The rate of digestion is slower for grasses because they remain in the rumen longer. Consequently, the total amount of digestion is greater for grasses. These differences between legumes and grasses can influence how rations are formulated for forage NDF and forage dry matter intake. The NSC fractions of forages can also influence digestion. Pectins are found in legumes but are negligible in grasses.
Pectins can ferment in the rumen as rapidly as starch, but they form acetate rather than propionate.
Most concentrates are too fine in particle size to provide a sufficient rumen mat, maintain normal rumen epithelial tissue, and stimulate sufficient chewing and eructation of gases. The NSC fractions of cereal grains usually contain over 80 percent starch. Most by-product feeds contain a larger portion of the NSC fractions as starch with the remainder as sugars and pectins. In concentrate ingredients, the availability and rate of digestion of the starch depend on the grain source and processing method. Extremes in either direction can adversely affect animal performance and health.