10/22/2024
Field Monitoring of Kernel Processing in Corn Silage
Shared from Inside the ZONE® newsletter, Pioneer Nutritional Sciences
Corn kernels in silage must be fractured or processed or they will not be digested well by cattle. The Ro-Tap method is a laboratory procedure for estimating the degree of processing of kernels in chopped forage or corn silage. The simplified method outlined below can be used in the field for checking the degree of kernel processing of chopped forage. This system allows processing adjustments to be made immediately rather than waiting for lab results but still give values similar to the Ro-Tap method.
Sample
Collect a 32 oz. cup of chopped forage or silage for field analysis. If a 32 oz. cup is not available, a double-handful of silage is roughly equivalent. Select a freshly chopped sample that is representative of forage being harvested or a silage sample from storage. Response of forage to processing will differ with grain dry matter, whole plant dry matter, grain content, and genetics of the corn. Responses to kernel processing equipment also will differ with the roller gap, roller settings and wear, and the rate of harvest. Because processing effectiveness may change from field to field and from day to day, it is very important to monitor kernel processing throughout silage harvest. During harvest, samples should be checked at least once daily and whenever one switches from one field to the next.
Separate and Count the Kernels
Manually sift through the entire sample counting all kernels that are half or larger kernels. A nick is not enough. The kernels need to be completely fractured. Any kernel greater than half its original size should be included in the count.
Interpret the Results
The Ro-Tap® laboratory test measures the percentage of starch from a dried sample that will pass through a 4.75 mm screen and thereby is well digested. That Ro-Tap score can be estimated from the number of kernels found as shown in the figure below.
Kernel Processing: Field vs. Lab Test
1/2 or larger kernels / 32 oz cup (double handful)
Fermented composite samples from 33 Michigan silos, 2012 corn silage crop
CAUTION: The accuracy of this field test can vary with the ratio of grain to fodder within the forage or silage. Accuracy is best when starch content falls within the normal range (30-38%).
- ≤ 4 half or larger kernels (≥ 70% lab KP score)
- Starch energy availability is near the maximum point for ruminal fermentation and intestinal digestion. Few undigested corn kernel fractions will be found in manure.
- ≥ 5 half or larger kernels (< 70% lab KP score)
- A higher number of kernels matches with a lower processing score. The lower the KP score the more kernel fragments will be found in manure. These fragments contain starch that was NOT digested by the animal. Incomplete starch digestion reduces performance and increases feed costs because animals must consume more feed to compensate for incomplete digestion of the starch energy.
Adequate kernel processing is the simplest method to insure a high starch availability of corn silage. Other factors frequently associated with increased starch digestibility include a.) higher kernel moisture content at harvest and b.) longer time in storage. Rumen digestibility of starch increases during the first 2 to 3 months of fermentation.
Adjust Equipment to Increase Processing
The effectiveness of a kernel processor depends upon several factors. One or more of these factors should be changed to increase the kernel processing score.
- Narrow the roller gap.
- Increase the differential speeds between the rollers to increase tearing action.
- Replace worn rollers. As processor rollers wear, the aggressive nature of roller teeth may wane. Uneven wear may prevent narrowing of the roller gap because the outer edges of the rollers may touch even through a gap remains in the middle.
- Reduce forage harvester ground speed. High throughput will spread the rollers reducing the effective roller gap and can result in drive belt slippage that reduces the speed differential between rollers.
- Install rollers with a more aggressive design.
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