Romero J J, Ma Z X, Gonzalez C F, Adesogan A T
Department of Animal Sciences, Institute of Food and Agricultural Sciences, University of Florida, Gainesville 32608.
Department of Microbiology and Cell Science, Institute of Food and Agricultural Sciences, University of Florida, Gainesville 32608.
J Dairy Sci. 2015 Jul;98(7):4659-72. doi: 10.3168/jds.2014-8849. Epub 2015 Apr 29.
Our objectives were to examine if adding metal ion cofactors (COF) to exogenous fibrolytic enzymes (EFE) would increase the beneficial effects of the EFE on the preingestive hydrolysis and in vitro digestibility and fermentation of bermudagrass haylage. In experiment 1, 5 COF (Mn(2+), Co(2+), Fe(2+), Ca(2+), and Mg(2+)) were screened to select the best candidates for synergistically enhancing release of water-soluble carbohydrates (WSC) from bermudagrass haylage by 5 EFE. The 5 EFE (1A, 2A, 11C, 13D, and 15D) were sourced from Trichoderma reesei and Aspergillus oryzae and they were the most effective of 12 EFE at increasing the neutral detergent fiber digestibility of bermudagrass haylage in a previous trial. Adding 1mM of each of the COF to EFE 2A or 11C synergistically increased release of WSC from bermudagrass haylage, as did adding (1mM) Fe(2+) to 1A, Mn(2+), Co(2+), or Fe(2+) to 13D, or Co(2+)or Fe(2+) to 15D. The greatest release of WSC responses were obtained by adding Mn(2+) to 11C (38%) or by adding Fe(2+) to 2A or 13D (10 and 21.9%, respectively). In experiment 2, the effect of increasing the COF dose on in vitro digestibility and fermentation of bermudagrass haylage was examined using the best EFE-COF combinations from experiment 1. Effects of adding increasing doses of these COF on EFE-mediated changes in vitro digestibility depended on the COF-EFE combination. Adding 10mM Mn(2+) alone to bermudagrass haylage increased DMD and NDFD by 2.7 and 6.3% and adding 11C alone increased these measures by 6.6 and 15.5%, respectively. However, adding 10mM Mn(2+) with 11C resulted in 3.5 and 8.1% increases in DMD and NDFD, respectively, beyond the increases caused by adding 11C alone. Adding Fe(2+) to 2A had no effects on EFE-mediated digestibility responses, but 2A prevented adverse effects of adding Fe(2+) alone on DMD and NDFD. In contrast, adding Fe(2+) to 13D reduced the increases in DMD and NDFD caused by adding the EFE alone. This study shows that adding COF to EFE can synergistically increase, decrease, or not affect the hydrolytic effects of EFE on bermudagrass haylage cell walls. The outcome depends on the specific EFE-COF combination and the COF dose. More research is required to understand the mechanisms resulting in these outcomes to exploit beneficial effects of COF on EFE.
我们的目标是研究向外源纤维分解酶（EFE）中添加金属离子辅因子（COF）是否会增强EFE对百慕大青贮干草采食前水解以及体外消化率和发酵的有益作用。在实验1中，筛选了5种COF（Mn(2+)、Co(2+)、Fe(2+)、Ca(2+)和Mg(2+)），以选择能与5种EFE协同增强从百慕大青贮干草中释放水溶性碳水化合物（WSC）的最佳候选物。这5种EFE（1A、2A、11C、13D和15D）来源于里氏木霉和米曲霉，并且在之前的试验中，它们是12种EFE中提高百慕大青贮干草中性洗涤纤维消化率最有效的。向EFE 2A或11C中添加1mM的每种COF均可协同增加从百慕大青贮干草中释放的WSC，向1A中添加（1mM）Fe(2+)、向13D中添加Mn(2+)、Co(2+)或Fe(2+)，以及向15D中添加Co(2+)或Fe(2+)也有同样效果。通过向11C中添加Mn(2+)（38%），或向2A或13D中添加Fe(2+)（分别为10%和21.9%）可获得最大的WSC释放响应。在实验2中，使用实验1中最佳的EFE-COF组合研究了增加COF剂量对百慕大青贮干草体外消化率和发酵的影响。添加这些COF的递增剂量对EFE介导的体外消化率变化的影响取决于COF-EFE组合。单独向百慕大青贮干草中添加10mM Mn(2+)可使干物质消化率（DMD）和中性洗涤纤维消化率（NDFD）分别提高2.7%和6.3%，单独添加11C可使这些指标分别提高6.6%和15.5%。然而，将10mM Mn(2+)与11C一起添加时，DMD和NDFD分别比单独添加11C时增加了3.5%和8.1%。向2A中添加Fe(2+)对EFE介导的消化率响应没有影响，但2A可防止单独添加Fe(2+)对DMD和NDFD产生的不利影响。相反，向13D中添加Fe(2+)会降低单独添加EFE所引起的DMD和NDFD的增加。本研究表明，向EFE中添加COF可协同增加、减少或不影响EFE对百慕大青贮干草细胞壁的水解作用。结果取决于特定的EFE-COF组合和COF剂量。需要更多研究来了解导致这些结果的机制，以利用COF对EFE的有益作用。
