Corn Silage

Corn silage is an excellent source of energy and fiber for dairy and beef cows. However, growing, harvesting, and storing corn silage has a significant impact on the overall quantity and quality of the silage.

Types of Silage Corn

Dual-purpose products

  • Have more flexibility for end use as either grain production or high tonnage/high energy silage
  • Tend to have wider adaptability because of the positive response to stress factors

Brown midrib (BMR) products

  • Are natural occurring mutants that have reduced lignin within the plant and may have the biggest impact on milk production for transition, early, and top producing lactating cows.
  • Tend to have lower yield potential (dry matter), less adaptability to stress environments, and lower disease tolerance. Starch content tends to be lower with BRM products.1

Leafy and floury-leafy products

  • Leafy products have more leaves above the ear that may increase digestibility and may have lower starch than dual-purpose products; however, the softer kernel is easily broken down during harvest and is more readily available in less time during the fermentation process
  • Takes less time to reach optimum levels in the silo, it can be an effective bridge between silage production cycles

Important Variables in Dairy Quality Silage

While there are well over 30 different variables that are and can be quantified with a laboratory analysis of silage; dry matter (DM), neutral detergent fiber (NDF), in vitro neutral detergent fiber digestibility (IVNDFD), and starch are the essential measures for evaluating corn silage quality. The single most important aspect in harvesting silage is the moisture level of the plant. If it is too dry, the silage will not pack well enough to allow for proper anaerobic fermentation. If it is to wet, the product may undergo excessive fermentation, reducing pH and increasing acetic acid. This could result in less intake of the product. High seepage loss associated with this situation, will reduce nutrient value and may cause environmental concerns.

Dry Matter is:

  • determined by the moisture level and is expressed as a percentage and has a target value of 30 to 38%.
  • highly correlated with plant maturity. As the plant matures, fiber digestibility will decrease, but starch content will increase.
  • silage that will be stored in a bunker or a bag can be chopped at a lower DM content, 30 to 35% as compared to upright silage storage at 35 to 40%.

Neutral Detergent Fiber is:

  • the fiber content of silage and is expressed as a percentage, with a target value of 35 to 55%. It consists of parts of the plant that are the less digestible components of the plant, such as cellulose and lignin. Generally, speaking the lower the grain content in the silage, the higher the NDF percentage. Corn that was severely stressed or immature will also result in a higher NDF percentage.
  • broken down by the bacteria in the rumen and often is an inverse predictor of intake, the higher the value, the lower the animal intake. Dietary fiber is an important factor in the ruminant rations and approximately 25% of the economic value of silage is as fiber source. If the NDF is too low, another fiber source must be added to the ration, often at a higher cost.

In Vitro Neutral Detergent Fiber Digestibility is:

  • a measure of potential digestion of the NDF portion of the silage and is very important in measuring silage quality. This is an in vitro measurement, incubated in rumen fluid for 24, 30, or 48 hours. The digestibility of any forage NDF incubated for 24, 30 or 48 hours are highly correlated. Therefore, any incubation time used ranks forage NDF digestibility in relatively the same manner.
  • dependent on laboratory conducting the analysis. Values less than the laboratory mean (and most labs will give you this number) should be fed in lesser amounts. Values higher than the laboratory mean are related with higher intake and consequently, more milk. Greater than the mean IVNDFD can be fed at higher rates and should be fed to early lactation cows.
  • impacted by maturity at harvest, product genetics, growing conditions, and management tactics. Generally, extremes in the range in percentage IVNDFD for dual-purpose corn products silage is be relatively small.

Starch is:

  • a energy component in corn silage and expressed as a percentage with a target range of 25 to 35%. If the content is below 25% the corn was stressed or processed to early.
  • negatively correlated with NDF, meaning when one goes up, the other goes down. Silage with high starch will have lower NDF and if fiber is limited, this could increase cost as those replacement fiber source may have to be purchased. On the other hand, as starch concentration increases, the energy value of the silage also usually increases and will reduce the amount of supplemental corn grain required.

