Effects of malate, citrate, succinate and fumarate on fermentation, chemical composition, aerobic stability and digestibility of alfalfa silage

This study was to evaluate the effects of malate, citrate, succinate and fumarate on the fermentation quality, proteolysis and lipolysis and aerobic stability of alfalfa silage ensiled at two different dry matter (DM) contents. Alfalfa was harvested in the late bud to the early flower stage and wilted to DM contents of approximately 330 (normal DM) and 400 (high DM) g/kg fresh weight. The wilted and chopped alfalfa was ensiled in vacuum-sealing polyethylene plastic bags with treatments of control (distilled water), 0.5 % DL-malic acid (MA), 0.5 % citric acid (CA), 0.5 % sodium succinate (SS) and 0.5 % sodium fumarate (SF). All the application rates were based on the fresh weight of forage. After 60 days of ensiling, alfalfa silages ensiled at a normal DM had greater concentrations of lactic acid, acetic acid, non-protein N (NPN), ammonia N (NH3-N), greater aerobic stability and lower concentration of water soluble carbohydrates (WSC), DM loss when compared to the silages ensiled at a high DM (P < 0.05). These four additives had positive effects on increasing the concentrations of lactic acid and WSC in treated silages ensiled at two different DM contents but the lower pH was only observed in MA and CA-treated silages. Unlike the lower concentrations of acetic acid in MA and CA-treated silages, SS and SF-treated silages with a normal DM had greater acetic acid. Application of these four additives reduced the concentration of NPN and NH3-N in treated silages (P < 0.05) and the lowest concentrations of NPN and NH3-N were observed in MA and CA-treated silages with a high DM content. Application of MA, CA and SS reduced the aerobic stability of ensiled alfalfa with normal DM content but CA and SF improved aerobic stability of the silage with high DM content. In addition, MA and CA increased in vitro dry matter digestibility (IVDMD) at two different DM contents but no effects were found in SS and SF treatments. Application of MA and CA led to higher polyunsaturated fatty acid (PUFA) proportions in ensiled alfalfa at a normal DM than those in the control silage (P < 0.05). Moreover, greater residues of MA, CA and succinic acid were observed in treated silages except for comparable MA in SS and SF-treated silages. However, no fumaric acid was observed in ensiled silages. These results indicate that including MA and CA could improve silage fermentation quality and digestibility, limit proteolysis and lipolysis and DM loss. However, little effect was observed in SS or SF treatments.