Microscopy and protein solubilization of digesta from pigs fed wheat, corn, or soybean meal-based diets, with or without protease and a Bacillus spp. direct-fed microbial

摘要

Two types of microscopy were used to visualize the microstructure of ileal digests from grower pigs fed corn, wheat or SBM (soybean meal)-based diets. Digests were incubated with a Bacillus spp. DFM (direct-fed microbial) and a protease. Microscopy images were taken before and after the incubations. A protein solubilization assay was performed to provide supporting quantitative data. The aim was to visualize differences between the undigested fractions of the different ingredients, and observe whether a protease and DFM combination could increase degradation of this fraction. Heal digesta was obtained on d 5-7 from one pig fed diets based on corn, wheat or SBM from a study where eight ileal cannulated barrows (30 kg) were fed a total of 8 different diets for 7 d in an 8 x 8 Latin Square design. Digests samples were incubated with no additive (control), DFM (3.3 x 10(5) cfu/g digests), protease (11 U/g digesta), or DFM + protease. The supernatant and pellet were separated by centrifugation and used to observe internal and external microstructure and quantify protein solubilization. In images from confocal laser scanning microscopy and scanning electron microscopy, it appeared that there were differences in nutrient structure of the ingredients and the digests. Wheat and corn appeared to have many protein starch interactions whilst SBM had mostly protein-fiber interactions. The microscopy indicated that the protease and DFM had a complementary effect in degrading the fiber-protein complexes in the SBM-based digesta, which was supported by an increase in protein solubilization with the additive combination compared to the control (1635 vs. 730 ng/mu L; P = 0.02). This may be due to a complementary mode of action involving hydrolysis of proteins by protease giving increased access to fiber substrates for DFM secreted enzymes to act upon. However, the additives had no effect on protein solubilzation from wheat and corn-based digests (wheat; 2022 vs. 1063 ng/mu L; P = 0.44, corn; 1162 vs. 854 ng/mu L.; P = 0.73), and it is not possible to conclude the efficacy or mode of action of the additives in wheat and corn from qualitative microscopy images alone. The results illustrate key differences in the structures and undigested substrates of the ingredients, and mode of action for the combination of protease and DFM in SBM-based digests, supporting previously published in vivo data. Further investigation is required to validate the in vitro efficacy and mode of action of the feed additives on wheat and corn-based digesta.