Longer storage length: What does it change? – Dr. Luiz Ferraretto, University of Florida
Ensiling is a well-established tool to store forages without compromising nutrient availability. The main goal during the ensiling process is to fill and seal silos rapidly to limit the amount of oxygen that enters the silo. After the silo is sealed and oxygen is removed, anaerobic bacteria use water-soluble carbohydrates as a substrate for fermentation and produce lactate and acetate. With the accumulation of these acids, silage pH drops until it reaches a stable phase where minimal changes occur until silo opening. This was generally accepted until some research trials, mainly from Delaware and Wisconsin, reported some alterations in the nutritive value of silage occur with extended storage length.
Generally, these studies reported that pH continues to decline due to the accumulation of lactate and acetate, although those effects are not as pronounced as the initial ensiling period. In addition, fermentation patterns may shift from lactate towards acetate, depending on the natural bacterial population in the silo or the microbial inoculant used at ensiling. Thus, these changes in fermentation patterns may mask the continuous effects of fermentation on pH drop and acid accumulation, or the changes are not large enough at the farm level.
But these studies with corn silage, high moisture corn and earlage consistently reported a gradual improvement in starch digestibility as fermentation progressed. In other words, allowing silage to ferment for longer periods of time increased the energy availability of the material.
In silage, starch granules are surrounded by prolamin proteins (insoluble proteins) that inhibit bacterial and enzymatic digestion of starch in the rumen and small intestine of dairy cows, respectively. Proteolysis is the main mechanism that disrupts this prolamin protein barrier and increases starch availability, and the acidic environment generated in the silo during fermentation aids in this process. This is confirmed by gradual increases in soluble protein and ammonia-nitrogen during fermentation across these studies.
However, in contrast, data from several sites across the country demonstrated that extended storage did not change, or even slightly reduced, NDF digestibility in corn silage.
Another potential effect of prolonged storage is a greater corn silage processing score (CSPS), or the percentage of starch passing through the 4.75-mm sieve, based on two experiments conducted in Wisconsin.
The first experiment reported a CSPS 10 percentage units greater for silage fermented for 30 days compared with unfermented material. The follow-up experiment reported a gradual increase in CSPS from 0 to 240 days of fermentation, similar to what commonly happens to starch digestibility, ammonia-nitrogen and soluble crude protein. But the extent of increase in CSPS was of a lower magnitude than the first experiment. Perhaps the magnitude of the CSPS change as fermentation progresses is dependent upon the initial values of unfermented samples or other factors and more research is warranted.
But these findings highlight the potential effects of extended fermentation, not only in chemical, but also physical characteristics of kernels. However, prolonged storage length will not replace adequate processing at harvest.
In summary, research supports the use of inventory planning so a newly harvested crop would be fed only after three to four months in storage. Although prolonged storage of corn silage would be a valid management practice, it requires proper silo management during filling, packing and covering to ensure beneficial fermentation patterns.
Forage storage and management