瘤胃甲烷生成之體內外評估與整合應用

Abstract

反芻動物消化代謝過程中產生的甲烷無法被自身利用而需排出，造成2-18%的總能攝取量由此途徑損耗。若能減少反芻動物甲烷排放量，可減緩溫室效應又可提升動物生產效率。目前用於偵測甲烷排放的標準方法為呼吸室法，其成本高昂且單次可測試之實驗動物數很少，應用穩定且高效率的體外發酵系統可以同時間評估大量的飼糧組合在降低甲烷產生的潛力，但體外測試結果常有高估甲烷降低效果的問題。本研究將根據體外試驗建立甲烷生成的間接指標，以快速篩選出有效降低甲烷生成的飼糧調整組合，進一步搭配非侵入式的甲烷偵測設備，在餵飼現場建立可重複測定的簡易裝置，以期能逐步發展成有效率的解決方案。 本實驗第一部分以體外產氣試驗，評估杏鮑菇包青貯與胡蘿蔔青貯用於取代部份乳牛飼糧中之原料對甲烷產生之影響。結果顯示，在利用胡蘿蔔青貯儘管沒有顯著的降低甲烷生成，但可在不增加甲烷生成的同時，增加飼糧的體外消化率以提升其利用效率。利用菇包青貯取代之結果顯示，其體外消化率、產氣動力學、發酵速率與產氣量上並沒有顯著變化，降低了乙酸比例並提高丙酸比例，亦降低了甲烷生成。分析體外試驗樣品中，藉揮發性脂肪酸 (volatile fatty acid, VFA) 計算與輔酶coenzyme M (CoM) 之甲烷變化皆與氣相層析儀 (gas chromatography, GC) 分析之甲烷結果有相同趨勢，因此可做為評估飼糧處理組間相對甲烷生成的參考指標。透過體外試驗及間接指標，有助於分析甲烷降低的機制與飼糧代謝情形，並可有效率的篩選具降低甲烷潛力的飼糧。 體外試驗對甲烷評估之平台建立完成後，搭配自行開發之呼吸罩進行體內外雙向評估，實際測試比較乾乳牛與泌乳牛甲烷排放差異。結果顯示泌乳牛的甲烷生成較高，與其飼糧總發酵量與消化率高有關，其呼吸罩測定結果與體外試驗GC、VFA計算與CoM具有一樣的趨勢，顯示呼吸罩的可應用性。接著於商業牧場分別對初產 (F)、低產 (L)、中產 (M)與高產 (H) 四種不同泌乳牛餵飼TMR進行評估。結果顯示L組的中洗纖維消化率顯著較低，其原因與含較多低消化率的纖維有關。體外指標中，GC分析結果亦顯示了L組在單位可發酵基質有相對較高的甲烷產量，VFA推算值與GC結果有高度相關性(r=0.8764)，CoM濃度的結果亦與GC有高度相關性(r=0.7760)。體內呼吸罩試驗結果顯示，餵飼後2小時以單位乳量為基礎下，L組的甲烷生成量相對高，且四組甲烷生成的趨勢與體外試驗發酵GC、VFA推估值和CoM結果相符合。於台大牧場進行不同芻料/精料比例的餵飼結果顯示，隨著精料比例的提高，有助於提高消化率與丙酸生成，而體內呼吸罩試驗於餵飼後2小時計算單位可消化基質下甲烷產量，與體外GC計算單位可消化纖維甲烷產量、體內及體外VFA推估甲烷生成比例及CoM濃度具有相同趨勢，皆顯示精料比例越高甲烷產量越低。根據本實驗結果，自行開發之呼吸罩，可藉由換算單位泌乳量或是加入消化率計算單位可消化基質之甲烷產量，其結果亦與體外發酵24小時在相同樣品下的GC換算每單位可消化基質甲烷產量、VFA推估甲烷生成比例與CoM濃度結果均有相同趨勢。 綜觀本研究結果顯示，利用低成本建置穩定且高效率的體外評估平台，可減少直接進行動物餵飼試驗的動物需求數量及大幅降低先期篩選成本。利用GC、VFA以及CoM於體外發酵24與48小時的結果，結合自行開發之非侵入式的呼吸罩裝置於現場雙向驗證的結果，可強化未來實地驗證動物排放的能力，並快速建立國產原料在反芻動物餵飼價值資料，以應用於達成降低甲烷排放的適合原料搭配方式。

Methane (CH4) produced during ruminant digestion cannot be utilized by the animals, resulting in an energy loss of about 2-18% of total intake. Reducing CH4 emissions can mitigate greenhouse gas production and improve animal production efficiency. Diet manipulation is a moderate and sustainable strategy. The standard CH4 detection method, the respiration chamber, is costly and limited in animal numbers. Efficient in vitro fermentation systems can evaluate many diet combinations simultaneously but often overestimate CH4 reduction. This study aims to establish indirect CH4 production indicators from in vitro to quickly screen effective diet adjustments. Additionally, it will use non-invasive CH4 detection equipment to develop a simple, repeatable on-site measurement device, aiming to create an efficient solution. In the first experiment, an in vitro gas production platform was used to evaluate the impact of replacing ingredients with mushroom silage or carrot silage on methane production. Results showed that both mushroom silage and carrot silage significantly reduced the contents of neutral detergent fiber (NDF) and acid detergent fiber (ADF) (p<0.05). Although carrot silage did not significantly reduce CH4 production, it increased feed digestibility without increasing CH4 emissions, improving feed utilization efficiency. Replacing TMR with mushroom silage did not significantly change digestibility, fermentation rate, or gas production but reduced CH4 production and acetic acid (%). VFA calculated value and CoM concentration show the same trends as CH4 results from gas chromatography (GC) analysis, making them useful indicators for assessing relative CH4 production between different diets. Therefore, the in vitro gas production platform is useful for analyzing CH4 reduction mechanisms and feed metabolism, efficiently screening diets with CH4 reduction potential. After establishing the in vitro gas production platform, a non-invasive respiration mask will be used for dual in vitro and in vivo assessments at NPUST to compare CH4 emissions between dry and lactating cows. Results showed higher CH4 production in lactating cows, correlated with greater fermentation and digestibility. The mask results aligned with in vitro GC, VFA, and CoM trends, demonstrating its applicability. At a commercial farm, four TMR diets for first (F), low (L), medium (M), and high (H) yielding dairy cows were analyzed. The L group had lower NDF digestibility and higher CH4 productionm (mg/ g digestible DM), with high correlation between GC, VFA calculated results (r = 0.8764), and CoM concentrations (r = 0.7760). Mask in vivo measurements showed the L group had the highest CH4 production (mg/ kg milk production), consistent with in vitro results. At NTU farm, different forage/concentrate ratios (F:C) showed higher concentrates increased digestibility and propionate production. Mask in vivo measurements of CH4 per digestible substrate matched with CH4 production under per unit digestible NDF (mg/ g NDFD), in vivo and in vitro VFA calculated CH4 % and CoM trends, showing lower CH4 with higher concentrate ratios. Overall, mask results aligned with in vitro GC, VFA, and CoM measurements, confirming method consistency. This study demonstrates that a low-cost, efficient in vitro platform can reduce the number of animals needed for feeding trials and lower screening costs. Using 24- hour in vitro GC, VFA, and CoM results, combined with a non-invasive respiration mask for on-site verification, enhances real-world validation of animal emissions. This approach helps establish the feeding value of domestic ingredients and identifies optimal combinations to reduce CH4 emissions.