）。随着紫花苜蓿在混合青贮饲料中比例的增加，梭菌发酵逐渐增强，丁酸和氨态氮（NH3-N）含量以及梭菌孢子数量呈线性趋势增加（P < 0.05）。随着紫花苜蓿在混合青贮饲料中比例的增加，CP含量呈线性趋势升高（P < 0.05），但与青贮前各处理组原料相比，SA50、SA75和SA100处理组CP损失程度高于SA0和SA25处理组。青贮饲料DM和CP有效降解率随着紫花苜蓿在混合青贮饲料中比例的增加呈线性趋势增加（P < 0.05），而NDF和ADF有效降解率呈线性趋势降低（P < 0.05）。综合考虑混合青贮的发酵品质和营养价值，得出结论为75%甜高粱 + 25%紫花苜蓿为适宜混合青贮比例。 试验二 甜高粱和紫花苜蓿不同混合比例对青贮饲料有氧稳定性的影响 本试验旨在研究甜高粱和紫花苜蓿不同混合比例对青贮饲料有氧稳定性的影响。试验共设5个处理：（1）SA0；（2）SA25；（3）SA50；（4）SA75；（5）SA100，每个处理6个重复。青贮45天打开青贮窖，取出青贮饲料并将其混合均匀后，分别装入对应的2 L聚乙烯塑料瓶中，用于测定青贮饲料有氧稳定性，分别在有氧暴露第0、3、5和7 d取样测定pH值、NH3-N含量、乳酸菌、酵母菌、霉菌和梭菌孢子数量的变化，以及有氧暴露第7 d的化学成分含量。结果表明：青贮饲料有氧稳定性随着紫花苜蓿在混合青贮饲料中比例的增加呈线性趋势升高（P < 0.05）。SA0、SA25、SA50、SA75和SA100处理组有氧稳定性分别为69.7、80.0、99.5、>168和>168 h。所有处理组pH值、NH3-N含量、酵母菌、霉菌和梭菌孢子数量均随着有氧暴露时间的延长而逐渐升高（P < 0.05），而乳酸菌数量则逐渐降低。在有氧暴露阶段，pH值、NH3-N含量、酵母菌、霉菌和梭菌孢子数量上升的速度随着紫花苜蓿在混合青贮饲料中比例的增加而逐渐降低。和青贮发酵45 d时的各处理组相比，有氧暴露第7 d时的各处理组DM、水溶性碳水化合物和CP含量降低，而其它化学成分含量均有所升高。根据以上结果得出，增加紫花苜蓿混合比例有益于提高混合青贮饲料的有氧稳定性，抑制酵母菌、霉菌和梭菌孢子的生长。 试验三 甜高粱和紫花苜蓿不同混合比例对青贮饲料体外瘤胃发酵特性的影响 本试验旨在研究甜高粱和紫花苜蓿不同混合比例对青贮饲料体外瘤胃发酵特性的影响。试验共设5个处理：（1）SA0；（2）SA25；（3）SA50；（4）SA75；（5）SA100，每个处理6个重复。以发酵45 d的青贮饲料为试验材料，采用体外产气法测定其体外发酵48 h发酵液的产气量、甲烷产量、养分降解率、微生物酶活性、发酵参数、微生物蛋白（MCP）浓度以及纤维和蛋白分解菌相对数量。结果表明：随着紫花苜蓿在混合青贮饲料中比例的增加，体外发酵48 h发酵液的产气量、体外NDF降解率（IVNDFD）、羧甲基纤维素酶、纤维二糖酶和木聚糖酶活性、短链脂肪酸（SCFA）浓度、丙酸摩尔比例、MCP浓度、产琥珀酸丝状杆菌和黄色瘤胃球菌数量呈先升高后降低线性趋势变化（P < 0.05）；甲烷产量、NH3-N浓度、乙酸摩尔比例和乙酸/丙酸呈先降低后升高线性趋势变化（P < 0.05）；体外DM降解率（IVDMD）、体外CP降解率（IVCPD）、蛋白酶活性、pH值、异丁酸、戊酸和异戊酸摩尔比例、普雷沃式菌数量呈线性趋势升高（P < 0.05）；体外ADF降解率（IVADFD）、α-淀粉酶活性、丁酸摩尔比例、溶纤维丁酸弧菌和嗜淀粉瘤胃杆菌数量呈线性趋势降低（P < 0.05）。和其它处理组相比，SA25处理组体外发酵48 h产气量、IVNDFD、羧甲基纤维素酶、纤维二糖酶和木聚糖酶的活性、SCFA和MCP浓度、产琥珀酸丝状杆菌和黄色瘤胃球菌数量最高，而乙酸/丙酸和甲烷产量最低。根据以上结果得出，在相同条件下饲喂SA25处理组有利于提高瘤胃MCP的合成量，减少瘤胃甲烷对环境的污染，促进反刍动物对能量和氮的利用。 试验四 添加剂对甜高粱和紫花苜蓿混合青贮发酵品质和瘤胃养分降解率的影响 本试验旨在研究添加剂对甜高粱和紫花苜蓿混合青贮发酵品质和瘤胃养分降解率的影响。以75%甜高粱 + 25%紫花苜蓿为青贮原料，共设4个处理组：（1）对照组（Control）；（2）乳酸菌组（LAB）；（3）纤维素酶组（E）；（4）乳酸菌 + 纤维素酶组（LE），每个处理6个重复。青贮45天开窖取样，测定化学和营养成分，评价青贮发酵品质，并进一步通过尼龙袋法研究混合青贮饲料DM、CP、NDF和ADF的瘤胃降解特性。结果表明：添加LAB和E均能改善混合青贮饲料的发酵品质，显著提高了干物质回收率和乳酸含量（P < 0.05），显著降低了pH值和NH3-N含量（P < 0.05），但LAB和LE处理组乙酸含量显著高于对照组（P < 0.05）。添加LAB和E显著提高了真蛋白含量（P < 0.05），显著降低了非蛋白氮和可溶性蛋白含量（P < 0.05）。添加E显著降低了NDF和ADF含量（P < 0.05），显著增加了水溶性碳水化合物含量（P < 0.05）。LAB和E对改善混合青贮发酵品质存在协同性作用（P < 0.05），添加LE能够进一步提高干物质回收率和乳酸含量，降低pH值和NH3-N含量。添加LAB和E均显著提高了混合青贮饲料DM和CP有效降解率（P < 0.05），而对NDF和ADF有效降解率没有显著影响（P > 0.05）。根据以上结果得出，甜高粱和紫花苜蓿混合青贮时添加LE能最大程度地降低蛋白质降解，提高发酵品质，获得最优质的青贮饲料。 试验五 添加剂对甜高粱和紫花苜蓿混合青贮饲料有氧稳定性的影响 本试验旨在研究添加剂对甜高粱和紫花苜蓿混合青贮饲料有氧稳定性的影响。以75%甜高粱 + 25%紫花苜蓿为青贮原料，共设4个处理组：（1）对照组；（2）LAB；（3）E；（4）LE，每个处理6个重复。青贮45天打开青贮窖，取出青贮饲料并将其混合均匀后，分别装入对应的2 L聚乙烯塑料瓶中，用于测定混合青贮饲料有氧稳定性，分别在有氧暴露第0、3、5和7 d取样评定其pH值、NH3-N含量、乳酸菌、酵母菌、霉菌和梭菌孢子数量的变化，以及有氧暴露第7 d的化学成分含量。结果表明：添加剂对混合青贮饲料有氧稳定性具有显著影响（P < 0.05）。对照组、LAB、E和LE处理组有氧稳定性分别为80.0、91.2、70.0和90.3 h。在有氧暴露阶段，与对照组相比，LAB和LE处理组pH值、NH3-N含量、酵母菌、霉菌和梭菌孢子数量增长较慢，而E处理组pH值、NH3-N含量、酵母菌、霉菌和梭菌孢子数量增长较快。有氧暴露第7 d时，LAB和LE处理组非蛋白氮和可溶性蛋白含量显著低于对照组（P < 0.05），而E处理组非蛋白氮和可溶性蛋白含量显著高于对照组（P < 0.05）。根据以上结果得出，添加LAB提高了混合青贮饲料的有氧稳定性，降低了混合青贮饲料有氧暴露期间的蛋白质分解程度；而添加E降低了混合青贮饲料的有氧稳定性，增加了混合青贮饲料有氧暴露期间的蛋白质分解程度。 试验六 添加剂对甜高粱和紫花苜蓿混合青贮饲料体外瘤胃发酵特性的影响 本试验旨在研究添加剂对甜高粱和紫花苜蓿混合青贮饲料体外瘤胃发酵特性的影响。以75%甜高粱 + 25%紫花苜蓿为青贮原料，共设4个处理组：（1）对照组；（2）LAB；（3）E；（4）LE，每个处理6个重复。以发酵45 d的青贮饲料为试验材料，采用体外产气法测定添加剂处理的混合青贮饲料体外发酵48 h发酵液的产气量、养分降解率、微生物酶活性、发酵参数、MCP浓度以及纤维和蛋白分解菌相对数量。结果表明：添加LAB和E均能影响瘤胃发酵效率。LAB、E和LE处理组发酵液的IVDMD、IVCPD、蛋白酶活性、MCP浓度和普雷沃式菌相对数量显著高于对照组（P < 0.05），且LE处理组IVDMD、IVCPD、蛋白酶活性、MCP浓度和普雷沃式菌相对数量最高；而乙酸/丙酸和甲烷产量显著低于对照组（P < 0.05），且LE处理组乙酸/丙酸和甲烷产量最低。根据以上结果得出，添加剂提高了混合青贮饲料的瘤胃发酵效率，这与其促进了瘤胃普雷沃式菌的生长有关，其中LE处理组对提高微生物蛋白合成量和降低甲烷产量效果最好。 综合评价甜高粱和紫花苜蓿不同混合比例对青贮发酵品质、有氧稳定性以及体外瘤胃发酵特性的影响，以75%甜高粱 + 25%紫花苜蓿混合青贮效果最优；不同添加剂对甜高粱和紫花苜蓿混合青贮饲料发酵品质、有氧稳定性以及体外瘤胃发酵特性的改善效果，乳酸菌和纤维素酶组合添加效果最佳。

