FIBER

Fiber has received a great deal of research attention among animal scientists because of its importance to the ruminant. In the ruminant, it represents the plant cell wall which is utilized as an energy source by the rumen microflora, and is extensively degraded.

In the monogastric animal, fiber represents the insoluble matter of plant cell walls which is indigestible by animal enzymes, but can be partially degraded by gastrointestinal microflora.

Fiber is actually very complex. It is a combination of at least four major components which are distinctly different in chemical composition. These four major components are cellulose, hemicellulose, lignin, and pectin and gums.

Because of the complexity of defining and measuring fiber, any procedure for its measurement must strike a compromise between a complete, fractionated measurement of all of the various species, and a simplified system involving grouping in different compounds (cellulose, hemicellulose, lignin and pectin). To say that a ration has "X" amount of fiber makes no sense without some understanding of the ingredients used and/or a knowledge of the amounts of each of the major fiber components that are present. The analysis of crude fiber generally includes the lignin and a portion of the cellulose and hemicellulose. Acid detergent fiber is thought to measure cell walls and is an estimate of all the lignin and cellulose. Neutral detergent fiber is an estimate of lignin, cellulose and hemicellulose. None of the above analyses include the pectin and gums.

The constituents of fiber affect the gastrointestinal tract differently, ultimately affecting the nutrition of the animal. Some fibers have a high water-holding capacity, which affects the speed at which the diet passes through the intestinal tract (transit time). Other fiber constituents have extensive cation-exchange capacity, which can bind dietary minerals.

Current research indicates that various fibers may have these physiological effects:

1. A decrease in the absorption of minerals;
2. The binding of bile acids which are integral to cholesterol homeostasis and fat absorption;
3. A change in the potency of intestinal toxins and carcinogens;
4. The production of volatile fatty acids which are used for energy or for inhibiting pathogens;
5. Changes in transit time;
6. Alterations in gastrointestinal bacteria.

The changes produced by fiber in these and other body functions have been implicated in colon cancer, diverticular disease, diabetes, atherosclerosis, coronary heart disease and hemorrhoids.