Utilization of Dietary Fiber from Alfalfa by Growing Swine. I. Apparent Digestibility of Diet Components in Specific Segments of the Gastrointestinal Tract1

Abstract

Yorkshire weanling barrows weighing an average of 17 kg were assigned in four groups of eight pigs in each of two replicates (64 pigs) to a completely randomized experiment in a 2 × 4 × 4 factorial arrangement (slaughtered at 48 or 89 kg; fed 0, 20, 40 or 60% alfalfa meal; slaughtered at 2, 4, 8 or 12 hr after the last feeding). A level of 20% alfalfa meal, resulting in a level of 26% cell wall in the diet, had no significant effect on daily gain and feed-to-gain ratio compared with a level of 0 alfalfa meal; 40 or 60% alfalfa meal significantly depressed daily gain and efficiency of feed utilization compared with 0 or 20%. Backfat thickness was inversely related to level of alfalfa meal in the diet; cross-sectional area of the longissimus muscle was not affected by diet. Weight of the empty gastrointestinal tract (all segments except stomach) was increased with increasing fiber in the diet. Apparent digestibility of dry matter, cellulose, hemicellulose and nitrogen was progressively decreased with increasing fiber. Percentage of dry matter in digesta of all sections of the gastrointestinal tract was negatively correlated with cell wall content of diet and digesta. The lower dry matter of digesta of pigs fed high fiber was associated with a faster rate of passage and is suggested as being responsible for the lower digestibility of dry matter, nitrogen and cell wall components in pigs fed high fiber diets. Pigs slaughtered at 48 kg body weight had significantly higher apparent digestibility of dry matter, nitrogen and cell wall constituents than pigs slaughtered at 89 kg, probably due to the higher rate of passage of digesta in the heavier pigs. It is concluded that the depressing effect of fiber on apparent digestibility is due to the greater rate of passage of digesta in pigs fed high fiber and that there is no significant adaptation to high fiber diets with age during the growing-finishing period.