This study aimed to characterize the rumen microbiota structure of cattle grazing in tropical rangelands throughout seasons and their responses in rumen ecology and productivity to a N-based supplement during the dry season. Twenty pregnant heifers grazing during the dry season of northern Australia were allocated to either N-supplemented or un-supplemented diets and monitored through the seasons. Rumen fluid, blood, and feces were analyzed before supplementation (mid-dry season), after two months supplementation (late-dry season), and post supplementation (wet season). Supplementation increased average daily weight gain (ADWG), rumen NH₃–N, branched fatty acids, butyrate and acetic:propionic ratio, and decreased plasma δ¹⁵N. The supplement promoted bacterial populations involved in hemicellulose and pectin degradation and ammonia assimilation: Bacteroidales BS11, Cyanobacteria, and Prevotella spp. During the dry season, fibrolytic populations were promoted: the bacteria Fibrobacter, Cyanobacteria and Kiritimatiellaeota groups; the fungi Cyllamyces; and the protozoa Ostracodinium. The wet season increased the abundances of rumen protozoa and fungi populations, with increases of bacterial families Lachnospiraceae, Ruminococcaceae, and Muribaculaceae; the protozoa Entodinium and Eudiplodinium; the fungi Pecoramyces; and the archaea Methanosphera. In conclusion, the rumen microbiota of cattle grazing in a tropical grassland is distinctive from published studies that mainly describe ruminants consuming better quality diets.

中文翻译：

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热带牧场牛瘤胃微生物结构和代谢物的季节性和营养补充反应


本研究旨在表征热带牧场放牧的牛在整个季节的瘤胃微生物群结构，以及它们在旱季对基于氮的补充物的瘤胃生态和生产力的反应。澳大利亚北部旱季期间放牧的 20 头怀孕小母牛被分配给补充氮或不补充氮的日粮，并在整个季节进行监测。在补充前（旱季中期）、补充两个月后（旱季末）和补充后（雨季）对瘤胃液、血液和粪便进行分析。补充剂增加了平均日增重 (ADWG)、瘤胃 NH ₃ –N、支链脂肪酸、丁酸和乙酸：丙酸比率，并降低血浆 δ ¹⁵ N。补充剂促进了参与半纤维素和果胶降解以及氨同化的细菌种群：拟杆菌目BS11 、蓝细菌和普氏菌属。在旱季，纤维溶解菌群得到促进：纤维杆菌属、蓝藻菌属和 Kiritimatiellaeota 菌群；真菌Cyllamyces ；和原生动物介形虫。雨季增加了瘤胃原生动物和真菌种群的丰度，其中Lachnospiraceae 、 Ruminococcaceae和Muribaculaceae细菌家族有所增加；原生动物Entodinium和Eudiplodinium ；真菌Pecoramyces ；和古细菌甲烷圈。 总之，在热带草原放牧的牛的瘤胃微生物群与已发表的主要描述反刍动物消耗更高质量饮食的研究不同。