Roasting and extruding affect ileal digestibility of nutrients from soybeans in growing and finishing pigs

Abstract

Eight crossbred barrows (initial body wt of 90 lb and 180 lb for four growing and four finishing pigs, respectively) were fitted with T-cannulas at the distal ileum and used in 36-d metabolism experiments (4 x 4 Latin squares) to determine the effects of roasting and extruding full-fat soybeans on nutrient utilization. Treatments were 1) soybean meal, 2) roasted soybeans, 3) extruded soybeans, and 4) soybeans extruded with an extrusion enhancer (sodium sulfite). The soybean meal and soybeans were mill-run. The control diet was cornstarch-based, with .9% lysine, .65% Ca, and .55% P for the growing pigs and .75% lysine, .55% Ca, and .45% P for the finishing pigs. For the growing pigs, apparent total tract digestibilities of DM and GE were greater for soybean meal than full-fat soy products. However, ileal digestibilities of DM, GE, N, and amino acids generally were greatest for extruded soybeans and lowest for roasted soybeans, with soybean meal intermediate. Differences at the terminal ileum were more pronounced than for the total tract, thus indicating that hind-gut fermentation is likely to mask many of the true nutritional differences in feedstuffs. For finishing pigs, total tract digestibilities of DM and GE were greater for soybean meal than for the full-fat soy products because of the relatively low digestibility coefficients for roasted soybeans. Ileal digestibilities of DM, GE, and N were greater for the extruded soybeans and extruded soybeans with sodium sulfite than for the roasted soybeans. Availabilities of the indispensable amino acids measured at the terminal ileum were greatest for extruded soybeans, intermediate for soybean meal, and lowest for roasted soybeans. In conclusion, nutrient digestibilities and availabilities of indispensable amino acids tended to be greatest in extruded soybeans, intermediate in soybean meal, and lowest in roasted soybeans for growing and finishing pigs.