August 9, 2022
Data from research conducted last year by Allen Wilder, a forage agronomist with Miner Institute in Chazy, N.Y., shows that processing a floury corn silage hybrid increased starch digestibility and the soluble starch pool, despite resulting in a lower-than-desired kernel processing score of 70.
"A high-quality forage that is high in starch content is only good if the starch is available to your cows,” Wilder says. “The softness of the floury-type kernels may have allowed them to flatten without breaking apart in the processing in this trial. This research suggests that a different guideline may be needed in regard to optimal kernel processing of floury corn hybrids to create a better indicator of this starch availability for this type of hybrid."
Kernel processors work by crushing the forage between rollers as it passes through the harvester, and adjustments can be made to change the aggressiveness of the processing as needed.
Inadequate processing leads to lower starch availability and can result in lost milk production. Overly aggressive processing can lead to high fuel consumption, processor wear and only marginal nutritional benefits.
Recent corn silage processing research in New York by Cornell suggests that corn silage processing scores — a lab analysis for kernel processing — can lead to diminishing returns at high levels of kernel processing.
The study also showed that while starch digestibility was improved by kernel processing in fresh forage samples, starch content and starch digestibility were negatively affected in samples that were fermented for 135 days. This is cause for concern since the purpose of kernel processing is to improve the utilization of corn silage starch.
Optimally processed corn silage is considered to have a kernel processing score of 70 or higher, with adequately processed corn having a score greater than 50. It’s recommended that the kernel processor roller gap be set between 1 and 3 millimeters.
Last fall, two corn hybrids — both Brevant hybrids — were harvested with a self-propelled forage harvester equipped with a kernel processor. One was a vitreous kernel type, the other a floury kernel type. The kernels were in the half to three-quarters milk line stage of maturity.
During harvest, the kernel processor roller gap was adjusted to create two different processing levels: heavily processed at a 1.5-millimeter gap, and moderately processed at a 2.5-millimeter gap. Bucket mini-silos were filled with harvested material from each hybrid-processing level combination, and opened at 0, 45-, 90- and 135-day fermentation time points. The study had four replications.
Wilder also evaluated the effects of fermentation on starch availability in these two types of hybrids.
"Feedout of the floury hybrid, particularly in the initial stages of fermentation, may allow larger particles of starch to be fully digested in the cow rumen," he says.
Wilder’s data showed that fermenting at least 90 days is essential to maximize both the digestible and soluble starch pools in corn silage, regardless of the aggressiveness of kernel processing.
However, "while our maximum in vitro starch digestion plateaued by the 90-day point, actual starch digestion in the rumen may still benefit from additional fermentation time since the greatest soluble starch levels were not achieved until the 135-day point,” he says.
The degree of processing did not significantly affect the content of starch or sugar in this trial. But during fermentation, the heavily processed vitreous corn showed a consistent numerical decline in starch content as compared to the moderately processed vitreous corn.
“The hypothesis that this change in starch content was due to degradation into other pools [such as soluble starch or sugar] was not supported by the study results, and the fate of the lost starch remains unclear,” Wilder says.
This project was one of the first of its kind to use a soluble starch analysis developed by Cumberland Valley Analytical Services Inc. to quantify the starch that readily moves into suspension in an aqueous environment, like a cow’s rumen. Specific guidelines and animal performance benchmarks for this analysis are yet to be determined.
Wilder says there are opportunities for future research. "The value of soluble starch analysis as an indicator of cow performance is still unproven,” he says. “More data is needed to be able to develop guidelines for that fraction in addition to the kernel processing score.”
Dunn writes from her home in Mannsville, N.Y.
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