There are favorable natural advantages of developing herbivorous animal huabandry in Southern China, which can effectively solve the contradiction of human food versus animal feed competition, and promote agricultural structure regulation. Ruminant animal production such as cattle and sheep, the main driving force of development of herbivorous animal husbandry, is required to be supplied with year-around high quality forages. Sweet sorghum (Sorghum bicolor (L.) Moench; SS) belongs to C4<下标!> plant with high sugar contents and low crude protein contents, which collectively characterizes it to be ensiled well. Alfalfa (Medicago sativa L.; AF) belongs to legume with high nutritive value, is rich in crude protein, however, it is difficult to ensile due to low water soluble carbohydrates contents and high buffering capacity. High qulaity silages can be produced with ensiling SS and AF in certain proportions, which would meet the requirement of year-around high quality forages for ruminant animal production. Therefore, the first objective of this study was to evaluate the effect of ensiling SS with AF in different ratios on the fermentation quality, aerobic stability and in vitro ruminal fermenatation characteristics of silages, and then to select a best mixing ratio for SS-AF silage production. On the basis of the best mixing ratio of SS and AF for SS-AF silage production, the second objective was to determine if the addition of homofermentative/heterfermentative lactic acid bacteria mixtures and fibrolytic enzymes would enhance the fermentation quality, aerobic stability and in vitro ruminal fermenatation characteristics of SS-AF silages. The data obtained in this study can supply theoretical basis for the practical production of SS-AF silages in Southern China. This study consisted of the following six experiments: Experiment 1. The effect of different mixing ratios of sweet sorghum to alfalfa on the fermentation quality and ruminal nutrient degradability of silages The objective of this experiment was to determine the effect of different mixing ratios of SS to AF on the fermentation quality and ruminal nutrient degradability of silages. Five experimental treatments varying in the ratio of SS to AF: 100:0 (SA0), 75:25 (SA25), 50:50 (SA50), 25:75 (SA75) and 0:100 (SA100) on a fresh matter basis were prepared. All experimental treatments were ensiled for 45 d in laboratory silos (six silo replicates per treatment), after which silage samples were taken to evaluate the fermeantation quality with measuring the chemical and nutritive composition. Further, the experimental silages were subjected to an in situ nylon bag experiment to evaluate the kinetics of ruminal degradability of dry matter (DM), crude protein (CP), neutral detergent fiber (NDF) and acid detergent fiber (ADF). The results showed that the heterofermentation enhanced