Structures and characteristics of carbohydrates in diets fed to pigs: a review

Abstract

The current paper reviews the content and variation of fiber fractions in feed ingredients commonly used in swine diets. Carbohydrates serve as the main source of energy in diets fed to pigs. Carbohydrates may be classified according to their degree of polymerization: monosaccharides, disaccharides, oligosaccharides, and polysaccharides. Digestible carbohydrates include sugars, digestible starch, and glycogen that may be digested by enzymes secreted in the gastrointestinal tract of the pig. Non-digestible carbohydrates, also known as fiber, may be fermented by microbial populations along the gastrointestinal tract to synthesize short-chain fatty acids that may be absorbed and metabolized by the pig. These non-digestible carbohydrates include two disaccharides, oligosaccharides, resistant starch, and non-starch polysaccharides. The concentration and structure of non-digestible carbohydrates in diets fed to pigs depend on the type of feed ingredients that are included in the mixed diet. Cellulose, arabinoxylans, and mixed linked β-(1,3) (1,4)-d-glucans are the main cell wall polysaccharides in cereal grains, but vary in proportion and structure depending on the grain and tissue within the grain. Cell walls of oilseeds, oilseed meals, and pulse crops contain cellulose, pectic polysaccharides, lignin, and xyloglucans. Pulse crops and legumes also contain significant quantities of galacto-oligosaccharides including raffinose, stachyose, and verbascose. Overall, understanding the structure, characteristics and measurable chemical properties of fiber in feed ingredients may result in more accurate diet formulations, resulting in an improvement in the utilization of energy from less expensive high-fiber ingredients and a reduction in reliance on energy from more costly cereal grains.

Keywords: Carbohydrate composition; Carbohydrates; Chemical structure; Feed ingredients; Fiber; Pigs.

Fig. 1

Chemical structure of monosaccharides that are commonly associated with digestible carbohydrates and fiber. Adapted from Albersheim et al. [40]

Fig. 2

Chemical structure of di- and oligosaccharides. Adapted from Bach Knudsen et al. [1]

Fig. 3

Chemical structure of amylose, amylopectin, and cellulose. Adapted from Bach Knudsen et al. [1]

Fig. 4

Chemical structure of arabinoxylans linked via a diferulic acid linkage. Adapted from Izydorczyk and Dexter [53] and Bach Knudsen [42]

Fig. 5

Chemical structure of mixed linked β-glucan and xyloglucan. Adapted from Bach Knudsen et al. [1]

Fig. 6

Chemical structure of homogalacturonan and rhamnogalacturonan-I. Adapted from Albersheim et al. [40]

Fig. 7

Chemical structure of rhamnogalacturonan-II. Adapted from Albersheim et al. [40]

Fig. 8

Chemical structure of xylogalacturonan and arabinogalactan-I

Fig. 9

Chemical structure of arabinogalactan-II