Methane emissions from ruminants enhance global warming and lead to a loss of feed energy. The emissions are low when fed brassica crops, but the factors contributing to low emissions are unknown. A meta‐analysis was conducted with individual animal data collected from seven experiments. In these experiments, methane emissions were measured using respiration chambers. Animal characteristics, feed chemical composition and rumen fermentation parameters were included for the analysis using multiple regression models. Feed intake level, animal live weight and age were animal factors that were weakly and negatively related to methane yield (g/dry matter intake). The duration in which sheep were fed brassica crops was a significant contributor in the model, suggesting that the effect on emissions diminishes with time. Among a range of feed chemical composition characters, acid detergent fibre and hot‐water‐soluble carbohydrate contributed significantly to the model, suggesting that both structural and soluble carbohydrates affect methane formation in the rumen. There was no significant correlation between the concentration of sulphate in brassicas and emissions, but nitrate was moderately and negatively correlated with methane yield (r = −.53). Short‐chain fatty acid profiles in the rumen of animals fed brassicas were different from those fed pasture, but these parameters only moderately correlated to methane emissions (r = .42). Feeding forage rape resulted in low rumen pH. The pH before morning feeding was strongly correlated to methane yield (r = .90). Rumen pH, together with microbial communities mediated by pH, might lead to low emissions. Bacteria known to produce hydrogen were relatively less abundant in the rumen contents of brassica‐fed animals than pasture‐fed animals. In conclusion, animal and feed factors, rumen fermentation and microbial communities all affect methane emissions to some extent. The interactions of these factors with each other thus contribute to methane emissions from brassica‐fed sheep.

中文翻译：

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与饲喂芸苔属植物的绵羊的甲烷排放相关的动物、饲料和瘤胃发酵特性

反刍动物的甲烷排放会加剧全球变暖并导致饲料能量损失。饲喂芸苔属作物时排放量较低，但导致低排放量的因素尚不清楚。对从七个实验中收集的个体动物数据进行了荟萃分析。在这些实验中，使用呼吸室测量甲烷排放。动物特征、饲料化学成分和瘤胃发酵参数被纳入使用多元回归模型进行分析。采食量水平、动物活重和年龄是与甲烷产量（g/干物质摄入量）呈弱负相关的动物因素。绵羊喂食芸苔属作物的持续时间是模型中的一个重要因素，表明对排放的影响随着时间的推移而减弱。在一系列饲料化学成分特征中，酸性洗涤纤维和热水可溶性碳水化合物对模型有显着影响，表明结构性碳水化合物和可溶性碳水化合物都会影响瘤胃中甲烷的形成。芸苔中硫酸盐浓度与排放量之间没有显着相关性，但硝酸盐与甲烷产量呈中度负相关。r  = -.53）。饲喂芸苔属植物的动物瘤胃中的短链脂肪酸谱与饲喂牧草的动物不同，但这些参数与甲烷排放量仅适度相关 ( r  = .42)。饲喂草料油菜导致瘤胃 pH 值低。早晨饲喂前的 pH 值与甲烷产量（r = .90）。瘤胃 pH 值以及由 pH 值介导的微生物群落可能导致低排放。与牧草喂养的动物相比，芸苔属喂养动物的瘤胃内容物中已知能产生氢气的细菌相对较少。总之，动物和饲料因素、瘤胃发酵和微生物群落都会在一定程度上影响甲烷排放。因此，这些因素之间的相互作用会导致用芸苔属植物喂养的绵羊的甲烷排放。