Application of white-rot fungal fermented rice straw in lactating goat diet

Abstract

稻稈為台灣主要農業副產物之一，全年產量150萬公噸，與常用牧草比較其高木質素低消化率之特性飼養價值並不高。為有效利用副產物減少進口依賴，因此本研究利用具有降解木質素能力之白腐真菌 (Pleurotus eryngii) 進行稻稈固態發酵，並評估發酵後稻稈作為泌乳羊飼糧之可行性。經條件測試，選定以含水率60%稻稈作為基質，接種5%麥粒菌酛於24℃下固態發酵21天，進行一般成分分析，並以體外氣體生成技術 (In vitro gas production, IVGPT) 及掃描式電子顯微鏡 (Scanning electron microscope, SEM) 評估發酵稻稈品質及其結構變化。結果顯示，稻稈經14天及21天發酵後，粗蛋白含量增加 (0.31%及0.55% DM)，中洗纖維及酸洗木質素含量降低，SEM亦觀察到結構明顯崩解與碎裂。體外真消化率 (In vitro true digestibility, IVTD) 評估中，經發酵14天之稻稈由60%提高至67%。此外，IVGPT試驗結果顯示，經發酵7天之稻稈氣體生成量增加86 mL/g DM (230 vs. 144 mL/g DM)。體外試驗顯示稻稈經杏鮑菇菌固態發酵7天及14天後，可提高反芻動物之營養分利用率。使用20頭泌乳羊進行兩期各28天之飼養試驗，分為五個處理組：對照組 (百慕達乾草，佔飼糧乾物質20%)、25%稻稈或發酵稻稈 (以稻稈或發酵稻稈取代25%百慕達草)、50%稻稈或發酵稻稈 (取代50%百慕達草)。結果顯示，乾物質採食量處理組間並無顯著差異，分別為2.23、2.18、2.16、1.94及1.90 kg/day。對照組與25%發酵稻稈之產乳量顯著較50%發酵稻稈之產乳量較高 (2.65 v.s. 2.63 vs. 2.25 kg/day) (P < 0.05)。4% 乳脂校正乳 (Fat-corrected milk, FCM) 以25%發酵稻稈組顯著較50%發酵稻稈組好 (P < 0.05)。乳品質分析中，添加稻稈處理組顯著增加乳脂率，添加發酵稻稈則顯著使乳脂率降低 (P < 0.05)。乳蛋白、乳糖、非脂固形物及總固形物率，處理間均無顯著差異 (P > 0.05)。各項乳成分產量中，50%發酵稻稈處理組均顯著較其他四組差 (P < 0.05)。泌乳羊飼糧中以發酵稻稈取代50%百慕達草對生產性能有明顯不利之影響，然發酵稻稈取代25%百慕達草之生產性能有提升產乳性能之趨勢，但對泌乳品質則無顯著之影響。綜上所述，白腐真菌發酵稻稈可提高此農副產物之營養價值，具替代性芻料之潛力。

Rice straw is one of the main agricultural byproducts in Taiwan. Annual yield of rice straw was about 1.5 million tons (COAG, 2011).Because of their high lignin and low protein contents, cause low digestibility and feeding values for ruminants. To improve the feed quality of rice straw, using solid-state fermentation (SSF) with white rot fungi which is known for capability of degrading lignin. The purpose of this project is to improve the utilization of fibrous byproduct rice straw as ruminant feed by using SSF with white rot fungi. Base on the optimal condition, water content 60% rice straw was inoculated with spawns of Pleurotus eryngii and incubated under 24℃ for 21 days. Rice straw samples were analyzed for Chemical composition, and In vitro gas production technique (IVGPT) and Scanning Electron Microscope (SEM) were used for evaluating the quality of fermented straw and the degradability of structural carbohydrates. The result showed that crude protein increased after 14 and 21 day fermentation (0.31 and 0.55%, respectively). The structure of fermented straw is apparent disintegrative and fragmental. According the results of in vitro tests, after 14 day fermentation, straw improved In vitro true nutrient digestibility (IVTND) from 60% to 67%. Also, fermented straw's total gas production was 230 mL/ g DM after 7 day fermentation whilst control's total gas production was 230 mL/ g DM. In vitro experiments showed that utilization of rice straw for rumen microbes can be improved after 14 and 21 day fermentation with white rot fungi. 20 lactating goats randomly were used for two terms 28-day feeding trial which is divided into five treatments: control group (Bermuda hay); 25% fermented or unfermented rice straw group (replacing 25% of Bermuda hay); 50% fermented or unfermented rice straw group (replacing 50% Bermuda hay in control group). Dry matter intake (DMI), milk yield, milk composition and weight changes were recorded. Results showed that there were no significant differences among the groups (2.23; 2.18; 2.16; 1.94; 1.90 kg/day, respectively). 25% fermented rice straw group had similar milk yield with control group and were significant higher than 50% fermented rice straw group (2.63; 2.65; 2.25 kg/day, respectively) (P < 0.05). 25% fermented rice straw group had significant higher fat calculated milk (FCM) than 50% fermented rice straw group (P < 0.05).In quality of milk, 50% fermented rice straw group had significant lower milk fat (P < 0.05), but no significant differences among the other milk quality. In conclusion, it was significant negative effect that feeding lactating goats with white rot fungi treated rice straw replacing 50% of Bermuda hay. However, diet replacing 25% of Bermuda hay with fermented rice straw had a positive effect in milk yield, but no significant differences with rice straw treatment in milk quality. White rot fungi treated rice straw does improve its feed quality and can be used as a potential alternative feedstuff for traditional forage.