with increasing proportion of AF in the SS-AF silages, as indicated by the fact that DM recovery, lactic acid contents and lactic acid to acetic acid ratios linearly decreased (P < 0.05), while pH and acetic acid contents, linearly increased (P < 0.05). Moreover, increasing proportion of AF in the SS-AF silages also enhanced clostridial fermentation, as indicated by the fact that butyric acid and ammonia nitrogen (NH3-N) contents as well as clostriadia spore counts linearly decreased (P < 0.05). The CP contents linearly increased (P < 0.05) with increasing proportion of AF in the silages, however, compared to the pre-ensiled forages of each treatment group, the CP loss was higher in SA50, SA75 and SA100 silages than SA0 and SA25 silages. The effective degradability (ED) of DM and CP linearly increased (P < 0.05) with increasing proportion of AF in the silages, while the ED of NDF and ADF linearly decreased (P < 0.05). The results obtained in this experiment indicated that the ratio of SS to AF of 75:25 was the most suitable for silage production considering the fermentation quality and nutritive value of mixed silages. Experiment 2. The effect of different mixing ratios of sweet sorghum to alfalfa on the aerobic stability of silages The objective of this experiment was to determine the effect of different mixing ratios of SS to AF on the aerobic stability of silages. Five experimental treatments varying in the ratio of SS to AF: SA0, SA25, SA50, SA75 and SA100 on a fresh matter basis were prepared. All experimental treatments were ensiled for 45 d in laboratory silos (six silo replicates per treatment), after which silage samples were collected and mixed homogeneously, and placed into a polyethylene plastic bottle (2 L capacity) to detecte the aerobic stability of silage, and then to evaluate the changes of the pH value, NH3-N content, and lactic acid bacteria, yeast, mould and clostridia spore counts of air-exposed silages at the 0th, 3th, 5th and 7th d. In addition, the chemical composition of air-exposed silages at the 7th d was also analysed. The results showed that the aerobic stability linearly increased (P < 0.05) with the increasing proportion of AF in the silages. The aerobic stability of SA0, SA25, SA50, SA75 and SA100 silage was 69.7, 80.0, 99.5, >168 and >168 h, respectively. The pH value, NH3-N content, and lactic acid bacteria, yeast, mould and clostridia spore counts of all silages gradually increased (P < 0.05) with the time of air exposure, and these parameters increased more rapidly in SA0, SA25 and SA50 silages than SA75 and SA100 silages. Compared to the silages with different treatments at 45 d, the DM, water soluble carbohydrates and CP contents of the air-exposed silages with different treatments at 7th d decreased, while other chemical compositions increased. The results obtained in this experiment indicated that increasing proportion of AF in the SS-AF silages is benefit of improving the aerobic stability of mixed silages, and inhibiting the growth of yeasts, moulds and clostridia spores. Experiment 3. The effect of different mixing ratios of sweet sorghum to alfalfa on the in vitro ruminal fermentation characteristics of silages The objective