The Digestibility and Interrelationships of Various Carbohydrate Fractions of Pasture Herbage and a Resolution of the Components of Crude Fiber and Nitrogen-Free Extract

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Abstract
The composition and digestibility of timothy-mixed grasses were studied at 3 timothy growth stages. Steers were hand-fed herbage freshly clipped from areas adjacent to those grazed at the same time by other steers. At successive stages of maturity, the amts. of lignin, cellulose, and hemicelluloses increased progressively, whereas those of pectins, sugars, crude protein and ether extract decreased. Lignin was completely undigested and sugars were almost completely digested at all growth stages. The digestibility of all other constituents measured decreased progressively with advancing plant maturity. High negative correlations were obtained between the amts. of digestible dry matter and those of lignin, crude fiber and nitrogen-free extract in the grass. High negative correlations also were observed between the fecal contents of crude fiber, nitrogen-free extract, cellulose and hemicelluloses and the digestible dry matter content of the herbage, while a high positive correlation was observed between the crude protein content of feces and the digestible dry matter content of the herbage. Only small amts. of the dry matter of forages and feces were unresolved by analyses for lignin, hemicelluloses, cellulose, pectins, starch, sugars, crude protein, ether extract and ash. Although these constituents represent more or less distinct chemical groups this detailed analysis is expensive. It would appear that, in studies of the digestibility and composition of forage feeds, the replacement of the crude fiber analysis with an analysis for lignin and the measurement of the total carbo-hydrates by difference would result in the partitioning of nutrient groups having more meaning biologically than the presently employed proximate analysis.