Abstract The objective was to test the hypothesis that feeding intact protein from soybean meal (SBM) to growing pigs, instead of combinations of SBM with crystalline amino acids (AA) or co-products including corn distillers dried grains with solubles (DDGS) or high-protein DDGS (HP-DDGS), results in greater nitrogen retention, digestible energy (DE), and metabolizable energy (ME). Six diets were formulated. Two diets contained corn and 31% SBM or corn and 21% SBM and crystalline AA. Four additional diets contained corn, SBM, and DDGS, or corn, SBM, and HP-DDGS, without or with supplementation of Trp, Val, and Ile to ameliorate the negative effects of excess Leu in corn co-products. A total of 48 pigs (initial weight: 39.91 ± 3.90 kg) were allotted to the six diets in a randomized complete block design. Pigs were housed individually in metabolism crates. Feces and urine were quantitatively collected for four days after seven days of adaptation. The apparent total tract digestibility (ATTD) of energy, concentrations of DE and ME, and nitrogen balance were calculated. The statistical model included diet as fixed variable and block and pig withing block as random variable. Pairwise comparisons were used to separate the means. Results indicated that the ATTD of dry matter, energy, and nitrogen were greater (P 0.05) for pigs fed SBM diets than for pigs fed DDGS or HP-DDGS diets (Table 1). Absorbed nitrogen was greater (P 0.05) in pigs fed the diet with 31% SBM compared with pigs fed all other diets. Retained nitrogen (g/d) was reduced (P 0.05) in pigs fed the low-SBM diet or the HP-DDGS diet with added AA compared with pigs the high-SBM diet or the DDGS diet with added AA. The DE and ME were greater (P 0.05) in SBM and HP-DDGS diets compared with DDGS diets, regardless of AA in the diets. In conclusion, feeding SBM increased daily nitrogen retention and provided greater DE and ME compared with DDGS diets, indicating that supplementation of Ile, Val, and Trp to diets containing corn coproducts did not fully compensate for the reduced nitrogen and energy digestibility and reduced nitrogen retention in pigs fed these diets, which may be a result of excess Leu in corn-coproducts. In contrast, feeding a low-SBM diet with crystalline AA to pigs reduces daily nitrogen retention.
Ibagon et al. (Wed,) studied this question.