Clinic for Zoo Animals, Exotic Pets and Wildlife, Vetsuisse Faculty, University of Zurich, 8057 Zurich, Switzerland.
ETH Zurich, Institute of Agricultural Sciences, 8092 Zurich, Switzerland.
Animal. 2020 Mar;14(S1):s113-s123. doi: 10.1017/S1751731119003161.
Methane (CH4) production is a ubiquitous, apparently unavoidable side effect of fermentative fibre digestion by symbiotic microbiota in mammalian herbivores. Here, a data compilation is presented of in vivo CH4 measurements in individuals of 37 mammalian herbivore species fed forage-only diets, from the literature and from hitherto unpublished measurements. In contrast to previous claims, absolute CH4 emissions scaled linearly to DM intake, and CH4 yields (per DM or gross energy intake) did not vary significantly with body mass. CH4 physiology hence cannot be construed to represent an intrinsic ruminant or herbivore body size limitation. The dataset does not support traditional dichotomies of CH4 emission intensity between ruminants and nonruminants, or between foregut and hindgut fermenters. Several rodent hindgut fermenters and nonruminant foregut fermenters emit CH4 of a magnitude as high as ruminants of similar size, intake level, digesta retention or gut capacity. By contrast, equids, macropods (kangaroos) and rabbits produce few CH4 and have low CH4 : CO2 ratios for their size, intake level, digesta retention or gut capacity, ruling out these factors as explanation for interspecific variation. These findings lead to the conclusion that still unidentified host-specific factors other than digesta retention characteristics, or the presence of rumination or a foregut, influence CH4 production. Measurements of CH4 yield per digested fibre indicate that the amount of CH4 produced during fibre digestion varies not only across but also within species, possibly pointing towards variation in microbiota functionality. Recent findings on the genetic control of microbiome composition, including methanogens, raise the question about the benefits methanogens provide for many (but apparently not to the same extent for all) species, which possibly prevented the evolution of the hosting of low-methanogenic microbiota across mammals.
甲烷（CH4）的产生是哺乳动物共生微生物在发酵纤维消化过程中普遍存在的、显然不可避免的副产物。在这里，我们从文献和迄今为止未发表的测量结果中，汇集了 37 种仅以饲料为食的哺乳动物食草动物个体的体内 CH4 测量数据。与之前的说法相反，CH4 的绝对排放量与 DM 摄入量呈线性比例，CH4 产量（每 DM 或总能量摄入量）与体重没有显著差异。因此，CH4 生理学不能被认为代表了内在的反刍动物或食草动物的体型限制。该数据集不支持 CH4 排放强度在反刍动物和非反刍动物、前肠发酵者和后肠发酵者之间的传统二分法。一些啮齿动物后肠发酵者和非反刍动物前肠发酵者排放的 CH4 量与体型相似、摄入量水平、食糜滞留或肠道容量相似的反刍动物一样高。相比之下，马科动物、袋鼠和兔子产生的 CH4 很少，其大小、摄入量水平、食糜滞留或肠道容量的 CH4：CO2 比值很低，因此这些因素不能解释种间变异。这些发现得出的结论是，除了食糜滞留特性或反刍或前肠的存在之外，其他尚未确定的宿主特异性因素会影响 CH4 的产生。每消化纤维的 CH4 产量的测量表明，在纤维消化过程中产生的 CH4 量不仅在不同物种之间而且在同一物种内都有所不同，这可能指向微生物区系功能的变化。最近关于微生物组组成的遗传控制的发现，包括产甲烷菌，提出了一个问题，即产甲烷菌对许多（但显然不是对所有）物种提供了什么好处，这可能阻止了低产甲烷微生物在哺乳动物中的宿主进化。
