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Corn silage feeding guidelines for dairy production

Bill Seglar Published on 30 June 2014
corn harvest
top resource article

Q. Why is this a top resource article?

"I believe the reason for continual reference to the corn silage article is because every year corn silage growers and cattle/dairy producers need to review corn silage production goals with their respective teams. These teams include people harvesting the crop in the field, people filling the silos and finally people involved in feedout management and working to balance around transition from old to new crop corn silage. Once everyone on the team is aware of what is expected with the corn silage crop, then those beef and dairy end users have a better chance of feeding the highest quality silage to their cattle. As has been my goal with writing my articles for farm publications, I've always tried producing a list of basic action points for discussion along with providing recommended goals.” —Bill Seglar



Inclusion of corn silage into dairy rations is more complex than other feed ingredients because corn silage is really two feedstuffs: high-moisture corn grain and grass silage.

As a result, the nutritional value of corn silage can vary based on crop growing conditions, harvest moisture and the type of fermentation that occurred in the silo.

When growers transition from old-crop to new-crop silage, the potential for nutritional variability in feed value requires dairy producers to conduct laboratory analyses before making ration adjustments. Specifically, harvest moisture, starch content and neutral detergent fiber digestion (NDFD) differences between the old and new crop needs to be known.

Furthermore, testing for nutritional variations during the silo feedout process is essential to ensure rations maintain consistency in providing high-production dairy cattle with the nutrition intakes required for maximizing milk performance and rumen health. At the very least, constant monitoring for silage moisture changes during feedout is essential for ration changes to ensure consistent feeding of required nutrients from corn silage.

The first guideline for feeding corn silage is to determine its palatability to dairy cattle, which will affect acceptance and dry matter intake. Preservation quality determines palatability and is a reflection of harvest moisture, silo filling and silo unloading management factors.


Well-fermented silage should include no visible signs of spoilage. Silage surfaces that heat up during feedout and get even hotter in the ration at the feedbunk are indicators of spoilage microbial activity that can lead to palatability issues.

Silage preservation quality can be quantified by submitting samples to forage laboratories that offer fermentation profile tests and yeast/mold colony-forming unit enumerations and identifications.

Corn silage should be primarily fed based on its carbohydrate contribution for meeting energy needs of cattle. This is because 70 to 80 percent of nutrient makeup in corn silage is carbohydrate from neutral-detergent fiber (NDF), starch and sugars.

Many producers value corn silage for its protein contribution. However, the average crude protein content from Dairyland Laboratories 2012 Summary was 7.8 percent, and the value ranged from 5 to 10.5 percent. That value pales in comparison to the high carbohydrate value of corn silage.

NDF contribution from corn silage in the ration needs to be assessed for its degree of NDF digestibility (NDFD) and physical effectiveness of the NDF (peNDF) for stimulating rumination and cud chewing by the dairy cow to maintain rumen health and function.

Ration design involves balancing for the pounds of NDF and not just the percentage. For corn silage, percentage of NDF content declines with higher starch content due to dilution. A high-starch corn silage inclusion will require extra pounds of NDF from other forage sources.


Nutritionists are beginning to understand that NDFD is only a guide, and even the best labs have about a two to three percentage point variation in estimates associated with these values. This is why monitoring absolute pounds of forage NDF intake and paying close attention to the condition of the manure continues to guide the ration adjustments of many field nutritionists.

Analytical assessments of NDF forage quality has improved thanks to research efforts in recent years. Many nutritionists are using forage laboratory offerings for undigestible NDF (uNDF) usually at 30-, 120- and 240-timepoints in addition to traditional NDFD measurements. The three timepoint uNDF measurements can be used in computer models to calculate the kinetic digestion rate of NDF (Kd, NDF) in corn silage, which is more meaningful than just testing corn silage for NDFD at one timepoint. A direct test for Kd laboratory offerings exists, known as Fermentrics. In addition, potentially digestible NDF (pdNDF) is another calculation based on known uNDF and NDF values that nutritionists can use to compare corn silage quality differences.

Nutritionists feeding high-corn silage rations tend to feed slightly higher levels of NDF in the entire ration. Research indicates that 30 percent NDF in the dairy ration can be fed in high-corn silage rations without loss of milk production.

In dairy rations where peNDF levels are tracked, most high-corn silage herds prefer balancing at 23 to 24 percent peNDF, which is at the high end of typical 21 to 24 percent peNDF recommendations. The peNDF assessment of the ration can be obtained from several forage testing laboratories or by using the Penn State separator system equipped with a 1.18-mm stainless steel screen.

Starch concentration, starch digestibility (STRD), kinetic rate of starch digestion (Kd, starch) and degree of kernel processing (KP) in corn silage impact starch availability to rumen microbes and resulting dairy cow performance and health.

Depending on starch content, and thus energy value, corn silage can be targeted to a wide range of livestock groups. High-starch corn silage is required for high-producing dairy cows, while low-energy corn silage is required for low-producing dairy cattle, dairy replacement heifers or dry cows.

High corn silage inclusion rates can provide excessive fermentable carbohydrates to the rumen and result in acidotic events. However, with the advent of laboratory starch, STRD, starch Kd and KP analyses, producers can implement tighter control over ruminal starch digestion by adjusting the supplemental grain sources in the ration.

Research trials find that STRD increases with longer silo storage time. By monitoring starch, STRD, starch Kd and KP throughout silage feedout, appropriate ration adjustments can be made for desired levels of ruminal starch availability.

Corn silage contains about 3.5 to 4 percent fat, while high-oil hybrids will contain 6 to 8 percent fat. The fats from corn silage are highly available to the rumen, and if fed with excessive supplemental tallow or distillers grains, dairy cows can show reduced dry matter intakes and butterfat depression.

Research shows the dairy butterfat depression issue stems from the amount of trans-fatty acids fed in the ration. High-corn silage inclusion rations require close attention to levels of polyunsaturated fatty acids (PUFA) in the ration, which can be done by nutritionists with software programs that monitor PUFA, specifically linoleic acid.

Protein conservation opportunities exist when feeding high-corn silage rations if it's known how much of the protein is ruminally digestible protein (RDP) utilized by rumen microbes for microbial growth and reproduction.

A nutritionist's goal is to successfully match rumen microbe needs for fermentable starch with RDP. At that point, increased amounts of microbial protein will be produced that the ruminant will utilize for maintenance, growth, reproduction and milk production.

Cornell research recently showed that unused RDP is absorbed into the blood system and that a percentage of it will be recycled back to the ruminant via saliva. Being able to closely monitor the amount of RDP in the ration permits a lower-crude protein ration that offers protein supplement cost savings.

In comparison to other forage crops, corn silage is the most cost-efficient forage source on a per-acre basis that growers can produce. Therefore, striving to maintain corn silage consistency and maximizing nutrient utilization from the crop enterprise will result in higher production efficiencies when it comes to dairy production enterprises. PD

PHOTO: Photo by Alan Leavitt.

Bill Seglar
  • Bill Seglar

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