Department of Animal Sciences, Institute of Food and Agricultural Sciences, University of Florida, Gainesville 32611.
Department of Animal Sciences, Institute of Food and Agricultural Sciences, University of Florida, Gainesville 32611.
J Dairy Sci. 2019 Jun;102(6):5726-5755. doi: 10.3168/jds.2018-15334. Epub 2019 Mar 28.
The forage lignocellulosic complex is one of the greatest limitations to utilization of the nutrients and energy in fiber. Consequently, several technologies have been developed to increase forage fiber utilization by dairy cows. Physical or mechanical processing techniques reduce forage particle size and gut fill and thereby increase intake. Such techniques increase the surface area for microbial colonization and may increase fiber utilization. Genetic technologies such as brown midrib mutants (BMR) with less lignin have been among the most repeatable and practical strategies to increase fiber utilization. Newer BMR corn hybrids are better yielding than the early hybrids and recent brachytic dwarf BMR sorghum hybrids avoid lodging problems of early hybrids. Several alkalis have been effective at increasing fiber digestibility. Among these, ammoniation has the added benefit of increasing the nitrogen concentration of the forage. However, few of these have been widely adopted due to the cost and the caustic nature of the chemicals. Urea treatment is more benign but requires sufficient urease and moisture for efficacy. Ammonia-fiber expansion technology uses high temperature, moisture, and pressure to degrade lignocellulose to a greater extent than ammoniation alone, but it occurs in reactors and is therefore not currently usable on farms. Biological technologies for increasing fiber utilization such as application of exogenous fibrolytic enzymes, live yeasts, and yeast culture have had equivocal effects on forage fiber digestion in individual studies, but recent meta-analyses indicate that their overall effects are positive. Nonhydrolytic expansin-like proteins act in synergy with fibrolytic enzymes to increase fiber digestion beyond that achieved by the enzyme alone due to their ability to expand cellulose microfibrils allowing greater enzyme penetration of the cell wall matrix. White-rot fungi are perhaps the biological agents with the greatest potential for lignocellulose deconstruction, but they require aerobic conditions and several strains degrade easily digestible carbohydrates. Less ruminant nutrition research has been conducted on brown rot fungi that deconstruct lignocellulose by generating highly destructive hydroxyl radicals via the Fenton reaction. More research is needed to increase the repeatability, efficacy, cost effectiveness, and on-farm applicability of technologies for increasing fiber utilization.
饲料木质纤维素复合物是限制奶牛利用纤维中营养物质和能量的最大因素之一。因此，已经开发了几种技术来提高奶牛对饲料纤维的利用率。物理或机械加工技术可减小饲料颗粒大小和肠道填充度，从而增加采食量。这些技术增加了微生物定植的表面积，并可能提高纤维利用率。具有较低木质素的棕色中脉突变体（BMR）等遗传技术是提高纤维利用率最具可重复性和实用性的策略之一。新型 BMR 玉米杂交种比早期杂交种产量更高，而最近的短节间矮化 BMR 高粱杂交种避免了早期杂交种的倒伏问题。几种碱都能有效地提高纤维的消化率。其中，氨化除了增加饲料中的氮浓度外，还有额外的好处。然而，由于成本和化学品的腐蚀性，这些技术很少被广泛采用。尿素处理较为温和，但需要有足够的脲酶和水分才能发挥作用。氨纤维膨胀技术利用高温、高湿度和高压来降解木质纤维素，比单独氨化更彻底，但它发生在反应器中，因此目前在农场中不可用。增加纤维利用率的生物技术，如应用外源纤维分解酶、活酵母和酵母培养物，在个别研究中对饲料纤维消化的影响不确定，但最近的荟萃分析表明，它们的总体效果是积极的。非水解扩展蛋白样蛋白通过与纤维分解酶协同作用，扩大纤维素微纤丝的膨胀，使更多的酶穿透细胞壁基质，从而增加纤维消化，超过单独使用酶的效果。白腐真菌也许是木质纤维素解构最具潜力的生物制剂，但它们需要有氧条件，而且几种菌株容易降解易消化的碳水化合物。对通过芬顿反应产生高破坏性羟基自由基来解构木质纤维素的棕色腐烂真菌的反刍动物营养研究较少。需要更多的研究来提高提高纤维利用率的技术的可重复性、功效、成本效益和在农场的适用性。
