Four experiments were conducted to evaluate the nutritional value of dehulled solvent-extracted soybean meal (SBM-CV), fermented SBM-CV (F-SBM), dehulled full-fat soybeans (FFSB), and F-FFSB. The fermentation process increased the protein content by approximately two percentage units and decreased the stachyose and raffinose content to near zero in the F-SBM and F-FFSB. In Experiments 1 and 2, two precision-fed rooster assays were performed to determine the nitrogen-corrected true metabolizable energy (TMEn) and standardized amino acid (AA) digestibility among the test ingredients using conventional and cecectomized roosters, respectively (6 roosters per treatment, fed 25 g). Dietary treatments were arranged in a 2 × 2 factorial to evaluate the effects of fermentation and SBM type, and the data were analyzed as a two-way ANOVA with alpha set at P<0.05. There was an interaction (P<0.05) between fermentation and SBM type for TMEn. Fermentation of SBM-CV increased TMEn, while fermentation of FFSB decreased TMEn. There was no main effect of fermentation or SBM type for indispensable AA digestibility values except for Lys, where a negative effect (P<0.05) of fermentation was observed. In Experiment 3, an ad libitum-fed broiler chicken assay was conducted to determine apparent ileal P digestibility and total tract P retention at two Ca levels among the 4 test ingredients. Diets contained a Ca:non-phytate P ratio of either 2 or 7.5. Dietary treatments were arranged in a 2 × 2 × 2 factorial with fermentation, SBM type, and Ca level as the main effects (5 pens of 5 chicks per diet). Data were analyzed as a three-way ANOVA with alpha set at P<0.05. Higher (P<0.05) apparent ileal P digestibility values were observed at the lower Ca level than at the higher Ca level. At the higher Ca level, fermentation increased ileal P digestibility and total tract P retention for both conventional and full-fat samples. Experiment 4 was conducted to determine relative P bioavailability (RBV) of the test ingredients compared with KH2PO4 using crossbred chicks (5 pens of 5 chicks per diet). Multiple regression of bone ash (mg/tibia and %) on supplemental P intake yielded slope-ratio RBV varying from 23% to 48%. Fermentation did not significantly affect RBV of P in SBM-CV, but increased (P<0.05) RBV of FFSB.
In summary, fermentation increased TMEn in SBM-CV but had a negative effect on Lys digestibility for both SBM-CV and FFSB, suggesting possible heat damage during the fermentation process. Fermentation had a positive effect on apparent ileal P digestibility and total tract P retention for both SBM-CV and FFSB when diets contained 0.75% Ca and also increased RBV of P in FFSB based on bone ash responses in chicks.
