Non-starch polysaccharides in the diets of young weaned piglets
Pluske, J.R., Kim, J.C., McDonald, D.E., Pethick, D.W. and Hampson, D.J. (2001) Non-starch polysaccharides in the diets of young weaned piglets. In: Varley, M.A. and Wiseman, J., (eds.) The weaner pig : nutrition and management. CABI Publishing, Wallingford, UK, pp. 81-112.
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Carbohydrates comprise between 60% and 80% of the digestible dry matter (DM) in the majority of feedstuff for weaner pigs. The carbohydrate ingested by piglets can be divided into one fraction (starch) that is targeted by the endogenous enzymes of the gastrointestinal tract (a-amylase), and another component (‘dietary fibre’, DF) that is digested predominantly in the terminal ileum and large intestine. The major constituent of DF in diets for young pigs influencing production, gut function and possibly enteric disease susceptibility is derived from non-starch polysaccharides (NSPs). Traditionally the ‘indigestible’ carbohydrate content of foodstuffs has been expressed as ‘crude fibre’, a term that provides no information regarding possible physico-chemical effects of NSP in vivo in the animal or its likely digestibility; simply because it is the residue remaining from extractions of the major plant cell wall components.
Non-starch polysaccharides are a large variety of polysaccharide molecules, often in association with phcnolic lignified polymers, protein and starch, that have glucosidic bonds other than the α-(1→4), (1→6) bonds of starch. The building blocks of plant cell wall polysaccharides are the pentoses (arabinose and xylose), hexoses (glucose, galactose and mannose), 6-deoxyhexoses (rhamnose and fucose) and uronic acids (glucuronic and galacturonic acids). These monomers are chemically linked to each other to build various NSPs in the plant cell walls of both cereals and legumes. The major NSPs of plant cell wails, therefore, comprise cellulose (linear β-glucan chains), non-cellulosic polysaccharides (arabinoxylans, mixed-linked β-glucans, mannans, galactans, xyloglucan) and pectic polysaccharides (polygalacturonic acids, which may be substituted with arabinan, galactan and arabinogalactan) (Theander et al, 1989; Lewis, 1993; Bach Knudsen, 1997; Choct, 1997). The NSPs, in turn, can be divided into the ‘soluble’ fraction and the ‘insoluble’ fraction. The term ‘soluble’ refers to solubility in water or weak alkali solutions. It is generally accepted that the large majority of NSPs exhibiting anti-nutritive properties in monogastric animals, or at least the broiler chicken, are water-soluble and give rise to viscous aqueous solutions even when present at relatively low levels (Annison, 1993).
The major polysaccharides present in grains and legumes are presented (as average values) in Table 5.1. However, and from a physiological perspective, it is important to consider also the variation that exists within a particular cereal, because this may deter mine some of the physicochemical properties of the grain in vivo that, in turn, are likely to have an effect on digestibility and performance. Further discussion of the implications of this variation will be discussed later in this chapter.
|Publication Type:||Book Chapter|
|Murdoch Affiliation:||School of Veterinary and Biomedical Sciences|
|Copyright:||© CAB International 2001|
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