Whole-plant corn harvested as silage provides a major portion of the forage inventory on many dairy farms.

Corn silage is normally a high-energy forage crop with high per-acre dry-matter yield potential relative to other forage crops, according to J.W. Schroeder, North Dakota State University Extension Service dairy specialist.

“The nutritive value of whole-plant corn harvested varies with its proportion of grain, fiber content and digestibility, starch content and digestibility, oil content and protein content,” he says. “The type of corn hybrid selected for production of whole-plant corn harvested affects these characteristics.”

Most of these characteristics also are influenced greatly by other factors, such as harvesting at the correct time and processing the corn properly. Here are Schroeder’s answers to producers’ questions:

Q: At what stage of maturity should we harvest?

A: Years ago, experts recommended that corn silage should be harvested at the black-layer stage of maturity. In recent years, research and field experience has shown that this practice usually results in silage that is too dry to be well-utilized by dairy cows. Positioning of the kernel milk line also has been used as an indicator of when to harvest whole-plant corn for silage. The best lactation performance by dairy cows has been shown to occur at roughly the one-half milk line stage of maturity.

But recent research and field experience has shown considerable variation in the relationship between whole-plant moisture content and positioning of the kernel milk line. This variation is related to differences in hybrids and their dry-down characteristics and differences in growing conditions. Blindly harvesting whole-plant corn for silage at the one-half milk line sometimes will result in silage without the right moisture content.

Q: At what moisture should we harvest?

A: The best lactation performance by dairy cows has been shown to occur at 65 percent to 70 percent whole-plant moisture. This range in whole-plant moisture content works well for achieving good preservation in horizontal silos. Harvesting whole-plant corn with more than 70 percent moisture increases seepage losses; increases acidity, which can lower dry-matter intake; and reduces dry-matter yield per acre.

Whole-plant corn harvested for storage in upright silos may need to be chopped a bit drier than 65 percent moisture to minimize seepage. But research consistently has shown reduced fiber and starch digestion, along with reduced lactation performance, for corn silage harvested at 60 percent moisture or less. Corn silage harvested at 60 percent moisture or less either will need to be chopped fine or processed to minimize losses in starch digestion and lactation performance.

Q: At what length should we chop?

A: The general recommendation for corn silage harvested with a conventional harvester (without a crop processor) is three-eighths inch theoretical length of cut (TLC). This recommendation may vary between one-quarter and one-half inch TLC, depending upon whole-plant and kernel moisture content, hybrid and forage harvester. To get good breakage of cobs and kernels with a conventional harvester, you often must chop finer than you would like from an effective fiber standpoint. Unbroken kernels tend to pass through the cow undigested and large pieces of cobs or whole cobs are prone to sorting in the feed bunk. This typically means that only 5 percent to 10 percent of the silage should be in the coarse particle fraction or retained on the top screen of the Penn State-Nasco shaker box.

Q: How do we process the corn?

A: Based on Wisconsin research, the recommended roll clearance ranges from one-sixteenth to one-eighth inch (1 to 3 millimeters). Roll clearance is determined using feeler gauges. If you do not have feeler gauges, lay the blade of your pocketknife flat between the rolls and adjust the clearance until the rolls tighten against the blade. Harvest some whole plants, shake out the chopped material and visually inspect each screen for the degree of kernel and cob processing.

We would like to see all of the kernels broken. Pieces of cob, if discernible, should be no larger than the end of your little finger. If kernel and cob breakage is not complete, then tighten the rolls until kernel damage is complete or consider reducing your TLC. With processed corn silage harvested at an immature or wet stage that tends to mush, you can set roll clearance to one-eighth inch (3 millimeters). Make sure you follow all recommended safety practices whenever making any machine adjustments.

Q: At what height should we chop?

A: Silage dry-matter yield is reduced about 15 percent as the row-crop head is raised from 6 to 18 inches. But estimated milk per ton increases because the more fibrous and less digestible portion of the whole-plant material is left in the field. This results in estimated milk per acre being reduced only about 3 percent.

Prioritize your needs for maximum yield versus high quality to determine the best cutting height for your situation. This may vary from year to year, depending upon the inventory and quality of your hay crop silage. Also, because nitrates tend to concentrate in the bottom portion of the stalk, raising the crop head helps minimize nitrate if that is a concern.

“Harvesting whole-plant corn at the right moisture content and particle size is crucial to making high-quality corn silage that is well-utilized by dairy cows,” Schroeder says. “Whole-plant moisture content, rather than kernel milk line positioning, should be your trigger for when to harvest corn silage. Monitor particle size and kernel and cob breakage to ensure that the forage harvester-crop processor is doing the job. Remember to use additives properly, pack well and cover securely to minimize storage losses.”

For more information on making corn silage, visit http://www.ag.ndsu.edu/pubs/ansci/dairy/as1253w.htm.

NDSU Agriculture Communication