Kernel processed corn silage

Forage harvesters can be equipped with kernel processors to crack corn kernels. Processing can improve kernel digestibility, especially when kernels are mature. Processors also break the cobs increasing cob consumption by the cow. The crushing of the plant improves silo compaction, allowing for increased length of cut. The economical advantage of a kernel processor is dependent on the percent corn silage in the ration, the number of cows being fed corn silage, and the typical speed and timeliness of harvest.

Forage harvesters can be equipped with kernel processors to improve the digestibility of hard, mature kernels in corn silage. Kernel processors are counter-rotating rollers that are intended to crack corn kernels as they pass from the cutterhead to the blower. A less popular method of processing corn silage at harvest is with a recutter screen. Recutter screens basically cut the whole plant up more, reducing the effective fiber value of the corn silage. Stationary roller mills are also sometimes used to process corn silage as it comes out of the silo, but this is less common.

Why Would Kernel Processors Be Needed?

Corn will sometimes get too mature in the field. One of the biggest problems with mature corn is that the corn kernels get hard (you can no longer break them with your fingernail) and less digestible (the kernels pass through the cow and show up in the manure). Researchers have reported that as much as 25% of the corn kernels in corn silage may pass out of the cow in the manure. That is energy that will be fed to wild turkeys in the field rather than being used for milk production!

Effect of Maturity of Unprocessed Corn Silage on Nutritive Value for Milk Production

  ½ Milk Line Black Line
Milk (pound/day) 47.1 44.2
Milk (kg/day) 21.4 20.1
Corn in Feces (%DM) 3.1 9.0
Starch Digestion in the Rumen (%) 72 56
Starch Digestion in the Whole Cow (%) 96 87

* All reported differences were statistically significant (P<0.05)
(Harrison, 1996)

Other reasons exist for processing corn silage. Processing can improve the silage fermentation by increasing the starches and sugars available to the silage microorganisms. This reduces dry matter losses in the silo. Processing also helps to break the cobs up. This leads to fewer cobs being left behind as orts in the feedbunk, reducing waste, making the cow eat what she’s actually offered, and improving fiber consumption. Also, cob breakage may lead to an improvement in fiber digestibility. Finally, the crushing of the plant improves its compaction in the silo and allows one to increase the length of cut of the corn silage, increasing the amount of effective fiber.

There are a number of reasons why corn may get too mature. Some hybrids mature rapidly. Frost will also cause rapid dry down. Sometimes it’s just hard to get machinery onto fields at the right time for harvesting because of muddy conditions. Finally, some farmers may choose to harvest more mature corn because of increases in grain content and dry matter yield associated with mature corn at black line. If they can purchase a hybrid that maintains stover digestibility as it matures and then process it, they may come out ahead economically.

Processing Effects on Ensiling Quality:

Washington State University researchers (Harrison et al., 1997) harvested corn silage at three levels of maturity (Dough (23% DM), 1/3 Milk Line (28% DM), and 2/3 Milk Line with a killing frost (30% DM) and either processed them using a John Deere 5830 or didn’t process them. Processing had little effect on the pH decline of the less mature (Dough and 1/3 Milk Line) silage. But, processing caused the corn silage harvested at 2/3 Milk Line to ferment faster and have a lower pH after 10 days.

Processing Effects on Nutritive Value:

The effect of kernel processing can be evaluated be placing corn silage samples as received (without further grinding) into dacron bags and hanging the bags into the rumen of a fistulated cow for the amount of time it expected to normally stay in the rumen of the cow. This is called the in situ technique. Sometimes labs will grind up samples prior to analysis. This, of course, obscures digestibility differences due to kernel processing and should not be done.

Effect of Processing on In Situ Digestibility of Corn Silage

  Unprocessed Processed
Dry Matter Digestibility (%) 50.4 62.2
NDF Digestibility (%) 24.1 36.3
Starch Digestibility (%) 53.3 75.7

Processing differences were statistically significant (P<0.05)
Source: Hunt, C. 1996 (Unpublished) from Harrison et al., 1997

In research studies with processed versus unprocessed corn silage, milk production has improved by 0.44 to 4.4 pounds/day (0.2 to 2 kg/day) with processed corn silage. Milk protein also usually increases, probably because of an increase in microbial protein synthesis from greater starch digestion in the rumen.

Particle Size:

Depending on the type of processor, there may be a shearing effect as well as a crushing effect. This may have an impact on the particle size of the corn stover and must be carefully watched. For a particular theoretical length of cut (TLC) on a chopper, kernel processors can decrease particle size by 15-30%. Dr. Bill Mahanna of Pioneer Hi-Bred International, Inc. recommends that unprocessed corn be cut at a TLC of 3/8 – ½ inch (9.5-12.7 mm) resulting in 15-20% of the particles being greater than ½ inch (12.7 mm). When processing corn silage, he recommends that if corn silage will make up over 40% of the ration dry matter, increase TLC to ¾ inch (19.1 mm) by manipulating the shear bar or by removing knives from the chopper. This will allow one not to rely as much on hay crop silage for ration effective fiber.

