Ileal Amino Acid and Phosphorus Digestibility of Fermented Corn–Soybean Meal Mixed Feed with Bacillus Subtilis and Enterococcus Faecium Fed to Pigs

In the present study, a 2-stage solid-state fermentation (TS-SSF) process using Bacillus subtilis followed by Enterococcus faecium was carried out with the purpose of improving the nutritional quality of corn and soybean meal mixed feed (MF). The matrix of native MF and fermented mixed feed (FMF) was analyzed using scanning electron microscopy to determine external structures during solid-state fermentation. Results of the present study indicated that the FMF contained a greater concentration of CP and total P compared with the unfermented feed, whereas the contents of β-conglycinin, glycinin, phytate P, and NDF in FMF declined by 77.6, 86.7, 41.2, and 38.9%, respectively. It is worth noting that the content of trichloroacetic acid–soluble protein, particularly those of small peptides and free AA, increased more than 3 times after TS-SSF. Scanning electron microscopy revealed that irregular shapes and rough surfaces were mainly observed in FMF whereas the microstructure of untreated MF was regular and the surface was smooth. Two animal experiments were conducted to evaluate the digestibility of CP and P in FMF when fed to pigs. In Exp. 1, 6 barrows (15.20 ± 1.27 kg initial BW) fitted with a T-cannula in the distal ileum were allotted to a 3 × 3 Latin square with 3 diets and 3 periods per square. Two diets containing unfermented MF or FMF as the only source of protein and a N-free diet were formulated. Results indicated that the apparent ileal digestibility of 6 indispensable AA (Arg, Ile, Leu, Lys, Met, and Thr) and 2 dispensable AA (Ala and Gly) in FMF were greater (P < 0.05) than in untreated MF. The standardized ileal digestibility of 4 AA (Ile, Leu, Lys, and Ala) in FMF was also greater (P < 0.05) than in MF. In Exp. 2, 16 barrows (17.57 ± 1.08 kg initial BW) were allotted to 2 diets formulated to contain MF or FMF as the sole source of P to determine the digestibility of P. The apparent total tract digestibility and standard total tract digestibility of P in FMF were 58.14 and 64.72%, respectively. These values were greater (P < 0.01) than in untreated MF (37.11 and 44.89%, respectively). Our results suggest that the TS-SSF process using B. subtilis followed by E. faecium offers an effective approach to improving the quality of corn and soybean meal MF.