The effects of an exogenous protease on the fermentation and nutritive value of corn silage and high moisture corn

The objective of this dissertation was to further evaluate the potential of adding an exogenous protease to whole plant corn or high moisture corn at harvest on the subsequent silage fermentation and the ability to improve in vitro ruminal starch digestion. Several experiments were conducted to achieve this objective. The protease used in all experiments was an experimental formulation that expressed high activity at low pH. All plant material was ensiled in laboratory-scale bag silos and ensiled at 22-23°C. In all experiments, treatment with 2000 mg of protease per kg of wet forage resulted in increases in the indices of proteolysis over untreated silages, which were increased soluble protein and NH3-N. These changes were accompanied by improvements in 7 h in vitro digestibility of starch over untreated silages. Treatment with protease had no effects on total essential or non-essential amino acids, or total amino acids in corn silage although there were changes in individual amino acids. In experiments with corn silages, soluble protein was more highly correlated with starch digestion than was NH3-N. In three of the four experiments conducted with corn silage, treatment with 2000 mg of protease per kg of wet forage resulted in higher concentrations of ethanol and yeasts compared to untreated silage. However, those experiments were conducted before a robust dose titration experiment had been completed. In that experiment, treatment with 200 mg of protease/kg of wet forage was sufficient to improve the in vitro digestibility of starch and had no adverse affects on concentrations of starch or numbers of yeasts. The improvement in starch digestion from 200 mg/kg was similar to higher dose levels of protease through 2000 mg/kg. Treatment with protease was equally effective in improving starch digestion in well- versus poorly-processed corn silage and in low (31%) versus high DM (40%) corn silages. Use of an exogenous protease also improved starch digestion in high moisture corn. In contrast to corn silage, NH 3-N was as highly correlated to starch digestion, as was soluble protein for high moisture corn. Overall, the experiments conducted for this dissertation showed that adding an exogenous protease at the time of ensiling to high moisture corn and corn silage may be a method to increase starch digestion in a relatively short period of ensiling (45 d) rather than waiting for this to occur naturally, which would require a more prolonged length of ensiling (several months). Although high concentrations of added protease (2000 mg/kg) appeared to have some potential negative effects on silage fermentation (higher ethanol and more yeasts), a lower dose (200 mg/kg) was as effective in improving digestion as higher doses but without these complications.