Dr. Bill Weiss at The Ohio State University, looked at the particle size distribution of unprocessed corn silage (3/8 inch TLC (9.5 mm)) vs. processed corn silage (3/4 inch TLC (19.1 mm) with a roll clearance of 1 mm). He found that the unprocessed corn silage had only 5% of the total dry matter remaining on the top screen of the Penn State Forage Separator, 80% on the middle screen, and 15% on the bottom. With the processed corn silage, 20% of the dry matter remained on the top screen, 60% was on the middle screen, and 20% remained on the bottom. There wasn’t much difference in the distribution of starch and NDF from total dry matter in the unprocessed corn silage. But, with the processed corn silage, there was a larger percentage of NDF on the top screen and a larger percentage of starch on the bottom. Weiss also determined that the TDN content (%) of the processed corn silage was 8% (percent not percentage units) higher than the unprocessed corn silage.

Does Kernel Processing Pay?

The decision whether or not to purchase a kernel processor is not always easy. It depends on a number of factors, including, how large of a percentage of the ration is corn silage, the number of cows being fed corn silage, and the typical speed and timeliness of harvest. In good years where corn silage can be harvested on time (1/2 milkline, 70% moisture), kernel processing won’t have as great of an impact. In poor years with overly mature corn to harvest, kernel processors can pay big dividends.

Penn State researchers have developed equations to predict the depression in energy associated with overly mature corn silage. They suggest that the adjusted energy values be used if they are lower than the unadjusted values. Generally, the adjusted energy values will be used when corn silage is greater than 35% DM and about 2/3 milkline.

Corn Silage Energy (unadjusted)
NEl = 1.044 – (0.0124 x ADF)
TDN = 31.4 + (53.1 x NEl)

Adjusted Corn Silage Energy
TDN = 92.49 + (-0.6525 x DM)
NEl = (Adjusted TDN – 31.4) / 53.1

Comments from Dairy Farmers:

Most producers who have tried kernel processors on mature corn silage have liked the results. They see less corn in the manure, less cobs left in the feedbunk, and increased milk production. Farmers, especially custom operators, like having the longer harvest window. They have found that they can chop the silage longer to obtain more effective fiber and it still packs well after processing.

Some farmers have had more acidosis problems with processed corn silage. Kernel processing makes the starch available more quickly for the rumen microbes. Especially if the corn is not at blackline and if there are other sources of rapidly available starch or sugar (like from molasses, bakery product, flour or high-moisture shelled corn) in the ration, processing corn silage could actually decrease milk production because of increased rumen acidity and poor rumen health. Remember that the rumen microbes want a blend of rapidly and slowly available starches and sugars. Too much rapidly available starch and sugar will cause acidosis even if the total amount of non-fiber carbohydrate (NFC) in the ration is under reasonable (<40% of the ration DM).


Adams, R.S. et al., 1995. Dairy Reference Manuel. NRAES-63, Third Edition, Ithaca, NY, p. 108.

Harrison, J.H., L. Johnson, R. Riley, S. Xu, K. Loney, C.W. Hunt, and D. Sapienza. 1996. Effect of harvest maturity of whole plant corn silage on milk production and component yield, and passage of corn grain and starch into feces. J. Dairy Sci. 79:149 (Suppl. 1).

Harrison, J.H., L. Johnson, C. Hunt, J. Siciliano-Jones, and K.J. Shinners. 1997. Use of kernel-processed silage in dairy rations. Proceedings of the Silage:Field to Feedbunk North American Conference, Hershey, Pennsylvania.

Johnson, L., J.H. Harrison, C. Hunt, K. Shinners, C.G. Doggett, and D. Sapienza. 1999. Nutritive value of corn silage as affected by maturity and mechanical processing: A contemporary review. J. Dairy Sci. 82:2813.

Mahanna, B. 1997. Dairy Cow Nutritional Guidelines – Part 1. Pioneer Hi-Bred International, Inc. Website (

Weiss, B. 2000. Processed corn silage becomes a different feed. Hoard’s Dairyman. August 10, 2000, p. 532.

Related links:

Effect of Oil Content and Kernel Processing on the Nutritional Value of Corn Silage for Dairy Cows (A Research Report)
W.P. Weiss, Ph.D., Ohio State University


Mary Beth de Ondarza

Mary Beth de Ondarza
45 articles

Nutritional consultant for the dairy feed industry at Paradox Nutrition, LLC.

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Paradox Nutrition

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Paradox Nutrition, LLC is a nutritional consultation business for the dairy feed industry. Mary Beth de Ondarza, Ph.D. is the sole proprietor.

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