来源：Pig Progress
Much is being said about fibres in swine diets these days, but let us take a step back. What exactly are dietary fibres, why do diets have different levels of fibre content and how to step up fibre utilisation?
关于猪日粮中纤维的说法很多，但我们各退一步。膳食纤维是什么，为什么饲料中含有不同水平的纤维含量以及如何提高纤维利用率？
Much controversy exists regarding the physiological effects of fibre on swine production because the term ‘fibre’ is not always clearly defined. Chemically, crude fibre analysis accounts for small amounts of hemicellulose, some amounts of cellulose, and most of the lignin present in the cell wall of plant materials. Crude fibre, however, is of limited value to swine nutritionists because it does not offer meaningful information regarding its potential physiological benefits to the animal. Other methodologies to analyse the fibrous components in feedstuffs and feeds include:
· Neutral detergent fibre (NDF);
· Acid detergent fibre (ADF); and
· Total dietary fibre (TDF)
由于“纤维”的定义有时不是非常明确，纤维对生猪生产的影响存在很多争议。化学意义上，粗纤维分析包括少量半纤维素，一些纤维素和大多数存在于植物材料细胞壁中的木质素。然而，粗纤维对猪营养学家的价值有限，因为无法提供关于其对生猪的潜在生理益处的有意义信息。分析饲料和饲料中纤维成分的其他方法包括：
•中性洗涤纤维（NDF）;
•酸性洗涤纤维（ADF）;
•总膳食纤维（TDF）
Coloured scanning electron micrograph (SEM) of cellulose fibres at a magnification of 35 times. Photo: Dennis Kunkel | ANP | Science Photo Library
35倍数彩色扫描电子显微镜下的纤维素
While NDF offers some value to nutritionists by providing information regarding the insoluble fibre fraction in feed, it is generally accepted that TDF provides more nutritional-relevant information. The reason for this is because TDF determines soluble and insoluble fibre fractions. Soluble fibre is fermentable to a certain extent in the gastro-intestinal tract and hence confers some energy to pigs. Within the soluble fibre fraction of TDF included are non-starch polysaccharides (NSP), non-digestible oligosaccharides and resistant starch (RS), all of which serve as substrates for microbial fermentation in the gut.
虽然中性洗涤纤维通过饲料中不溶性纤维成分的信息为营养学家提供了一些价值，但人们普遍认为总膳食纤维可以提供更多与营养相关的信息。其原因是总膳食纤维可测定可溶性和不溶性纤维部分。可溶性纤维在胃肠道中可在一定程度上发酵，因此赋予猪一些能量。 总膳食纤维的可溶性纤维中包括非淀粉多糖（NSP）、非消化性低聚糖和抗性淀粉（RS），它们都可作为肠道中微生物发酵的底物。
Pigs and TDF
生猪与总膳食纤维
Pigs do not have the ability to digest TDF in the small intestine. Consequently, the TDF fraction of feedstuffs is only partially fermented in the small intestine and mostly in the large intestine. As a result of TDF fermentation, short-chain fatty acids are produced and absorbed thereby providing some energy to pigs. The majority of TDF fermentation takes place in the large intestine.
猪不具备在小肠中消化膳食纤维的能力。因此，饲料中的膳食纤维只有小部分在小肠中发酵并且主要在大肠中发酵。由于膳食纤维发酵而产生和吸收的短链脂肪酸，为猪提供了一些能量。大部分膳食纤维发酵发生在大肠中。
Physiologically, TDF exerts negative and positive effects in animals. The physicochemical characteristics of TDF may affect the water binding capacity, bulk density, swelling, and viscosity, and these may confer negative effects to pigs. For example, high levels of NSP may increase digesta viscosity which is associated with reduced digestion and absorption of nutrients. The reason for this, is because higher viscosity prevents the interaction between endogenous enzymes and nutrients, thus acting as a physical barrier which precludes efficient digestion.
在生理意义上，膳食纤维对生猪既有积极影响也有消极影响。膳食纤维的物理化学特性可能会影响水的结合能力、堆积密度、膨胀和粘度，这些可能会对猪产生负面影响。例如，非淀粉多糖含量高可能增加消化物粘度，从而削弱了营养物质的消化和吸收。其原因在于，较高的粘度会阻止内源性酶与营养素之间的相互作用，从而形成一道物理屏障，影响了有效消化。
Diets with high TDF may also lead to an increase in endogenous losses of nitrogen because epithelial cells in the gut are stimulated to proliferate due to high viscosity of diets. Bulk density also plays a role in the energy utilisation of pigs because it affects feed intake and the ability of pigs to consume sufficient energy to maintain growth.
饲料的高粘度会刺激肠道中的上皮细胞增殖，因此具有膳食纤维总量高的饲料也可导致内源性氮损失增加。体积密度也影响猪的能量利用，因为它影响采食量和猪消耗足够的能量以维持生长的能力。
Additionally, bulk density affects the weight of the gastro- intestinal tract of pigs, thereby affecting the amount of energy necessary for maintenance. Besides the potential problems regarding high TDF in diets, recent research has shed light into its potential benefits for animals. Many studies have demonstrated that fermentation of TDF in the large intestine promotes the growth of beneficial bacteria such as Lactobacillus species. These observations were generally associated with reduction in the incidence and severity of post-weaning diarrhoea.
