Corn Silage – Making it Work for You

When made properly, corn silage can be one of the greatest energy feeds for dairy cows. However, the ability to put up good quality corn silage seems to be more of an “art” than a “science”. Depending on your geography, there are many aspects that need to be considered when managing corn silage.

Moisture and Maturity

The most important factors in determining when to harvest corn silage are maturity and moisture. Proper maturity aids in assuring adequate fermentable sugars and starches for silage fermentation bacteria to maximize forage nutritional value. Historically, it was recommended to determine corn maturity by following the kernel milkline. The milkline represents the accumulation of starch content within the grain kernel. As the plant matures and the kernel hardens, the milkline moves towards the cob. Harvesting between 1/3 and 2/3 kernel milkline has been used as a rule of thumb to produce optimal results in animal performance. However, newer hybrid varieties with different plant dry down rates than conventional species reduce the efficacy of relying on the milkline alone to best determine when to harvest corn for silage.

Ensuring the proper plant moisture content must also be considered in determining when to harvest corn silage. Maturity has a significant influence on moisture content of unwilted forage crops such as corn silage. The adequate time for harvesting corn silage is when the moisture content of the entire plant reaches 65% to 70% (or 30% to 35% DM). Chopping forage at the correct moisture is essential for adequate anaerobic fermentation conditions and packing. Harvesting corn silage at high moisture content (75% moisture or more) causes substantial storage losses, seepage, and improper fermentation, laying the foundation for undesired mold and toxin production. However, harvesting corn silage too dry (60% moisture or less) impedes packing capability, hinders the ability to limit oxygen, and elevates the probability for undesirable fermentation products, resulting in reduced starch digestibility. In order to determine the current moisture content of standing corn plants, select 10 to 12 plants from throughout the field. Using a wood chipper, chop the entire plant and gather a subsample of 100g to determine the dry matter. Using this determined plant dry matter in conjunction with the total corn plant daily dry down rule of thumb of 0.5 percent units, one can best decide the proper time to harvest corn silage.

Height and Length of Cut

In order to maximize yield per acre, silage digestibility, and minimize soil contamination, corn silage should be harvested at 6″ to 8″ above the ground. The exception to this range occurs when harvesting stressed crops. Corn stressed by drought or heat has the potential to accumulate higher levels of nitrates in the lower portion of the plant stock. Nitrates are the main precursor for plant proteins. Under stressed conditions, the plant loses its ability to metabolize the nitrates, causing them to build up. Toxic levels of nitrates are responsible for the creation of lethal silo gas (nitrogen dioxide) as well as interfering with the ability of blood to carry oxygen. In drought stress conditions, one should wait 7 days after rainfall to harvest in order to help minimize the impact of potential nitrate toxicity. An alternative method is to increase the stubble cut height to 12″ to 16″ above the ground.

When chopping corn silage, it is important to consider the configuration and sharpness of the harvester knives to ensure a proper theoretical cut length (TCL).The most desired TCL falls between 1/4″ to 3/4″, depending on the hybrid, storage structure, and amount of silage inclusion in the ration. Aiming for a TCL of 1/2″ (12mm to 17 mm) helps ensure adequate particle length for both silage packing and effective fiber. If the TCL is too long, the ability for proper silage compaction and oxygen exclusion is impeded. Additionally, if the TCL is too short, animal performance may be negatively affected by lower milk fat production and/or higher incidence of displaced abomasum’s due to inadequate levels of effective fiber (scratch factor).

Filling, Packing, and Storing

When making any silage, the crop should be harvested, ensiled, packed, and covered as quickly as possible to prevent excessive plant respiration and dry matter loss. Infiltration of air and moisture increases the potential for poor fermentation and spoilage, lowering the silage nutritional value. Spoiled silage will also be avoided by cows, lowering their intake. Dairy cow dry matter intake is directly correlated to milk production. If cows sense spoiled silage, intakes will decrease which will in turn, lower milk yield.

In bunker type storage systems, adequate compaction is essential to remove as much oxygen as possible to ensure anaerobic conditions. When filling a bunker, it is best to spread the forage in thin layers (< 6inches) on the sloped filling face (wedge shape). Driving over each layer multiple times with a heavy tractor will remove air and ensure proper packing. Additionally, using the wedge technique covers previous layers of forage, reducing air exposure and plant respiration.

Regardless of the forage storage type, the silage should be sealed air-tight with low oxygen permeable plastic or weather-resistant plastic for a minimum of 21 days. This will allow adequate time for fermentation to occur, stabilize, and increase the nutritional value of the forage. Feeding the silage before it has had adequate time to ferment increases the probability for secondary fermentation, decreased nutritive value and daily quality variability, negatively impacting animal performance. Ideally, it is best to allow 3 to 6 months of fermentation to occur in order to optimize starch digestibility.


Kernel processors are a helpful tool when managing corn silage. Corn silage processing is marketed on the ability to reduce the percentage of undamaged corn kernels and achieve greater effective fiber values. Kernel processors are not to be confused with recutter screens. These attachments recut the entire plant into smaller pieces, reducing the TCL and forage effective fiber thus predisposing the cows to digestive upsets. Processing of corn silage has substantial effects on silage quality. With lack of control over weather and climate, corn can over mature, creating hard kernels with reduced digestibility (intact kernels will pass through the cow and show in the manure). Counter-rotating rollers within kernel processors damage the kernel, allowing silage fermentation bacteria access to a greater concentration of starch and sugar, improving the fermentation process. Similarly, the rumen microbe’s will have improved access to kernel starch, increasing the rate of whole crop dry matter digestibility in the rumen by 3%, total tract digestibility by an average of 1%, and NEL energy content by 0.5 to 4%. This in turn leads to an average of 0.5kg more milk per day, as well as 0.10% units in milk butter fat percent. Another benefit is reduced cob waste. Reducing feed bunk cob waste encourages the herd to eat the ration delivered to them, improving ration consistency and digestibility. However, processors will reduce TCL by 15-30%. Therefore, processed corn silage should be harvested at an increased TCL (1/2″ to 3/4″). This enables the ability to maximize effective fiber sources without affecting starch digestibility or rumen health.


Lastly, Inoculants can provide added protection to aid in the preservation of silage. Knowing what type of inoculant to use will help as these products are not a one size fits all. Homofermenters (Lactobacillus bacterium) only produce lactic acid. These kinds of bacteria speed up the fermentation process by dropping the forage pH faster, increasing lactic acid production, and maximizing sugar values of the forage. Heterofermenters (buchneri bacterium) produce both lactic acid and other products like acetic acid. These kinds of bacteria help to extend the shelf life of silage during feed out. Both inoculant types provide decent performance in livestock, with homofermenters having a slight edge with 3-5% of improved animal performance. Which inoculant is used depends on the forage conditions prior to ensiling. However, inoculants will not provide any benefit if other areas of silage management are not executed properly.

When creating corn silage for dairy operations, maximizing forage quality is crucial to optimizing animal performance and production. Paying attention to details may be the deciding factor between good quality and sub-par quality corn silage for the entire crop year. Work closely with both your agronomist and nutritionist to aid in creating and managing good quality forage for your operation.