Nutrient digestibility of forage and nonforage rations in the ruminant

Pooled data from forage and nonforage digestibility trials with steers were analyzed. Forages were higher in total fiber content, principally cellulose; nonforages were lower in total fiber content, principally hemicellulose. The fiber fractions of forages and non-forages both together and separately were regressed upon their respective digestible fractions (P < .01). The results indicated significant linear relationships and coefficients of variation for the digestible fraction estimated from the total ranged from 4 to 20 percent. Regression of digestible upon total holocellulose (P < .01) indicated a greater association than either of the regressions of cellulose or hemicellulose. Cellulose content and lignification contributed 85 percent (P < .01) and 12 percent (P < .01) to digestible cellulose, respectively. Hemicellulose content and lignification explained 74 percent (P < .01) and 0.6 percent, respectively, of the variation in digestible hemicellulose. Neutral detergent soluble digestibility is highly dependent on ration cellulose and hemicellulose content, due possibly to rates of passage and digestion of the fibrous fractions. Differences in digestibility between forages and nonforages were attributed to differences in the total fiber fractions, indicating there was a continuum between concentrates and forage, when all rations were considered.