另外，堆积密度也影响猪的胃肠道重量，从而影响维持所需的能量。除了高膳食纤维总量可能带来的潜在问题外，最近的研究还揭示了其对生猪的潜在益处。许多研究表明膳食纤维在大肠中的发酵促进了有益细菌，如乳杆菌属的生长。这些观察结果通常与断奶后腹泻的发生率和严重程度降低相关。
It has been shown that pigs fed diets containing barley or oats have an increased population of Lactobacillus species and Bifidobacterium species. These shifts in microbial population are likely associated with the β-glucans present in barley and oats, which have been shown to support the growth of beneficial bacteria at the expense of harmful bacteria. The positive effects of fibre on promoting gut health, however, may be associated with the type of fibre substrate available for fermentation as some studies have also reported a negative impact on gut health.
已经表明，在饲料中添加大麦或燕麦，猪体内乳杆菌属物种和双歧杆菌属物种的数量会增加。微生物种群的这些变化可能与大麦和燕麦中的β-葡聚糖有关，已经证明这些β-葡聚糖需要消灭有害细菌来支持有益菌的生长。然而，纤维对肠道健康的促进作用可能与可用于发酵的纤维底物的类型有关，因为一些研究还报道了对肠道健康的负面影响。
The amounts of fibre in feedstuffs vary considerably within and between plant species. Moreover, the type of fibre may also vary, thus affecting how fibre can be utilised by the animal.
饲料中的纤维量在植物物种内和植物物种之间变化很大。而且，纤维的类型也很多样，这也影响了生猪对纤维的利用。
There is also some variation on the fibre concentration in by-products from the biofuel industry because the amount of fibre present in such feedstuffs depends, in part, on the processing condition of raw materials and the ability to convert starch into fuel, among other reasons.
生物燃料工业的副产品中的纤维浓度也存在一些变化，因为这些饲料中存在的纤维量部分取决于原料的加工条件和将淀粉转化为燃料的能力等原因。
Improving the use of fibre in feedstuffs
改善饲料中纤维的使用
Multiple approaches have been used by the feed industry to improve utilisation of fibre in feedstuffs. Use of exogenous carbohydrases are likely the most used in practice but successful implementation of this practice is highly dependent on the ability to characterise and understand the fibrous composition of different feedstuffs and diets and the inherent properties of enzymes. Among carbohydrases, xylanases are likely the most utilised exogenous enzyme, because arabinoxylans (which are degraded by xylanase) make up the majority of the NSP present in cereal grains.
饲料行业已采用多种方法来提高饲料中纤维的利用率。外源性糖酶的使用可能是实践中最常用的，但是这种实践的成功实施高度取决于纤维特性和对不同饲料的纤维组成以及酶的固有性质的理解。在碳水化合物酶中，木聚糖酶可能是最常用的外源酶，因为阿拉伯木聚糖（由木聚糖酶降解而来）构成谷物中大部分的非淀粉多糖。
Carbohydrases have the ability to degrade the soluble fibre in feedstuffs and consequently reduce gut viscosity, thereby improving the absorption of nutrients. Other technologies such as mechanical, thermal, and chemical processes have been employed to improve the utilisation of fibre in feedstuffs. For example, the solubility and digestibility of NSP may be improved when roller milling is used compared with hammer milling. Extrusion has also been shown to increase the digestibility of energy in distillers dried grains with solubles (DDGS), which may reflect an improvement in fibre utilisation.
碳水化合物具有降解饲料中可溶性纤维的能力，从而降低肠粘度，进而改善营养素的吸收。其他技术如机械、加热和化学方法等已被用于提高饲料中纤维的利用率。例如，与锤磨相比，当使用辊磨时，非淀粉多糖的溶解度和消化率可以得到改善。挤压也被证明可以提高含有可溶物（DDGS）的干酒糟中能量的消化率，这可能反映出纤维利用率得到了提高。
Fibre-rich feedstuffs are becoming more prevalent in diets for pigs. The ability to precisely characterise and quantify the different fibre fractions within feedstuffs is paramount for successful utilisation of such feedstuffs. The interactions between fibrous components, gut microbiota, and the use of exogenous carbohydrases, and how they affect not only nutrient and energy utilisation but also gut health should be the focus of future research.
富含纤维的饲料在猪日粮中越来越普遍。精确特性和量化饲料中不同纤维成分的能力对于成功利用这些饲料是至关重要的。纤维成分、肠道微生物群和外源性糖酶的使用之间的相互作用，以及它们如何影响营养和能量利用及肠道健康，应该成为未来研究的重点。
（文/爱猪网记者刘坤颖编译，爱猪网原创请勿转载）
