【作者】 李斌；

【导师】 刘德武； 郭勇庆；

【作者基本信息】 华南农业大学 ， 农业硕士（专业学位）， 2019， 硕士

【摘要】 牛奶中乳脂含量易受日粮影响,当日粮中精料比例或油脂比例过高时,会导致的乳脂含量降低,进而引发乳脂降低综合征（Milk Fat Depression,MFD）。高淀粉高油脂日粮导致的MFD是日粮营养成分与胃肠道微生物互作的直接结果,但目前在日粮导致MFD的条件下,奶牛胃肠道微生物区系的变化规律仍不清楚。为了探究日粮因素导致MFD条件下奶牛瘤胃和后肠道微生物的变化规律,进而挖掘MFD的发生机制,本试验选取了8头头胎荷斯坦奶牛作为试验动物,分为处理组和对照组,每组4头。试验采用了2×2反转试验设计,分为两期（每期为23d）,包括诱导期16d和恢复期7d。在诱导期,对照组奶牛饲喂含低淀粉低油脂的日粮（精粗比为50:50）,处理组奶牛饲喂高淀粉高油脂的日粮（在对照组日粮基础上添加266g/kg粉碎玉米和46g/kg大豆油,干物质基础）,以期诱导出MFD;在恢复期中所有牛只饲喂对照组日粮。在采样期采集所有牛奶、瘤胃液和粪便样品,检测其泌乳性能、瘤胃和后肠道发酵及细菌区系等指标的变化规律,为进一步探索日粮因素导致MFD的发生机制提供理论基础。试验结果表明:（1）在饲喂高淀粉高油脂日粮后,奶牛乳脂率降至2.87%（P<0.01）,表明奶牛成功诱导出现乳脂合成抑制;同时,处理组奶牛干物质采食量、产奶量、3.5%校正乳产量、能量校正乳产量、乳脂产量、乳蛋白产量、乳糖产量、非脂固体产量及饲料转化效率均显著低于对照组（P<0.05）。（2）在饲喂高淀粉高油脂日粮后,奶牛瘤胃液NH₃-N浓度及乙酸摩尔比均显著低于对照组（P<0.05）,但瘤胃液p H值以及乙酸、丙酸和丁酸浓度等挥发性脂肪酸浓度未受日粮影响。（3）根据瘤胃液细菌区系测序结果分析,拟杆菌门、厚壁菌门和变形菌门为优势菌门;在饲喂高淀粉高油脂日粮后,奶牛瘤胃中细菌区系出现显著变化,且细菌菌群的丰富度和多样性均显著降低;纤维杆菌门的相对丰度显著降低,而放线菌门的相对丰度显著上升;拟杆菌中多数菌属及与纤维降解相关菌属如Fibrobacter的相对丰度显著下降,而厚壁菌和放线菌中参与生物氢化途径的菌属如Lachnospiraceae、Butyrivibrio和Coriobacteriaceae的相对丰度显著上升。（4）在饲喂高淀粉高油脂日粮后,奶牛粪便p H值及乙酸摩尔比显著下降,丁酸摩尔比显著上升;从时间点曲线分析,处理组奶牛粪便中总挥发性脂肪酸浓度随采样时间点的延长有不断增加的趋势。（5）根据粪便细菌区系测序结果分析,拟杆菌门、厚壁菌门、放线菌门和变形菌门为优势菌门;在饲喂高淀粉高油脂日粮后,奶牛粪便中细菌区系出现显著变化,且细菌菌群的丰富度和多样性均显著降低;放线菌门和疣微菌门等相对丰度显著下降,而变形菌门的相对丰度则显著上升;Succinivibrio的相对丰度显著显著上升,而Ruminococcaceae和益生菌Bifidobacterium的相对丰度也显著降低。综上可知,饲喂高淀粉高油脂日粮可造成奶牛出现MFD,与此同时,奶牛瘤胃、后肠道的发酵活动及细菌区系的变化与日粮导致的MFD息息相关;本试验挖掘了一些与乳脂合成相关的菌群,对后续探究MFD发生机制的研究提供了一定的理论基础。更多还原

