Interactive effects of molasses by homofermentative and heterofermentative inoculants on fermentation quality, nitrogen fractionation, nutritive value and aerobic stability of wilted alfalfa (<i>Medicago sativa L</i>) silage

Abstract

The effect of adding molasses (0, UM or 50 g/kg on DM basis, M) and two types of inoculant including homofermentative (HO) and a combination of homofermentative and propionate-producing bacterial (HOPAB) inoculants on silage fermentation quality, nitrogen fractionation and aerobic stability of pre-bloom, wilted alfalfa (AS) was determined in laboratory silos. The HOPAB inoculant was more effective than HO in reducing the alfalfa silage pH but increased propionate content in the absence of M (p < 0.05). Inoculation of HOPAB reduced (p < 0.01) acid detergent fibre (ADF) and increased (p < 0.01) lactate to acetate ratio compared with uninoculated AS. Acetate concentration was lower (p < 0.01) in HOPAB-inoculated than other AS. This difference was more pronounced in M-added AS (inoculants × M interaction, p = 0.01). Both inoculants reduced (p < 0.01) ammonia-N content in AS added with M, whereas only HOPAB decreased (p < 0.01) ammonia-N concentration in silage without M. Inoculants increased (p < 0.01) B2 fraction in AS with M addition but had no effect on AS without M. Treating silages with HO-UM increased (p < 0.05) C fraction (acid-detergent insoluble-N) but HOPAB decreased C fraction at two levels of M. Treating alfalfa crop with M and HOPAB improved aerobic stability by increasing the concentration of acetate and propionate of AS respectively. Adding M tended (p < 0.10) to increase short-chain fatty acids (SCFA) and cumulative gas production (CGP). HOPAB alone increased DM disappearance at 24 h post-incubation and effective degradability assuming outflow rate of 8%/h relative to untreated AS (p < 0.05). It was concluded that adding M had no pronounced effects on AS fermentation quality, but increased aerobic stability. HOPAB-inoculated AS with no addition of M improved fermentation quality and increased DM degradability compared with HO.