Chop Length and Kernel Processing Raise Corn Silage Value
By Dr. Bill Seglar, veterinarian/nutrition specialist, DuPont Pioneer
Chop length and kernel processing are absolutely essential for corn silage. Kernel processing impacts the degree of starch digestion, while setting the theoretical length of chop (TLC) impacts particle length needed for proper rumination. While planning for harvest, go through a checklist for the silage harvester to ensure you will obtain well-processed silage.
Making Sure the Forage Harvester is Ready
Ensuring good kernel processing starts several weeks prior to harvest. Make sure the entire chopper is in good condition, especially the chopper knives and the roller mill. Nicked knives and worn shear bars should be replaced to prevent uneven and shaggy chop lengths. The entire length of the roller mill should be checked for wear on the teeth. Uneven wear may prevent narrowing of the roller gap: Hours of operation may allow the outer edges of the rollers may touch, leaving an undesirable gap in the middle.
Replace the rollers if they show signs of wear (retooling services are available from some machine shops). Inspect the roller mill after 400 hours of use. The integrity of the working parts and hours of effective use depend on soil type and other environmental factors. Corn grown on sandy soil, where wind is common, results in more wear and tear, shortening roller mill life. Other factors include roller size and the number of teeth per inch. More aggressive differential speed options will affect the life of the roller mill.
After inspecting the chopper head and roller mill, check the gap setting between the rollers. It should be 1 to 2 mm to ensure it cracks all the kernels. Check using a dime (1.2 mm wide): If there is excess space between the rolls and the dime, tighten the gap. Next, set the TLC at 3/4 inch, which is longer than the typical 3/8 to 1/2 TLC settings for non-processed corn silage.
The feed roll speed determines TLC: Slowing down feed rolls produces a shorter chop length because less forage is pushed through the chopper drum at one time. This results in fewer tons/hour chopper capacity, requiring longer time to chop and adequately process the crop. However, the extra time you take pays off during feedout because you’ll have well-processed, high-quality corn silage that improves milk production and profitability.
Variables Impacting Processing of Corn Silage
All brands of harvesters (with processors) in good working condition can achieve well-processed corn silage, provided users pay attention to the nature of the crop. The grain-to-stover ratio of the crop impacts how much grain goes through the roller mill. The higher the grain content, the greater the need for more aggressive processing. Sometimes that means shortening the TLC to achieve better kernel processing of high starch corn silage.
Harvest moisture also impacts kernel processing. The lower the moisture, the higher the starch content. As you harvest dryer corn, you can decrease the TLC setting. This may lower effective fiber, but it will ensure adequate packing of the dryer forage in the silo.
If feed roll and roller mill adjustments are not producing expected kernel processing results, inspect the differential speed of the roller mill. The upper roller should run faster than the lower roller. Differences of 10 percent to 15 percent are common.
If processing is not meeting your expectations, try installing a smaller sprocket on the upper roll. This results in differential speeds in excess of 20 percent. Some manufacturers have engineered roller mills to accommodate a 30 percent to 50 percent speed differential. Of course, with all these guidelines, it is always best to refer to the manufacturer’s guidelines for specific setting adjustment information.
Monitors of Processed Corn Silage
Several forage testing laboratories offer a scientifically validated sieving test known as the Ro-Tap system for quantifying corn silage processing. The procedure produces the Corn Silage Processing Score (CSPS) values based on percent of starch passing through a 4.75 mm sieve, which represents a percentage of total starch in the sample. Here are CSPS interpretation guidelines for the Ro-Tap system used to measure degree of kernel damage in corn silage:
- Less than 50 percent = inadequate
- 50 percent to 70 percent = normal
- 70 percent = optimum
Dairyland Laboratories, Inc., summarized CSPS values for 2009-2014 samples and broke the findings out by low, average and high starch levels. Lower-starch corn silage has higher percentage of inadequate CSPS values. Higher starch concentrations show a lower percentage of inadequate CSPS values.
These differences in CSPS value likely exist because, as maturity advances with declining moisture levels, starch deposition increases. That results in a dryer kernel that the roller mill will better fracture into small particles. Another consideration: At higher moisture levels, with less starch and more stover, a higher percentage of kernels may be protected from damage by the stover, resulting in less-than-ideal kernel processing. Also, as farmers and custom chopper operators harvest less-mature corn silage, they may not be as concerned about ideal processing and will open up the roller mill for a less aggressive KPS.
Although many producers are meeting KPS goals, there is room for improvement on roller mill settings to achieve optimal kernel processing.
While the CSPS is an excellent test, the hectic corn silage harvest season doesn’t permit timely CSPS determinations to make sure the harvested crop has proper KPS and TLC values. We need a field monitoring system for use during harvest to determine the degree of kernel processing. Growers can inspect loads coming to the storage structure for kernel damage. They can notify the chopper operator if adjustments are required to improve processing.
Processing effectiveness may change from field to field and from day to day, so it is important to monitor kernel processing throughout the entire harvest. Samples should be checked at least once daily and whenever the chopper operator switches to a different field. In some cases, producers need to inspect every load coming to the silo.
The Corn Silage Processing Monitoring Cup is a quick, simple on-farm technique to check degree of processing. DuPont Pioneer forage experts around the world use this method. It involves collecting a 1-liter (32 oz.) cup of chopped forage for field analysis.
Spread the collected sample on clean ground and manually sift through the sample, counting all kernels larger than half a kernel. Kernels need to be completely fractured, not just nicked. The guideline is no more than two whole or half kernels per sample. While dairy operations and chopper operators may agree on another threshold, the count should never exceed four half-to-whole kernels.
The monitoring cup wasn’t developed to quantify the degree of kernel processing as accurately as the laboratory Ro-Tap system. However, it can help silage managers adopt a more aggressive CSPS.
Most dairy operations pay a great deal of attention to business management decisions that aim to produce milk in the most efficient manner at the highest level of profitability. Achieving well-processed, high-starch corn silage is a key to higher-quality corn silage. Operations can reduce levels of supplemental grain in the ration and save costs on rations. It makes good business sense to inspect the kernel processer and chopper settings before harvesting to help ensure their corn silage will help them achieve maximum milk production.