Why we process corn silage

As corn silage makes up more and more of dairy diets, it's easy to forget that the corn grain in that silage has become the engine that powers milk production.

Gone are the days when 25 or 30 lb. of corn grain is added to the TMR. Now, grain in silage drives cows' ability to milk.

It's all economics. "If you're not two-thirds or even three-quarters corn silage, don't talk about feed costs," says Mike Hutjens, a University of Illinois Extension dairy nutritionist. Regardless of the ingredient cost software you use, corn silage is always the cheaper source of nutrients, he says.

Milk per ton of forage is more often than not better with corn silage (conventional or BMR) than alfalfa hay or haylage. And that's even when you compare the best to the best.

At the 2015 World Forage Analysis Superbowl, conventional and BMR corn silage had a 15 to 18% advantage over the best alfalfa in terms of milk per ton. Alfalfa haylage did a bit better than commercial dairy hay, but corn silage still out-performed both. And when you add on the higher tonnage per acre corn produces, corn silage has even more of an advantage.

Ease of growing and harvesting is another check in corn silage's favor. But that's not to say corn silage is a growit, chop-it and forget-it kind of crop. Far from it. Hybrid selection, agronomics and harvest management are now paramount.

Recent data from feed testing labs shows farmers are getting better at managing corn silage harvesting. Of the 1,000-plus corn silage samples evaluated from the 2015 crop by Dairyland Laboratories in Arcadia, Wis., 23% were processed at optimal levels.

That's up from 20% of samples over the past five years. Still, more than 60% of samples have only been adequately processed and are giving up two pounds of milk per cow per day. About one out of seven are poorly processed, giving up 4 lb./cow/day, says Hutjens.

More Corn Silage, Less Fiber

As farmers have increased corn silage in their milking cow diets, having enough effective fiber has become a concern. Finely chopped silage, to allow adequate packing density in storage and to prevent feed sorting at the bunk, means the material doesn't stay in the rumen long. Having enough effective fiber to create an adequate rumen mat is key for proper ruminal digestion.

Enter shredding processor units that allow for a longer length of cut but rip and tear corn plant fibers in hopes of providing more effective fiber and more digestibility of neutral detergent fiber (NDF).

Both are important, says Jim Barmore, with GPS Dairy Consulting, based in Verona, Wis. But he and Hutjens agree the shredder processor units now available from the major chopper manufacturers are simply better at ripping and mashing up corn grain than older units that were designed just to process corn kernels.

The GPS consulting group includes 12 dairy nutritionists and veterinarians. Collectively, the group feeds more than 150,000 cows across 10 states in the Midwest and internationally. These cows consume one and a half million tons of corn silage each year, the majority of which is now being processed with shredder units.

"Kernel processing is the #1 reason we process corn silage, because the grain is the biggest contributor to ration energy," he says. Starch availability is the key to corn silage performance.

"Grain particle size matters, and it matters a lot," Barmore says. "We've proven that with dry corn, high moisture corn and fecal manure scores."

Chop length also comes into play because of the need for effective fiber. When shredder units first came out three and four years ago, the preferred length of cut was 28 to 30 millimeters (mm) or 1.1 to 1.2". "But we were

too challenged by sorting at the bunk with those lengths," says Barmore.

Now, he's settled in at 24 to 26 mm (.95 to 1.0"). "That's not fully proven, but it's the best number we've come up with based on our field experience and not have excessive sorting," he says. "In other words, we don't want particles any longer than the width of an American quarter dollar coin."

Processing also should enhance NDF digestibility. With proper processing, you no longer get those corn stalk particles that look like cigarette butts. Without processing, those don't get digested and are lost in manure. "With processing and effective shredding, I think you do see some improvement in more consistent fiber digestibility in the rumen," says Barmore.

Some argue that shredder-processed corn doesn't pack as well in the bunk. "We have real data that shows that's not true. The corn kernels are so much better processed that we think that may allow for better packing," he says.

But plant moisture plays a critical role here as well. Chopping at 33 to 34% dry matter is ideal. Once it reaches 36 to 37%, Barmore urges clients to decrease particle length to ensure adequate processing and packing density at the bunker.

Farmer Experiences

Brothers Mike and Tom Gerrits, Greenleaf, Wis. just south of Green Bay, have been using a shredder processor on one of their two choppers for three years. They milk 3,700 cows and farm 6,000 acres, half of which is corn silage.

They hope to add a shredder unit when they next trade-up choppers, but for now, they process silage for only 2 ¬Ω to 3 months' worth of feed. "With unprocessed silage, we're feeding 66 lb. of corn silage per cow per day. With the processed silage, we're able to bump that up to 82 lb.," says Mike.

"The hybrid we processed was more of a grain variety, and it was very high in starch at 44%," he says. (More typically, starch will run 35 to 38%.) "Cow performance has been great. We're typically over 100 lb./cow tank average. We've been able to maintain that with the processed silage, and we're up to 102 lb.," he says.

With shredder processing, the Gerrits hope to eventually eliminate straw from their milking cow diets. "I would love not to have to feed straw, because there's so much shrink processing and handling it," Mike says.

Paul Prohaska, who milks 1,400 cows with his wife, Kari, and brother Josh, near Marathon in northcentral Wisconsin, has been using a shredder processor for four years. He wouldn't go back.

"Our goal is to have no whole kernels, and the shredder processer is much better at kernel processing than the kernel processers were," he says. "We shoot for a Kernel Processing Score (KPS) of 70%+, and last year we were at 73% KPS."

Still, the Prohaska haven't adjusted their diets all that much. They feed about 50 lb. of corn silage as fed, or about 60% of the forage dry matter. Alfalfa makes up about 38% of the forage dry matter, and they're still adding 0.8 lb. of straw. The whole point of processing is to take full advantage of the corn grain in the silage, and with a 98 lb./cow/day tank average, Prohaska thinks they are.