Influence of microbial inoculation and length of storage on fermentation profile, N fractions, and ruminal in situ starch disappearance of whole-plant corn silage

Abstract

Increasing the length of storage of whole-plant corn silage (WPCS) has been shown to increase ruminal in vitro starch digestibility by facilitating hydrolysis of the protein matrix surrounding starch granules. It is possible that microbial inoculants could improve fermentation, thereby enhancing proteolytic activity in the silo. Additionally, microbial inoculants have potential to reduce or prevent the growth of toxigenic fungi in silage. Therefore, the objective of this study was to determine the effects of storage length and microbial inoculation with heterofermentative and homofermentative inoculants containing Enterococcus faecium on the fermentation profile, N fractions, and ruminal in situ starch disappearance of whole-plant corn silage, as well as the effect of microbial inoculation on silage mycotoxin concentrations. Whole-plant corn (333 ± 10 g of DM/kg as-fed) was ensiled in quintuplicate vacuum pouches untreated (CON) or after the following treatments: E. faecium at 1.5 × 105 cfu/g (EF); Lactobacillus plantarum at 1 × 105 and E. faecium at 5 × 104 cfu/g of fresh forage (LPEF); and L. buchneri and Lactococcus lactis at 1.5 × 105 cfu/g (LBLL). Silos were stored for 0, 30, 60, 90 or 120 d. Silage pH was greater with LBLL compared to the other three treatments (P = 0.005). Total acids were greater with LPEF than EF (P = 0.005). Ammonia-N (expressed as g/kg of N) was greatest with CON compared to the other treatments (P = 0.001). Concentrations of lactic acid were lower, and concentrations of acetic acid were greater with LBLL compared to the other treatments (P = 0.001). An interaction between microbial inoculation and storage length was observed for soluble CP concentrations as well as ruminal in situ starch disappearance (P = 0.001 and P = 0.012, respectively). Soluble CP (expressed as g/kg of CP) was greater with CON compared to the other treatments at d 30 and 90, but not different at d 60 and 120. Ruminal in situ starch disappearance was reduced for CON compared to the other three treatments at d 60 and 90. However, at d 120, ruminal in situ starch disappearance was similar across all treatments. Overall, the use of microbial inoculants improved fermentation profile. Microbial inoculation also increased starch disappearance in the earlier stages of fermentation but by 120 d of storage, starch disappearance was similar between inoculated silage and CON. Results from this study failed to support the hypothesis that microbial inoculants would reduce mycotoxin contamination.