Case Study: Microbial inoculant and ensiling time effects on fermentation profile, nitrogen fractions, and ruminal in vitro and in situ starch digestibility in corn shredlage and late-maturity corn silage

Abstract

Two experiments were conducted to evaluate the effects of ensiling time and microbial inoculation on N fractions and starch digestibility in either well-processed corn shredlage (SHRD; Exp. 1; 76% of starch passing through a 4.75-mm screen, 39.3% DM, and 32.2% amylase-treated NDF) or late-maturity corn silage (Exp. 2; 48.0% DM and 22.9% amylase-treated NDF). For Exp. 1, unfermented SHRD was allocated into 24 samples of 600 g each and randomly assigned to 6 treatments in quadruplicate. Treatments were a combination of SHRD noninoculated (CON) or inoculated at the recommended inoculation rate (1X; 5 × 104 cfu of Lactobacillus plantarum, Lactobacillus casei, Streptococcus faecium, and Pediococcus per gram of fresh whole-plant corn) or twice the recommended inoculation rate (2X; 10 × 104 cfu/g of fresh whole-plant corn) of a microbial inoculant and ensiled for 30 or 120 d. Exp. 2 used the same experimental methodology except for evaluating treatments within late-maturity corn silage rather than SHRD. In Exp. 1, DM and starch concentrations were unaffected by treatments. Although not affected by inoculation, content of CP increased from 30 to 120 d of ensiling. Measurements of pH were reduced from 3.96 at 30 d to 3.88 after 120 d. Concentrations of lactate and ethanol were similar but acetate and total acids were greater after 120 d. Ammonia-N concentration and starch digestibility increased from 30 to 120 d. Fermentation profile, including ammonia-N, and starch digestibility of SHRD were unaffected by inoculation. In Exp. 2, ensiling time did not affect concentrations of DM, CP, and starch. However, DM and starch contents were 2.5 and 3.4 percentage units greater for 2X than other treatments. Concentrations of lactate and total acids were greater for CON and 1X than 2X. Propionate and ethanol concentrations tended to be greater for CON than other treatments. Despite the lower ammonia-N concentration for 2X, starch digestibility was unaffected by microbial inoculation. Greater lactate, acetate, and total acid concentrations after 120 d of ensiling were observed. Reductions in pH and ethanol concentration were also observed for 120 d compared with 30 d. Late-maturity corn silage fermented for 120 d had greater ammonia-N (5.4 vs. 4.0% of CP) and starch digestibility (66.7 vs. 61.7% of starch) compared with 30 d. Ammonia-N concentration and starch digestibility were greater after 120 d of fermentation in both experiments, suggesting that extended ensiling time is advantageous in both scenarios. Inoculation with lactate-producing bacteria, however, did not improve starch digestibility in either experiment.