McNabb W C, Waghorn G C, Peters J S, Barry T N
Ag Research Grasslands, Palmerston North, New Zealand.
Br J Nutr. 1996 Oct;76(4):535-49. doi: 10.1079/bjn19960061.
Three experiments were undertaken to determine the effect of condensed tannin (CT) in Lotus pedunculatus (45-55 g extractable CT/kg DM) on the digestion of the principal leaf protein, ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39; Rubisco; fraction 1 leaf protein). In two of the experiments Lotus pedunculatus was fed to sheep, with one group receiving a continuous intraruminal infusion (per fistulum) of PEG (molecular weight 3500) to bind and inactivate the CT (PEG group). The other group, which did not receive PEG, was termed the control sheep (CT acting). Expt 3 involved in vitro incubations of Lotus pedunculatus in buffered rumen fluid, with and without PEG added. In all experiments the results have been interpreted in terms of the effects of CT on Rubisco solubilization and degradation. Disappearance of N and Rubisco from Lotus pedunculatus suspended in polyester bags in the rumen was used as a measure of solubilization. Degradation was defined as the disappearance of Rubisco from in vitro incubations of Lotus pedunculatus in rumen fluid. In Expt 1, CT reduced the digestion of Rubisco in the rumen from 0.96 to 0.72 of intake (P < 0.01). Rubisco digestion in the small intestine was 0.27 of intake in control sheep and 0.04 of intake in PEG sheep. In Expt 2, PEG had no effect on the loss of Rubisco from Lotus pedunculatus contained in polyester bags which were incubated in the rumen, hence CT did not affect the solubilization of Rubisco. Observations in Expt 1 were confirmed by in vitro incubations in Expt 3, where PEG addition substantially increased the rate of degradation of plant protein to NH3. Addition of PEG decreased the period of time taken to degrade 50% of the Rubisco from about 13.8 h to about 3.0 h. It was concluded that the action of CT reduced the digestion of Rubisco in the rumen of sheep fed on fresh Lotus pedunculatus, and that this was primarily due to the ability of CT to slow its degradation by rumen micro-organisms, without affecting its solubilization. Both fresh-minced, and freeze-dried and ground lotus were used for in sacco and in vitro incubations; however, fresh-minced lotus was more suitable for the evaluation of protein solubilization and degradation in fresh forages.
开展了三项试验，以确定百脉根（可提取缩合单宁45 - 55克/千克干物质）中的缩合单宁（CT）对主要叶片蛋白核酮糖-1,5-二磷酸羧化酶（EC 4.1.1.39；Rubisco；叶片蛋白1组分）消化的影响。在其中两项试验中，给绵羊饲喂百脉根，一组通过瘤胃瘘管持续瘤胃内输注聚乙二醇（PEG，分子量3500）以结合并使CT失活（PEG组）。另一组未接受PEG，称为对照绵羊（CT起作用）。试验3涉及在缓冲瘤胃液中对百脉根进行体外培养，添加或不添加PEG。在所有试验中，结果均根据CT对Rubisco溶解和降解的影响进行解读。瘤胃中悬浮于聚酯袋内的百脉根中氮和Rubisco的消失用作溶解的指标。降解定义为瘤胃液中百脉根体外培养时Rubisco的消失。在试验1中，CT使瘤胃中Rubisco的消化率从摄入量的0.96降至0.72（P < 0.01）。对照绵羊小肠中Rubisco的消化率为摄入量的0.27，PEG处理绵羊为摄入量的0.04。在试验2中，PEG对瘤胃中聚酯袋内百脉根中Rubisco的损失无影响，因此CT不影响Rubisco的溶解。试验1的观察结果在试验3的体外培养中得到证实，添加PEG显著提高了植物蛋白降解为NH₃的速率。添加PEG使降解50%的Rubisco所需时间从约13.8小时降至约3.0小时。得出的结论是，CT的作用降低了以新鲜百脉根为食的绵羊瘤胃中Rubisco的消化，这主要是由于CT能够减缓瘤胃微生物对其的降解，而不影响其溶解。新鲜切碎的、冻干并研磨的百脉根均用于袋瘤胃试验和体外培养；然而，新鲜切碎的百脉根更适合用于评估新鲜牧草中蛋白质的溶解和降解。