of this study was to determine the effect of different mixing ratios of SS to AF on the in vitro ruminal fermentation characteristics of silages. Five experimental treatments varying in the ratio of SS to AF: SA0, SA25, SA50, SA75 and SA100 on a fresh matter basis were prepared. All experimental treatments were ensiled for 45 d in laboratory silos (six silo replicates per treatment). The gas production, methane production, nutrient degradability, microbial enzyme activity, fermentation parameters, microbial protein (MCP) concentration and relative populations of cellulolytic and proteolytic bacteria of the five experimental silages after 48 h in vitro fermentation were determined with the in vitro gas technique. The result showed the gas production, in vitro NDF degradability (IVNDFD), activity of carboxymethyl cellulose, cellobiase and xylanase, short-chain fatty acids (SCFA), propionic acid molar proportion, MCP concentration, relative quantity of Fibrobacter succinogenes and Ruminococcus flavefaciens linearly increased and then decrease (P < 0.05) with increasing proportion of AF in the SS-AF silages after in vitro inoculation for 48 h; the methane production, NH3-N concentration, acetic acid molar proportion and ratio of acetic acid to propionic acid linearly decreased and then increased (P < 0.05); the in vitro DM degradability (IVDMD), in vitro CP degradability (IVCPD), activity of protease, pH, molar proportion of isovaleric acid, valeric acid and isobutyric acid, relative quantity of genus Prevotella linearly increased (P < 0.05); the in vitro ADF degradability (IVADFD), activity of α-amylase, butyric acid molar proportion, relative quantity of Butyrivibrio fibrisolvens and Ruminobacter amylophilus linearly decreased (P < 0.05). Compared to other silages, SA25 treatment had the highest the gas production after in vitro inoculation for 48 h, IVNDFD, activity of carboxymethyl cellulose, cellobiase and xylanase, SCFA and MCP concentrations, and relative quantity of Fibrobacter succinogenes and Ruminococcus flavefaciens, and the lowest ratio of acetic acid to propionic acid and methane production. The results obtained in this experiment indictaed that SA25 silage is a relative energy and nitrogen balance, under the same conditions of usage, there could be benefits for increasing MCP synthesis and reducing excretion to the environment, and facilitating the use of energy and nitrogen by ruminat animals with SA25 silage rather than other silages. Experiment 4. The effect of additives on the fermentation quality and ruminal nutrient degradability of sweet sorghum-alfalfa silages The objective of this experiment was to determine the effect of additives on the quality and ruminal nutrient degradability of SS-AF silages. The mixture of 75% SS + 25% AF was chose as the ensiling material. Four experimental treatments were prepared: (1) no additives (Control); (2) lactic acid bacteria (LAB); (3) fibrolytic enzymes (E); (4) lactic acid bacteria + fibrolytic enzymes (LE). All experimental treatments were ensiled for 45 d in laboratory silos (six silo replicates per treatment), after which silage samples were taken to evaluate the fermeantation quality with measuring