For many years, it was believed that the ensiling process involved ensiling, fermenting and, after reaching low levels of pH and high levels of lactic and acetic acid, the ceasing of fermentation. And the forage material would maintain its nutritive value for as long as the silo remained closed.
Recently, research was conducted to understand how ensiling time affects nutrients. The studies concluded that fermentation never stops, but rather continues, just at a slower pace. There isn't a drastic drop in pH or a drastic increase in other acids as fermentation continues to progress.
When evaluating starch digestibility, studies indicate that starch becomes much more digestible in the spring than it is in the fall.
"The same bacteria that produce different acids to help the fermentation process also produce enzymes that break down proteins that surround starch, making the starch more available. That's why we see higher levels of soluble proteins as well as higher levels of digestible starch during the spring," said Luiz Ferraretto, assistant professor at the University of Florida. "A longer ensiling process could be used as an alternative to improve the nutritive value of forages."
Producers who have enough land to maintain a higher silage inventory than they can use in a year will be rewarded in nutritive value for allowing an extra three or four months of fermentation rather than opening 20 or 30 days after ensiling.
"If you start comparing spring milk fat tests with fall milk fat tests, they're normally lower," he said. "We are reaching February and going into March, so it's a good time to collect some samples in the silo and analyze them for in vitro starch to see if they are more digestible, which may cause milk fat depression."
The research raises the question of whether waiting longer to open your silo can fix other issues that are known to decrease starch digestibility in silage.
A study was conducted ensiling corn harvested with low maturity and comparing it with corn harvested at late maturity. Normally, it would be expected that the late maturity corn would have more starch but be less digestible. So, if the late maturity corn could ferment longer, would the silage reach similar digestibility?
"We found that if you allow both silos, early maturity and late maturity, to ferment ... longer, the silage did not reach similar digestibility," Ferraretto said. "Both will increase their starch digestibility over time, but in exchange you can open your early maturity silage first and the late maturity silage later. This will give the silo more time to ferment, so it will decrease the difference between the two."
A longer fermentation is always better, but it also comes with the potential for external traps to open the silo. For example, animals walking above the silo could make holes in the plastic. Therefore producers must check it more frequently.
"If you don't have proper conditions for fermentation, you won't see the benefit," he said. "Allowing silage to ferment longer is an investment, so you want to ensure the entire process goes well."