体外产气法研究不同NFC/NDF底物条件下外源纤维素酶的适宜添加水平

本试验旨在利用体外产气法研究不同非纤维性碳水化合物/中性洗涤纤维(non-fiber carbohydrates/neutral detergent fiber,NFC/NDF)的底物条件下外源纤维素酶(exogenous fibrolytic enzymes,EFE)对底物产气、降解和发酵特性的影响,找出不同底物条件下适宜的EFE添加水平。采用2×5交叉分组试验设计,5个NFC/NDF底物水平(0.85、1.02、1.19、1.36和1.53)分别添加5种水平的EFE(0,2,4,8和16mg/g DM)进行体外发酵。结果表明,1)不同NFC/NDF底物和EFE水平对体外总产气量(GP48)和产气参数(b、c和L)均有显著的影响(P0.05),且两因素互作显著(P0.05);底物1中,GP48、b和c值随EFE剂量的增加显著地线性和二次提高(P0.05),其中以16mg/g水平组较高,L值则呈相反趋势;底物2~4中,GP48、b和c值随EFE剂量增加显著地二次提高(P0.05),其中以4mg/g水平组较高。2)不同底物对干物质消失率(DMD)、酸性洗涤纤维降解率(ADFD)、中性洗涤纤维降解率(NDFD)和氮降解率(ND)均有显著的影响(P0.05),除ND外,EFE水平的添加效应呈现相似结果;底物1条件下,随着EFE添加剂量的提高,DMD、ADFD和NDFD显著地线性提高(P0.05),其中均以16 mg/g组最高(P0.05);而底物2~4中则以4mg/g组最高(P0.05)。3)不同NFC/NDF底物和EFE水平对瘤胃发酵参数均有显著影响(P0.05),除丙酸外,两种因素对其他指标的互作效应均显著(P0.05);在底物1~4条件下,随着EFE添加剂量的提高,除丙酸以外的其他发酵参数显著地线性和二次提高或降低(P0.05);底物1中,对照组pH值、氨态氮含量和丁酸摩尔浓度显著高于4、8和16mg/g组(P0.05),相反,16mg/g组的总挥发性脂肪酸(TVFA)、乙酸摩尔浓度和乙酸∶丙酸值较高;底物2~4条件下,pH值和氨态氮含量以4 mg/g组较低,而TVFA、乙酸摩尔浓度和乙酸∶丙酸值则呈相反的趋势。4)NFC/NDF=1.53时,添加EFE对体外产气参数、降解特性和发酵特性均无显著影响(P0.05)。由此,本试验发现,NFC/NDF底物影响了EFE的添加效应,NFC/NDF=0.85时,16mg/g EFE水平组有较好纤维降解效果;NFC/NDF分别为1.02、1.19和1.36时,EFE最适添加剂量为4mg/g;NFC/NDF=1.53时,底物中添加EFE没有正面效应。

Determination of appropriate levels of exogenous fibrolytic enzyme supplementation for substrates with different non-fiber carbohydrate/neutral detergent fiber ratios based on in vitro gas production

The objective of this study was to determine the appropriate level of exogenous fibrolytic enzyme (EFE) supplementation for substrates with different non-fiber carbohydrates/neutral detergent fiber (NFC/NDF) ratios.The experiment had a cross group design with two factors and five levels.Five substrates with different NFC/NDF ratios (0.85,1.02,1.19,1.36,and 1.53;sub1-5) were supplemented with EFE at five levels (0,2,4,8,and 16 mg/g dry matter/DM) and in vitro gas production,degradation,and fermentation profiles were determined.The results can be summarized as follows:1) The NFC/NDF ratio influenced total in vitro gas production (GP48) and gas production parameters (b,c,and L) (P＜0.05).The interaction between NFC/NDF ratio and EFE level was significant for gas production parameters (P＜0.05).In sub1,as the EFE level increased,GP48,b,and c increased (linear and quadratic effect,P＜0.05),and the highest GP48,b,and c were in the 16 mg/g EFE treatment;L showed the opposite trend.In the sub2-4 treatments,the highest GP48,b,and c were in the 4 mg/g EFE treatment.2) The NFC/NDF ratio in the substrate significantly affected the dry matter disappearance rate (DMD),acid detergent fiber degradation rate (ADFD),neutral detergent fiber degradation rate (NDFD),and nitrogen degradation rate (ND) (P＜0.05).The additive effects of EFE produced similar results,except for ND.In sub1,as the EFE dose increased,DMD,ADFD,and NDFD linearly increased (P＜0.05).The maximum values of DMD,ADFD,and NDFD were in the 16 mg/g EFE treatment in sub1 and in the 4 mg/g EFE treatment in sub2-4 (P＜0.05).3) The fermentation profile differed significantly among substrates with different NFC/NDF ratios and different levels of EFE supplementation (P＜0.05),and the two factors had a significant interaction effect (P＜0.05) for all fermentation parameters,except for propionate.For sub1-4,as the EFE levels increased,the fermentation profiles of all parameters except for propionate increased or decreased (quadratic effect,P＜0.05).In sub1,pH,ammonia-N,and the butyrate molar concentration were higher in the control group than in the 4,8 and 16 mg/g EFE treatments,but the acetate molar concentration and acetate:propionate ratio were higher in the 16 mg/g EFE treatment.The sub2-4 treatments showed lower pH and ammonia-N,and higher total volatile fatty acid (TVFA),acetate molar concentration,and acetate:propionate ratio.4) In the substrate with NFC/NDF=1.53,EFE supplementation had no effect on in vitro gas production,fiber degradation,or fermentation characteristics (P＞0.05).The results of this study showed that the NFC/NDF ratio influenced the response to EFE supplementation;NFC/NDF=0.85,16 mg/g EFE showed the best fiber degradation,and the optimum EFE dose was 4 mg/g for substrates with NFC/NDF ratios of 1.02,1.19,and 1.36.There was no positive effect of EFE on the substrate with NFC/NDF---1.53.