the chemical and nutritive composition. Further, the experimental silages were subjected to an in situ nylon bag experiment to evaluate kinetics of ruminal degradability of DM, CP, NDF and ADF. The results showed that LAB and E addition improved the fermentation quality of SS-AF silages, as indicated by higher (P < 0.05) DM recovery and lactic acid contents, lower (P < 0.05) pH values and NH3-N contents, however, LAB and LE silages had higher acetic acid contents than the Control silage. LAB and E addition had significant effects on increasing the true protein contents, and decreasing non-protein nitrogen and soluble protein contents. E and IE addition decreased (P < 0.05) the NDF and ADF contents, while increased (P < 0.05) water soluble carbohydrates contents. LAB and E showed a supplemental effect on the fermentation quality of SS-AF silages, and LE addition further increased the DM recovery and lactic acid content of SS-AF silages, and decreased the pH and NH3-N content. Compared to the Control, LAB, E and LE addition improved (P < 0.05) the ED of DM and CP, while had no effects (P > 0.05) on the ED of NDF and ADF. The results indicated that LE addition at ensiling can to the greatest extent reduce proteolysis and improve fermentation quality of SS-AF silages, thus, achieving the best quality silage. Experiment 5. The effect of additives on the aerobic stability of sweet sorghum-alfalfa silages The objective of this experiment was to determine the effect of additives on the aerobic stability of SS-AF silages. The mixture of 75% SS + 25% AF was chose as the ensiling material. Four experimental treatments were prepared: (1) Control; (2) LAB; (3) E; (4) LE. All experimental treatments were ensiled for 45 d in laboratory silos (six silo replicates per treatment), after which silage samples were collected and mixed homogeneously, and placed into a polyethylene plastic bottle (2 L capacity) to detect the aerobic stability of the silages, and then to evaluate the changes of the pH value, NH3-N content, and lactic acid bacteria, yeast, mould and clostridia spore counts of air-exposed silages at the 0th, 3th, 5th and 7th d. In addition, the chemical composition of air-exposed silages at the 7th d was also analysed. The results showed that additives had a significant effect (P < 0.05) on the aerobic stability of SS-AF silages. The aerobic stability of the Control, LAB, E and LE silages was 80.0, 70.0, 91.2 and 90.3 h, respectively. Compared to the Control, E addition accelerated the elevation of the pH value, NH3-N content, and yeast, mould and clostridia counts of SS-AF silages during air exposure, while LAB addition slowered the elevation of the pH value, NH3-N content, and yeast, mould and clostridia spore counts during air exposure. the non-protein nitrogen and soluble protein contents of air-exposed silages at 7th d were higher (P < 0.05) in LAB and LE silages than the Control silage, while were lower (P < 0.05) in E silage. The results obtained in this experiment indicated that LAB addition improved the aerobic stability of SS-AF silages and decreased the extent of proteolysis, while E addition decreased the aerobic stability and increased the extent of proteolysis.