Feeding 100% forage rape to sheep consistently lowers methane emissions per unit of intake (CH4/DMI) compared to those fed 100% ryegrass pasture. However, forage rape is usually supplemented with other feeds, which might impact the mitigation potential provided by forage rape. The objective of this study was to determine the effect of substituting ryegrass with graded levels of forage rape in the diet of lambs on methane emissions and rumen fermentation characteristics. Seventy wether lambs (n=14/treatment) were fed a ryegrass-based pasture substituted with 0, 25, 50, 75 and 100% of forage rape (Brassica napus; FR0, FR25, FR50, FR75, FR100, respectively) on a dry matter basis. Methane emissions and dry matter intake were measured for 48 h in respiration chambers and a rumen fluid sample was collected. CH4/DMI decreased (P < 0.01) with increasing forage rape inclusion in the diet, so that sheep fed FR100 and FR75 emitted 34 % and 11% less, respectively, than those fed FR0. CH4/DMI differences for lambs fed FR25 and FR50 were much smaller (< 6%) relative to FR0. The pH of rumen fluid decreased (P < 0.01) at higher levels of forage rape inclusion in the diet (FR75 and FR100) compared to low levels of inclusion (FR0, F25 and F50). The proportion of ruminal acetate was least in FR100 (30%) followed by FR75 (10%), FR50 (8%) and FR25 (4%) compared with FR0 (P < 0.001). The proportion of propionate plus succinate was greater for FR100 (+40%), FR75 (+28%) and FR50 (+29%) compared with FR0, with FR25 intermediate (P < 0.001). The methanol concentration, and ethanol and propanol proportions in rumen fluid were greater for FR100 compared with any other treatment (P < 0.001). In conclusion, CH4/DMI decreased at high levels of forage rape inclusion in the diet and especially feeding FR100 was associated with a pronounced shift in rumen fermentation profile, with significant presence of succinate, ethanol, propanol, methanol, valerate and caproate.

中文翻译：

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在羔羊的日粮中用不同水平的油菜代替黑麦草牧场可减少甲烷排放并增加瘤胃中的丙酸、琥珀酸和伯醇

与饲喂 100% 黑麦草牧场的羊相比，饲喂 100% 的草料油菜给绵羊持续降低了每单位摄入量的甲烷排放量 (CH4/DMI)。然而，草料油菜通常辅以其他饲料，这可能会影响草料油菜提供的缓解潜力。本研究的目的是确定在羔羊日粮中用不同水平的草料油菜替代黑麦草对甲烷排放和瘤胃发酵特性的影响。用 0、25、50、75 和 100% 的草料油菜（Brassica napus；分别为 FR0、FR25、FR50、FR75、FR100）代替黑麦草为 70 只羔羊（n = 14/处理）喂食干物质基础。在呼吸室中测量 48 小时的甲烷排放量和干物质摄入量，并收集瘤胃液样品。CH4/DMI 下降 (P < 0. 01) 随着日粮中草料油菜含量的增加，喂食 FR100 和 FR75 的绵羊排放量分别比喂食 FR0 的绵羊少 34% 和 11%。相对于 FR0，饲喂 FR25 和 FR50 的羔羊的 CH4/DMI 差异要小得多（＜6%）。与低水平添加（FR0、F25 和 F50）相比，日粮中添加高水平的草料油菜（FR75 和 FR100）瘤胃液的 pH 值降低（P < 0.01）。与FR0相比，FR100（30%）的瘤胃乙酸比例最低，其次是FR75（10%）、FR50（8%）和FR25（4%）（P＜0.001）。与 FR0 相比，FR100 (+40%)、FR75 (+28%) 和 FR50 (+29%) 的丙酸盐加琥珀酸盐的比例更大，其中 FR25 中间体 (P < 0.001)。甲醇浓度，与任何其他处理相比，FR100 瘤胃液中乙醇和丙醇的比例更高（P < 0.001）。总之，在日粮中添加高水平的草料油菜时，CH4/DMI 会降低，尤其是饲喂 FR100 与瘤胃发酵曲线的显着变化有关，其中显着存在琥珀酸、乙醇、丙醇、甲醇、戊酸和己酸。