Corn silage: What happens while it sits in storage?

By Marin Western, Vita Plus dairy specialist

“How long do we need to wait before we break into the new corn silage?”

I get asked this question each fall.  Luckily, here in Michigan, inventories have continued to build the last few forage seasons and, as a result, we have seen increased carryover.  However, it is always a good idea to remember why we suggest the typical “wait periods” that we do.

Fermentation has four phases.  In phase 1, we fill the silo and this phase will continue until oxygen is depleted from the silage. As we fill a bag, bunker, pile, or upright silo, plant enzymes break down sugars to carbon dioxide, water, and heat. While oxygen is in the silage, spoilage organisms like yeasts, molds, and bacteria also break down sugars or water-soluble carbohydrates. Prolonged oxygen exposure increases the presence of yeasts and molds and, once they enter, they will always be in the silage.  Ideally, phase 1 is short to decrease energy and dry matter (DM) loss.

Phase 2 begins once oxygen is depleted and anaerobic bacteria start their portion of the fermentation process. Anaerobic simply means “without oxygen” and these bacteria transform water-soluble carbohydrates into acetic acid. This is an inefficient fermentation process and, when lengthy, can lead to DM losses and a potential for lower lactic acid production needed for stability.

Phase 3 is also anaerobic process, but a different group of bacteria – called homofermentative lactic acid bacteria – take over the fermentation. These are the only bacteria that produce lactic acid needed to lower the pH of the silage.

Phase 4 begins once the silage reaches a pH of 4.5 or lower.  The silage will stay in this stable state until feedout begins or oxygen or water is introduced to the silage.

The progression of all four phases depends on management practices, including how silos are filled, silage DM and the kind of silage. For example, haylage can complete a fermentation process in just 21 days.

Corn silage is a different for one main reason…corn kernels! We know that kernels – and how easily the cows can digest them – are especially important for production and a farm’s bottom line. Each kernel has a starch-protein matrix made of starch, prolamins and other proteins on the outside of each starch granule.  The matrix acts like glue, limiting digestibility of starch. Prolamins are storage proteins that must be broken down in corn silage to increase starch digestibility.

Prolamins can break down as the silage sits in phase 4 of fermentation, increasingly improving starch digestibility as time progresses.  That’s why the general rule of thumb is to let corn silage sit for at least three months after ensiling.

As we wrap up a successful 2021 silage season in most of the Midwest, many are starting to plan ahead for the next forage season. Work with your team to develop a forage plan to ensure proper inventories to get the most out of your feed.