by Deborah Jeanne Sergeant
Managing harvest well can result in better quality and higher quantity of forage. Joe Lawrence, dairy forage systems specialist at Cornell University PRO-DAIRY, presented “Improving Harvest Management” as part of the 2021 Western New York Virtual Forage Congress.
“Harvest quality and silo management have profound effects on silage quality at feeding,” he said.
Poor quality forage, followed by poor silage management, results in the poorest quality of silage. As each of these two steps improves to high quality, livestock can enjoy excellent quality silage. “This highlights how we have to be good on both sides of the equation,” Lawrence said. “We have to grow a high quality forage and have good management.”
Whole plant dry matter affects quality. His research has looked at corn silage kernel processing and starch availability versus digestibility, which allows cows to utilize starch within the kernel.
“When we get corn silage forage analysis back, we see two main numbers related to quality/availability and digestibility,” Lawrence said. “There’s a lot of work ongoing in this area.” Research looks at what is digestible in the rumen and what is digestible in the total digestive tract of the animal.
“What it really comes down to when we process the kernel is it’s less about digestibility,” Lawrence said. “That has to do with biology in the animal and the type of corn and stage of corn. Kernel processing is about availability. If it’s still encapsulated in a kernel and passes through, it doesn’t matter the digestibility because it’s not available.” He added that kernel processing helps break down the kernel so it is available. This is measured by the kernel processing score (KPS).
“What would pass through a four millimeter sieve?” Lawrence asked. That can indicate what would be available to a cow.
“A change from poor to adequate is worth two pounds of milk or two pounds of corn,” Lawrence said.
He also presented 2018-19 research on corn harvester performance and hybrid characteristics. Hybrid selections were related to differences in plant size, relative maturity and kernel type.
“This study looked at the type of hybrid and how it affected processing and if there is a point of diminishing return when trying to get higher KPS,” Lawrence said.
Dairy One’s recommendation of greater than 70% availability is considered optimum; 50% to 70% is adequate; and less than 50% is inadequate. But Lawrence questioned exceeding the upper threshold.
“Should we be happy getting to 70%?” he asked. “How much money do we want to invest in equipment to get above that score?”
The factors are the ear to stover ratio (how much the ear weighs compared with the rest of the plant), relative maturity and how dry it is at harvest.
Lawrence noted that kernel type was not as effective. “What we were shooting for is much more plant material in reference to the ear,” he said. “These were all planted on the same day on the same farm. We also harvested on the same day and drove the same miles per hour while harvesting.”
Research revealed that each 0.1 unit in ear to stover ratio resulted in a 1.7% increase in corn silage processing score.
“Ear dry matter has implications as the season changes. If we start harvest and silage is a little on the wet side, we may get good processing scores, but in a few weeks, we may get one that’s drier. We can see a notable difference in processing score if we’re not making any adjustments,” Lawrence said.
Starch content also matters. “Leafy varieties get a bad rap for lower starch content,” he said, “but that means they have a smaller ear – or is the starch there diluted out by more stover?” He doesn’t think this is true in a lot of cases.
“Consistently in a lot of studies, ensiling time helps with starch digestibility,” he said. “One of the best things we can do to improve the digestibility of corn silage is increasing its fermentation time.” He recommended more than 135 days of fermentation to “close the gap” in digestibility.
“There’s been some suggestions that the kernel processing score went up during fermentation,” Lawrence said. “This is starting to give producers the idea that perhaps they didn’t have to be quite as vigilant at harvest for KPS. However, we did not find that.”
He and other researchers have theories about it but did not see any consistent increase in processing scores. Some of this could have been sampling variability.
“Do the best job you can to get into the mid to high sixties at harvest,” Lawrence said. “Don’t think you can consistently rely on fermentation.”
Growers often use growing degree days; however, Lawrence said that GDDs are not the same in how they affect whole plant dry matter.
“Ear plant dry matter contributes more to whole plant dry matter than stover, but that varies year by year,” Lawrence explained. “Ear dry matter can have a fairly big impact on KPS.” He encouraged growers to look at ears, not stover appearance. In 2018, warm weather provided good conditions for dry down, unlike the cool weather in 2019 which challenged growers.
“Keep an eye on whole plant dry matter,” Lawrence said. “Test whole samples, not the windshield test of plant color.”