Abstract
Ninety nursery pigs were used in two metabolism experiments to determine the effects of roasting and extruding on the nutritional value of Williams 82 soybeans with (+K) and without (-K) gene expression for the Kunitz trypsin inhibitor. Treatments for both experiments were: 1) soybean meal; 2) +K roasted; 3) +K extruded; 4) -K roasted; and 5) -K extruded. Diets were the soybean preparations (96.5% of the diet) with only vitamins and minerals added as needed to meet or exceed NRC recommendations. Daily feed allowance was 5% of initial BW given as three equal meals. In Exp. 1, 50 weanling pigs (4.7 kg average BW and 21 d average age) were used. Apparent values for N digestibility (p<0.001), biological value (p<0.09), percentage N retention (p<0.05), GE digestibility (p<0.001) and percentage ME (p<0.001) were greater for pigs fed extruded soybeans than pigs fed roasted soybeans. Also, N digestibility (p<0.05), biological value (p<0.03) and percentage N retention (p<0.04) were greater for pigs fed -K soybeans than those fed +K soybeans. In Exp. 2, 40 pigs (9.7 kg average BW and 35 d average age) were allowed to adjust to the nursery environment before use in the experiment. In general, the pigs in Exp. 2 (i.e., the older pigs) had greater utilization of nutrients from all of the soybean products than the younger pigs used in Exp. 1. Digestibilities of DM, N and GE were greater (p<0.001) for pigs fed -K soybeans than those fed +K soybeans and extruded soybeans had greater digestibilities of DM, N and GE than roasted soybeans (p<0.001). Also, percentage N retention (p<0.01) and percentage ME (p<0.001) for pigs fed extruded soybeans were greater than for pigs fed roasted soybeans. In conclusion, extruded and -K soybeans were greater nutritional value than roasted and +K soybeans for 4.7 and 9.7 kg nursery pigs.