Filling Dietary Space Vacated by Forages
Non-forage fiber sources
The primary advantage of NFFS is that they generally have higher energy concentrations and are much less filling than forages; feed intake is limited to a greater extent when the neutral detergent fiber (NDF) concentration of diet increases from forage compared with NFFS. They are commonly used as forage alternatives and vary widely in cost, availability, and chemical composition across type and location, and over time. Compared with cereal grains, NFFS are less likely to result in ruminal acidosis because they generally ferment more slowly, are not fermented to lactic acid, and because their rate of fermentation slows as ruminal pH declines. Like forages, NFFS often result in decreased propionate and increased acetate production in the rumen when substituted for cereal grains. A slower rate of fermentation and decreased propionate production might allow increased meal size and greater feed intake when meal size and feed intake are limited by absorbed propionate. However, substitution of NFFS for forage usually decreases the ration of acetate to propionate concentrations in the rumen and also decreases ruminal pH. Wisconsin researchers reported that NFFS were only about one half as effective as alfalfa at elevating milk fat concentration and were less effective at stimulating chewing activity when substituted for grain in low forage diets. Another Wisconsin experiment found that NFFS were only 27% as effective as alfalfa silage at increasing milk fat concentration. Therefore, when replacing forage with NFFS, the effects of NFFS, cereal grains, and other non-forage diet components on ruminal fermentation characteristics must be considered in selecting the type and amount of NFFS and the proportions of forage and grains that will be replaced.
The fiber concentrations (NDF and soluble fiber) of most NFFS are in the range observed for most forages (40 to 60% on a dry matter basis), but some NFFS have NDF concentrations exceeding 75% (oat hulls, cotton seed hulls, ground corn cobs). The primary difference in the fiber of NFFS compared with forages is that particle size of NFFS is smaller, so NFFS cannot provide long fibrous particles to form a rumen mat. While some NFFS such as cotton seed hulls and oat hulls are poor sources of energy and protein function only to dilute rapidly fermentable grains, most NFFS are also good sources of fermentable fiber. Some have additional value because they provide fatty acids and (or) ruminally undegraded protein. Soyhulls and beet pulp are excellent sources of fermentable fiber but have low protein and fatty acid concentrations. Crude protein concentrations of distiller’s grains, brewer’s grains, corn gluten feed, and whole linted cottonseeds are higher than most forages, ranging from 24 to 30% of DM. Whole cottonseeds, and to a lesser extent distiller’s grains, provide additional energy as fatty acids. The extent to which each NFFS should be used as a forage alternative depends upon its availability and price relative to other energy and protein sources, as well as its ability to substitute functionality for forage.