Product Choice

The relative maturity of a corn product that is being planned for silage, is usually about 5 to10 units higher than one that is being used for grain. Other agronomic factors like tillage system, soil type and susceptibility to plant disease should also be considered. Placement and in season management for a product being grown for silage would be the same as if that product was being grown for grain. A consideration should be made for insect management, particularly the corn rootworm complex. Because the product being grown for silage may have a longer relative maturity, corn rootworm beetles in the late summer can be attracted to it as a later maturity product will be flowering later. Thus, corn rootworm larval populations in these fields can be significantly higher than corn with an earlier relative maturity the following year. Some brown mid-rib products have a lower tolerance to fungal diseases of corn and may require an application of fungicide to prevent losses, which should be considered when choosing a product.

Row Spacing

Corn planted in narrow rows (15 inches) as compared to (30 inches) yielded about a ton more per acre, but IVNDFD was slightly lower and NDF had a slight increase with increasing populations.2 The twin row planting does increase silage yield over conventional 30 inch rows, but other quality parameters are not influenced.3


  • Moisture: The single most important factor for obtaining high quality corn silage is harvest moisture. Depending on storage method corn silage should be harvested at a minimum of 30% to a maximum of 38% dry matter. If it is harvested above 40% dry matter the crop will be overly mature and it will difficult to pack and not maintain an aerobic environment required. Harvesting a higher percentage of dry matter will result in higher percentage of lignin, thus reducing the fiber digestibility. Since harvesting at the correct dry matter percentage is so critical, it is recommended that harvest begin at 30% dry matter to account for delays.
  • Height: Increasing the height at which the plant is chopped can increase NDFD and starch content in the silage. Research from Pennsylvania found when increasing the cutting height from 7 inches to 19 inches about a 7% increase was found in NDFD and about 6% increase in starch. However, by leaving the additional 12 inches of lower internodes, the dry matter loss was about 7%. A higher cut will allow less corn grain in the diet, allow for earlier harvest, and reduce nitrites when corn is under severe drought stress. High chop silage would be utilized best when fed to lactating cows, but storage maybe an issue as it would need to be stored separately. It is important to realize that increasing the cutting height will result in less overall yield. Thus, the increase costs of planting more acres to make up for the reduced yield, may not be economical in the long run
  • Kernel Processing: Whole plant (kernel) processing as the plant is being harvested accomplishes two functions, it sets the chop length and breaks the kernel to a degree that allows the cow to more efficiently utilize the starch component in the grain.5 Recommended setting for chop length if using a processor is ¾ of inch for dual purpose products. The use of the Penn State Separator to determine the chop length and adjust during harvesting is recommended.6 This tool will help both packing of the silage in storage and rumination in the cow. The kernel should be processed such that a kernel processing score of over 50% is achieved; however, a score of 70% is optimum.
Figure 1. Influence of plant population on silage yield. From Cusicanqui, J. A. and Lauer, J. 1999. Plant density and hybrid influence on corn forage yield and quality. Agronomy. Journal . 91:911-915.

Plant Population

In most cases, corn that is being grown for silage is planted at 10 to 20% higher than would be planted for grain. Generally, as population increases, yield per acre increases; however, there may be a decrease in quality. As population increases, NDF concentration increases resulting in a decrease in digestibility. In studies conducted in Wisconsin forage yield was highest at 44,000 plants/acre; however, silage quality was highest at 20,000 plants/acre. The balance range was between 38,000 and 41,000 plants per acre (Figure 1 and 2). In research conducted in New York, IVNDFD had a 0.1% decrease and NDF had a 0.13% increase per 1000 plant/acre increase.7

Figure 2. Influence of plant population on silage quality. From Cusicanqui, J. A. and J. G. Lauer. 1999. Plant density and hybrid influence on corn forage yield and quality. Agronomy. Journal 91:911-915.