Effects of an exogenous protease on the fermentation and nutritive value of corn silage harvested at different dry matter contents and ensiled for various lengths of time

摘要

The objective of this experiment was to evaluate the effects of adding an experimental protease to corn plants harvested at different maturities on silage fermentation and in vitro ruminal starch digestibility (IVSD). Corn plants were harvested at maturities resulting in plants with 31 or 40% dry matter (DM). Plants were chopped, kernel processed, and treated with (1) only a 0.1 M phosphate buffer (pH 5.5, 5% vol/wt of fresh forage), (2) buffer with protease to obtain a final concentration of 20 mg of protease/kg of wet forage, and (3) buffer with protease to obtain a final concentration of 2,000 mg of protease/kg of wet forage. Treated forages (about 500 g) were ensiled in nylon-polyethylene pouches and stored between 21 and 23℃ for 0, 45, 90, and 150 d. Data were analyzed as a 2 × 3 × 4 factorial arrangement of treatments, with the main effects of harvest DM, dose of protease, days of ensiling, and their interactions. The treatment with the highest dose of protease resulted in more robust fermentations across harvest DM with higher concentrations of lactic and acetic acids compared with untreated silage. Concentrations of soluble protein (% of crude protein) increased with time of ensiling, regardless of DM content at harvest. However, averaged over both harvest DM contents, it increased by 37% for silages treated with the high dose of protease compared with an average 11% increase for untreated silages and silage treated with the low dose of protease, between d 0 and 45. Averaged over both harvest DM contents, the concentration of soluble protein peaked in silages treated with the high dose of protease after 45 d of ensiling, whereas it peaked at d 90 in untreated silages and silage treated with the low dose of protease. Similar changes occurred in the concentration of NH_3-N due to length of ensiling and treatment with protease. In fresh forages, the concentration of starch for early- and late-harvested forages was similar, but IVSD was lower in the latter. After 45 d of ensiling, IVSD was highest in both early- and late-harvested silages that were treated with the high level of protease. After 150 d of ensiling, IVSD was similar among silages treated with protease, regardless of DM at harvest. Treating corn plants with a high dose of an experimental protease at harvest accelerated proteoly-sis during ensiling, resulting in corn silages with levels of IVSD after 45 d of ensiling that were only obtained in untreated corn silages after 150 d of ensiling.