Hold off opening that silage bunker

Nothing’s more exciting than opening a corn silage bunker to see how this year’s crop turned out. OK, so maybe there are a few things that might be more exciting.

Most milk producers, though, are anxious to begin anew with just-harvested corn silage — too much so. All too often, that bunker is opened long before it has had time to completely ferment.

Key Points

Let corn silage ferment at least four to five months if at all possible.

Soluble protein and starch digestibility improve with time.

This is another reason why farms with feed reserves produce more milk.


So for months, you might feed corn silage somewhere between greenchop and fermented. The result is reduced milk yield, disastrous milk-fat tests and cows on the edge of ruminal acidosis.

Why it pays to wait

Cumberland Valley Analytical Services recently analyzed the impact of storage on soluble protein and in-vitro starch digestibility of 2009 corn silage. They concluded that the fermentation process often doesn’t stabilize until four to five months after ensiling.

In other words, soluble protein and starch digestibility continue to improve over those four to five months. By opening silos earlier, we introduce oxygen and can alter that fermentation and promote the growth of molds, yeasts and other spoilage organisms.

That may be another reason why dairy farms with hefty silage reserves often have higher-producing cow herds.

So what do you do if you must begin feeding corn silage before it’s completely fermented? First, I recommend keeping the silo sealed for as long as possible. Ideally, that’s at least six to eight weeks. Even an extra week can improve silage stabilization.

Then the balancing act begins. Feed-out of new corn silage needs to be fast enough to maintain a good, clean bunker face, yet slow enough so large amounts of corn silage aren’t exposed to oxygen.

To aid in the cow’s adjustment to the new corn silage, it’s a good idea to mix last year’s corn silage with new crop silage. For that first week, mix 75% old to 25% new. For the second week, switch to 50-50, old to new.

For week three, go to 25% old corn silage to 75% new. By week four, you can go 100% new crop silage. While you’re making these changes, the rest of the diet must compensate for your cows’ production needs.

Ration-balancing becomes crucial

Prior to making shifts in corn silage, decrease dietary starch content to no more than 23% starch (dry matter basis). Increase physically effective neutral detergent fiber, or peNDF, to 23 to 25% of diet DM.

Fermentable NDF sources work well in stabilizing rumen pH. Citrus pulp works very well with high corn-silage diets. Beet pulp tends to work better with high hay-crop silage diets. Soy hulls work well with both forage bases.

Throughout the silage transition, top dressing or adding dry hay to the diet will also help meet the peNDF needs and keep cows chewing their cuds. While I’ve had mixed results with free-choice sodium bicarb, additional access to bicarb may help with forage transitions. I prefer, however, to increase it in the total mixed ration.

Watch cows’ manure for bicarb needs. Loose, bubbly manure indicates ruminal acidosis, and a need for more peNDF and more bicarb. Watch fresh cows and heifers for edema when increasing dietary bicarb.

Testing forages for dry matter weekly, and often daily, is merited when feeding incompletely fermented corn silage. Yes, that sounds extreme. But silage dry matter and other nutrient composition will change daily as you work your way into the silo, especially if it was opened after only a few weeks of fermentation.

I also suggest sampling that corn silage monthly for the first six months. Running a wet chemistry analysis will tell you much about the changes going on in soluble proteins and starch digestibility.

Carson and husband Steve partner in Harkdale Farms of Newbury, Vt. She’s also a professor at Vermont Technical College.

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MONEY-LOSING STARTS HERE: Corn silage really needs four to five months of fermentation to make the best feed and the most milk.

This article published in the November, 2010 edition of AMERICAN AGRICULTURIST.

All rights reserved. Copyright Farm Progress Cos. 2010.