Abstract This study investigated the impacts of dietary laccase addition on performance, nutrient digestion, rumen fermentation and microbiota in bulls. Eight Holstein bulls with rumen cannula were allocated in a repeated 4 × 4 Latin square experiment design into four groups: control, low-laccase (LL), medium-laccase (ML) and high-laccase (HL) with 0, 0.2, 0.4 and 0.6 g/kg dietary dry matter (DM) of laccase addition, respectively. Addition of laccase did not influence DM intake but higher average daily gain and lower feed conversion ratio were found for bulls in ML group. Apparent nutrients digestibility elevated linearly with increasing laccase supplementation. Digestibility of DM and organic matter in ML, crude protein (CP) in ML and HL as well as neutral detergent fibre (NDF) and acid detergent fibre in LL, ML and HL were higher. Increasing laccase addition quadratically decreased ruminal pH, quadratically increased total volatile fatty acids content and changed ruminal fermentation mode to more propionate formation. Ruminal ammonia-N concentration decreased linearly. Ruminal degradability of concentrate CP and corn silage DM were higher for bulls in ML, but degradability of corn silage NDF was higher for bulls in ML and HL groups. Activities of cellobiase, α-amylase and laccase were higher for bulls in ML group. Populations of total bacteria, methanogens, Fibrobacter succinogenes, Ruminococcus albus, Butyrivibrio fibrisolvens, Prevotella ruminicola and Ruminobacter amylophilus increased linearly, but fungi and R. flavefaciens increased quadratically. Urine excretion of total purine derivatives was higher for bulls receiving medium or high level of laccase supplementation. The results suggested that dietary laccase supplementation increased performance and nutrient digestibility, and the appropriate addition level of laccase was 0.4 g/kg DM in bulls.

中文翻译：

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日粮添加漆酶对奶牛生长性能、营养消化、瘤胃发酵和微生物群的影响

摘要 本研究调查了日粮添加漆酶对公牛性能、营养消化、瘤胃发酵和微生物群的影响。在重复的 4 × 4 拉丁方实验设计中将八头带瘤胃插管的荷斯坦公牛分为四组：对照组、低漆酶 (LL)、中漆酶 (ML) 和高漆酶 (HL)，分别为 0、0.2、0.4和 0.6 g/kg 的漆酶添加量分别为膳食干物质 (DM)。添加漆酶不影响 DM 摄入量，但发现 ML 组公牛的平均日增重较高，饲料转化率较低。表观营养素消化率随着漆酶补充量的增加而线性升高。ML中的DM和有机物、ML和HL中的粗蛋白(CP)以及LL、ML和HL中的中性洗涤纤维(NDF)和酸性洗涤纤维的消化率较高。增加漆酶添加量会二次降低瘤胃 pH 值，二次增加总挥发性脂肪酸含量，并将瘤胃发酵模式改变为更多的丙酸形成。瘤胃氨氮浓度呈线性下降。ML 组公牛的浓缩 CP 和玉米青贮 DM 的瘤胃降解率较高，但 ML 和 HL 组公牛的玉米青贮 NDF 降解率较高。ML组公牛纤维二糖酶、α-淀粉酶和漆酶活性较高。细菌总数、产甲烷菌、琥珀酸纤维杆菌、白色瘤胃球菌、溶纤维酪弧菌、瘤胃普氏菌和淀粉样瘤胃杆菌的数量呈线性增加，但真菌和黄曲霉呈二次增加。接受中等或高水平漆酶补充剂的公牛的总嘌呤衍生物的尿液排泄量较高。