Methane production of two roughage and total mixed ration as influenced by cellulase and xylanase enzyme addition

In recent decades supplementation of animal feeds with exogenous fibrolytic enzymes has substantially improved digestibility and animal performance. However, information related to associated methane production is limited and inconsistent. This study evaluated the effect of cellulase and xylanase enzymes on in vitro methane production of Eragrostis curvula hay, maize (Zea mays) stover and a total mixed ration (TMR) at seven levels of the two enzymes. Feed samples were incubated for 2, 12, 24 and 48 h in an in vitro batch culture with buffer and rumen fluid, and fibrolytic enzymes. Gas production was measured using a pressure transducer connected to a data tracker, while methane gas was analysed using a gas chromatograph which was calibrated with standard CH4 and CO2. Increases in the level of enzyme application resulted in increases in gas volume, total volatile fatty acid (VFA) production, dry matter (DM) disappearance and associated increases in methane production. The linear increase in percentage and volume of methane production in tandem with increases in level of enzyme application might be due to increased fermentation, and organic matter degradability that resulted in a shift in VFA production towards acetate. Considering the efficiency of DM and neutral detergent fiber degradation and production of associated VFA with levels of enzymes, the use of 1 mg g−1 DM of enzyme can be a good option for the feeds tested. However, they cannot decrease methane production. It will be very important to consider other hydrogen sinks that can capture directly extra H+ produced by the addition of enzyme so that their supplementation could be very efficient and environmentally sound.

近数十年来，在动物饲料中添加外源性纤维分解酶（exogenous fibrolytic enzymes）已显著提升饲料消化率与动物生产性能。然而，有关其伴随甲烷生成的相关研究信息仍较为有限且结论不一致。本研究针对纤维素酶（cellulase）与木聚糖酶（xylanase）两种酶，在7个添加水平下，评估其对弯穗画眉草（Eragrostis curvula）干草、玉米（Zea mays）秸秆以及全混合日粮（TMR）的体外甲烷生成量的影响。试验将饲料样本与缓冲液、瘤胃液（rumen fluid）及纤维分解酶共同置于体外批量培养体系中，分别培养2、12、24与48小时。采用连接数据追踪器的压力传感器（pressure transducer）记录产气量，使用经标准甲烷（CH₄）与二氧化碳（CO₂）校准的气相色谱仪（gas chromatograph）分析甲烷含量。研究发现，酶添加水平提升可使产气量、总挥发性脂肪酸（VFA）生成量、干物质（DM）消失率以及甲烷生成量均显著升高。甲烷生成百分比与体积随酶添加水平提升呈线性增长，这可能源于发酵过程增强与有机物降解率提升，进而推动挥发性脂肪酸生成模式转向乙酸合成。综合干物质与中性洗涤纤维（neutral detergent fiber）的降解效率，以及不同酶添加水平下的挥发性脂肪酸生成情况，本次试验所测试的饲料采用1 mg·g⁻¹ DM的酶添加量为较佳选择，但该方案无法降低甲烷生成量。因此，探索可直接捕获酶添加所产生的额外H⁺的其他氢汇（hydrogen sinks）将极具研究价值，如此可使酶添加策略兼具高效性与环境友好性。