Corn-silage quality is optimized if the crop remains in storage for three to four months before it's fed, say dairy nutritionists.

Corn silage goes through four phases, with the final phase offering the best-quality feed, says Mike Hutjens, University of Illinois extension dairy nutritionist.

“You can feed it green right off the field or you can feed it four to seven days after it's been ensiled in a bunker, upright silo or bag,” says Hutjens. Fermentation is complete within a week after harvest.

“Or you can feed it three to four weeks after ensiling, which offers better-quality feed than the first two options. But for the best silage, ensile it for three to four months before using it. That's why many dairy producers see a spike in production after the holidays,”says Hutjens.

David Atwell, a dairy nutritionist and management consultant for Ag Partners in southeastern Minnesota and western Wisconsin, concurs.

“During storage, the starch component (grain) of the silage becomes more digestible,” Atwell notes. “The starch is initially encapsulated within a protein matrix, which gets broken down.”

But if you're not able to wait that long, the silage still works, they say.

“It's fine early on,” says Atwell, who recommends adding a little more grain to the ration to compensate for the lower digestibility. “But those extra three to four months in storage make a big difference in the digestibility. If you can wait, you probably won't experience the drop in milk production that many producers do when they switch from last year's corn silage to material that's only three weeks to a month old.”

Ruminal starch digestibility can increase by up to 25% during those first months, says David Weakley, director of dairy forage research for Land O'Lakes Purina Feed.

“Understanding the value that ample storage time has on corn silage is very important,” says Weakley, based in Gray Summit,MO. “It's a bigger variable in dairy rations because higher-corn-silage feeding programs are more prevalent than they used to be.”

If it's practical, keep a supply of last year's corn silage to feed while the current crop is gaining digestibility, the nutritionists suggest.

“Some growers use bunker silos and also put several weeks worth of silage in bags so they can keep some aside to feed right after harvest,” says Hutjens. “Others find it relatively easy to do if they use bunkers that can be accessed from both ends.”

Two final notes: 1) kernel processing aids quality improvement during those first few months because it exposes more of the starch to microbial attack, and 2) silage quality remains stable for two to three years in storage.