Effect of exogenous protease enzymes on the fermentation and nutritive value of corn silage

摘要

The objective of this study was to evaluate the effects of adding experimental formulations of exogenous protease enzymes on the fermentation and nutritive value of whole-plant corn ensiled in laboratory silos. Chopped and processed whole-plant corn (36.8% DM) was ensiled without enzymes or treated with 1 of 2 experimental proteases (E85 or E86; AB Vista, Wiltshire, UK) at 20 or 2,000 mg/kg (wet-weight basis). Forages were packed in vacuumed and heat-sealed bags and ensiled for 45 and 150 d at 23 ± 1℃. When compared with untreated silage, addition of proteases and length of ensiling time had no effect on silage pH or concentration of crude protein. The results were similar for the concentrations of acid detergent fiber, neutral detergent fiber, and starch, although protease x time interactions were observed for these components, which were biologically minor. When compared with untreated silages, only treatment with the 2,000-mg/kg application amount of E85 resulted in lower neutral detergent fiber after 45 d of ensiling. Proteases did not affect NDF digestibility after 150 d of ensiling when compared with untreated silage. Similarly, treatment with enzymes did not affect the concentrations of lactic and acetic acids or ethanol when compared with untreated silage. Concentrations of NH_3-N and soluble protein (% of crude protein) increased with storage time compared with concentrations at harvest and were greater for the 2,000-mg/kg doses of proteases when compared with untreated silage at both 45 and 150 d. In vitro ruminal digestibility of starch after 7 h of incubation was 66.3% for freshly chopped corn plants. After 45 d of ensiling, starch digestion was greater for E86 applied at the 2,000-mg/ kg dose (80.6%) than in all other treatments, with the exception that it was similar to the 2,000-mg/kg dose of E85. After 150 d of ensiling, the 20-mg/kg dose of E85 (81.9%), the 2,000-mg/kg dose of E85 (82.9%), and the 2,000-mg/kg dose of E86 (88.6%) had greater starch digestibility than untreated silage (74.0%). To the best of our knowledge, this is the first study to show that addition of exogenous proteases added to corn forage at the time of harvest can increase in vitro ruminal starch digestibility during silage fermentation. Data suggests that adding exogenous sources of protease enzymes at ensiling may be a method to obtain a high degree of ruminal starch digestibility in corn silage that would normally require longer periods of time to obtain from prolonged storage.