“And no one, after drinking old wine, desires new, for he says, ‘The old is good.’”
As it turns out, this age-old wisdom from the Bible applies not just to wine, but to corn silage, too.
Michelle Chang-Der Bedrosian, PhD, Forage Technical Specialist with Vita Plus, shared her own wisdom with attendees of the World Forage Analysis Superbowl seminar series at the 2021 World Dairy Expo in Madison, Wis. Her presentation, “Forage Storage: Life After Harvest” dove deep into the science of why feeding properly aged corn silage is essential for optimal nutrient availability, milk production, and rumen health.
“There was a time when we thought that once a silage crop was packed and sealed, that was it,” she shared. “We thought we basically put the lid on it, it stayed stagnant, and it was ready to go whenever we needed it.”
But researchers have since learned the microbial processes that take place after corn silage is put to bed is actually when the real magic happens. Over time, the anaerobic environment created in a well-packed, well-sealed, inoculated silage crop allows the beauty of fermentation to flourish.
Chang-Der Bedrosian is a microbiologist by training and also serves as an adjunct professor at the University of Wisconsin-Madison. She said the main accomplishment of fermentation – and what really turns corn silage into “jet fuel” for cows – is starch digestion. “Fiber digestion will remain fairly steady during storage. So whatever level of fiber digestibility you put in the bunker or bag as a result of hybrid choices, harvest conditions, etc., is pretty much what you’ll get back out,” she stated.
Starch digestibility, on the other hand, gets better and better the longer a crop ferments. This happens because lactic acid in the crop increases over time, while the pH drops. As lactic acid bacteria grow in the silage, they produce proteolytic enzymes that gradually break down prolamin proteins, which are like a waterproof mesh that encapsulate the starch particles in corn kernels.
The true “magic” of fermentation bacteria is that they break starch into usable fractions that are exactly what dairy cows need to make milk – specifically, propionate in the rumen, and glucose in the liver. Amazingly, digested starch actually yields about 10% more energy than if the cow directly consumed glucose.
Kernel processing at harvest is one way to promote starch digestibility. Chang-Der Bedrosian advised that every corn kernel should be broken into at least four pieces before it is ensiled. But, she said, even the laudable efforts to process kernels are trumped by prolonged storage, which can break starch particles down into exponentially smaller fragments than kernel processing alone.
“Length of storage is mathematically more important than kernel processing,” she declared.
She also shared an illustration of why switching abruptly from old-crop to new-crop corn silage is a recipe for disaster in terms of milk production and, potentially, cow health. “At the end of a feeding year, we likely are serving up excellently fermented corn silage, with starch digestibility as high as 85% of available starch,” she explained.
“If we switch overnight to a new batch with just 70% digestibility, milk production will understandably tank. Suddenly, the rumens, whose microbial populations were well-adapted to high levels of starch, are suddenly shocked by a feedstuff they cannot process well.”
Her solution: plan ahead to build an inventory of at least three months’ worth of corn silage beyond harvest, so the new crop can ferment at least 90 days before feed-out starts.
That may be a tricky proposition, based on each dairy’s crop availability and pad and bunker space. But Chang-Der Bedrosian said she has seen many creative feeding scenarios that producers have used to make it work. Some feed out of opposite ends of the bunker, or split their bunkers lengthwise with a concrete wall. Others store their carryover “stash” separately in its own bag or drive-over pile.
“The key is to make sure the strategy minimizes face exposure, so we don’t compromise the quality of a carefully ensiled crop,” she emphasized.
If such a carryover inventory isn’t possible, Chang-Der Bedrosian said additive protease products have been proven to accelerate starch digestibility so the crop can be fed sooner. “But it’s possible to avoid incurring that additional cost,” she noted. “We can achieve the same result by strategizing, planning ahead, and simply providing enough time to allow fermentation to work its wonders.”