【Abstract】 Milk fat is easily affected by the diets in the milk of dairy cows.Feeding a high level of concentrate or oil diet could cause a reduction in milk fat yield in dairy cows,leading to Milk Fat Depression（MFD）.Diet-induced MFD in dairy cows is the direct consequence of gastrointestinal microbiota activity that is responsive to dietary nutrients.However,how gastrointestinal microbes respond to diet-induced MFD are still unclear.In order to investigate the changes in gastrointestinal bacterial populations during MFD and explore the mechanism of MFD,eight primiparous Holstein cows were randomly assigned to treatment sequences in a 2×2 change-over experiment.Each period was 23 d,including the 16d induction phase and the 7d recovery phase.During the induction phase,the cows of Control group were fed a low-starch and low-oil diet（the ratio of concrete to roughage is 50:50）,and the cows of the Treatment group was fed a high-starch and high-oil diet（266 g/kg of ground corn and 46 g/kg of soybean oil were added in the Control diet,DM basis）;all the cows were fed the Control diet during the subsequent recovery phase.During the sampling period,milk,rumen fluid and feces samples were collected,and the changes of productivity,rumen and hindgut fermentation,bacterial flora in dairy cows were detected,which provided a theoretical basis for further exploring the mechanism of MFD.The results show that:（1）When feeding a high-starch and high-oil diet,the milk fat percentage were significantly reduced to 2.87%,which indicated that the dairy cows were successfully induced to MFD.Meanwhile,DMI,milk yield,the 3.5%fat-corrected milk yield（FCM）,energy-corrected milk（EMC）,feed efficiency,milk fat yield,milk protein yield,lactose yield and SNF（solid-not-fat）yield of the Treatment group were significantly lower compared to the Control group.（2）When feeding a high-starch and high-oil diet,the NH₃-N concentration and molar ratio of acetate in the rumen of the Treatment group were significantly lower compared to the Control group.While the ruminal p H,volatile fatty acid concentration such as acetate,propionate and butyrate had no remarkable difference between two groups.（3）According to the rumen fluid bacterial flora sequencing result,Bacteroidetes,Firmicutes and Proteobacteria were predominant phylums.When feeding a high-starch and high-oil diet,the bacterial flora in rumen were significantly different between the two groups and the richness and diversity of the rumen bacterial flora in the Treatment group were significantly decreased.At the phyla levels,the relative abundance of Fibrobacteres in the Treatment group was significantly lower compared to the Control group,and the relative abundance of Actinobacteria was higher significantly.At the genus level,the most members of Bacteroides in the Treatment group decreased significantly,and the relative abundance of the genus such as Lachnospiraceae,Butyrivibrio and Coriobacteriaceae,which were associated with altered biohydrogenation reactions,were significantly increased,while the relative abundance of Fibrobacter,which is related to fiber degradation,was significantly decreased.（4）When feeding a high-starch and high-oil diet,the p H and the molar ratio of acetate in the hindgut were higher in the Treatment group compared to the Control group,while the molar proportion of butyrate increased significantly.As known in the time point curve analysis,an effect of treatment by time was detected on the concentration of TVFA in the feces.（5）According to the feces bacterial flora sequencing result,Bacteroidetes,Firmicutes,Actinobacteria and Proteobacteria were predominant phylums.When feeding a high-starch and high-oil diet,the bacterial flora in feces were significantly different between the two groups and the richness and diversity of the fecal bacterial flora in the Treatment group were significantly decreased.At the phyla levels,the relative abundance of Actinobacteria and Verrucomicrobia in the Treatment group were significantly decreased,while the relative abundance of Proteobacteria was increased significantly.At the genus level,the relative abundance of Succinivibrio was increased significantly,while the relative abundance of Ruminococcaceae and Bifidobacterium,known as probiotic,were decreased significantly.In summary,feeding a high-starch high-oil diet can cause MFD in dairy cows.At the same time,the fermentation activity and bacterial flora of the rumen and hindgut of dairy cows are closely related to the diet-induced MFD.the current study found that some bacteria related to milk fat synthesis were discovered,which provides a theoretical basis for the subsequent study regarding the mechanism of diet-induced MFD.更多还原