Does corn silage fed to feedlot cattle need to be kernel processed?

Processing corn silage can improve corn kernel damage and increase starch digestibility when fed to cattle; however, the expected increase in feedlot performance may be minimal.

Cows eating corn silage
Holstein steers consuming a diet containing corn silage.

It’s that time of year again when corn across the Midwest is beginning to reach the ideal maturity needed to produce corn silage. Many producers often question how they can produce the highest yielding or quality crop. A review by Johnson and others in the Journal of Dairy Science report that mechanically processing your corn silage may be an option to improve the quality or feeding value of your corn silage crop. More information regarding corn silage can be found on the Michigan State University Extension corn website.

Fully active mechanical processors are most common and consist of two counter rotating rollers located between the cutterhead and the blower of the harvester. The grooved or serrated rollers crush or shear the corn silage as it passes between the two rollers with a space typically ranging from 1 to 5 mm. However, additional energy (7 to 15%) is required and there is a reduced harvest capacity by the harvester (0 to 28%) when mechanically processing corn silage. The use of recutter screens can also be used but are less common because they produce corn silage with a much finer particle size. Another option for mechanically processing corn silage is with the use of a stationary roller mill which can allow for mechanical processing of corn silage to occur before or after ensiling.

Silage Characteristics

Kernel processors for corn silage are used to cause damage to the corn kernel for improved starch utilization by the animal. Processing corn silage decreases the number of undamaged whole corn kernels. However, corn silage particle size is reduced 15 to 30% as a result of kernel processing. Therefore, when processing corn silage, the recommended theoretical length of cut (TLC) is typically greater than for unprocessed corn silage. The desired TLC will depend heavily on your diet composition. Corn silage is the most commonly used roughage source in Midwest feedlot rations, providing a source of fiber to help prevent digestive disorders such as acidosis.

The chemical compositional differences of processed and unprocessed corn silage are less evident. The finer particle size of processed corn silage may pack more tightly, resulting in improved fermentation of readily fermentable substrates. This causes a lesser pH, greater lactic acid production, and slightly greater fiber (neutral detergent fiber [NDF], acid detergent fiber, lignin) percentage compared with conventional corn silage after ensiling. However, these differences are small and may be more heavily influenced by other factors such as hybrid variety, maturity stage, and TLC than mechanical processing.

In a different Journal of Dairy Science article by Johnson and others, researchers demonstrated that corn plant growth can vary by the year, mainly due to precipitation and temperature differences. In the study, rumen digestibility of corn silage was affected by hybrid variety (high vs. low NDF), corn plant maturity at harvest (ranging from hard dough to black layer), use of mechanical processing (kernel processed vs. unprocessed), and the TLC (ranging from 0.375 to 1.5 inches).

The use of a kernel processor while harvesting silage influenced dry matter (DM), starch, NDF, and crude protein digestibility within the rumen. Dry matter digestibility of mechanically processed corn silage is greater than unprocessed corn silage because of the increased digestibility of starch, particularly in corn silage harvested at a later maturity and for low NDF corn silage varieties as well.

The reason to mechanically process corn silage is because of the greater starch digestibility due to the increased damage caused to the corn kernel. Damage to the tough exterior (pericarp) of the corn kernel allows the rumen microbes access to the starch inside the corn kernel resulting in a greater total tract starch digestibility by the animal. Processing corn silage demonstrated less of an improvement for NDF digestibility. However, when harvested at a later maturity, processing corn silage improved NDF digestibility compared with unprocessed corn silage. Fiber (NDF) digestibility of corn silage produced during hot and dry years as compared with cool and wet years was greater with processing. Similar to NDF digestibility, crude protein digestibility demonstrated little improvement from processing, except for mature corn or corn silage with a shorter TLC.

A Professional Animal Scientist paper, by Ferraretto and Shaver from Wisconsin compiled the results from multiple studies and summarized corn silage harvesting practices effects on digestion and milk production in dairy cows. Kernel processing resulted in 8% whole corn kernels compared with 19% whole corn kernels in unprocessed corn silage. Kernel processing resulted in a greater organic matter digestibility with rollers set either 1 to 3 mm or 4 to 8 mm apart compared with unprocessed corn silage. Total tract starch digestibility was greater for corn silage that was kernel processed at 1 to 3 mm compared with 4 to 8 mm and unprocessed corn silage. Kernel processing effect on total tract starch digestibility is also influenced by TLC and DM content, where DM content may be an indicator of corn plant maturity at harvest. Total tract starch digestibility was greater for kernel processed corn silage compared with unprocessed corn silage when the DM content was between 32 to 40%, and the TLC was between 0.375 to 1.125 inches.

Feeding Performance

While the effect of feeding feedlot steers processed versus unprocessed corn silage has not been extensively researched, the few studies investigating this topic are shared below. In one study conducted by Ovinge and others, published in a Nebraska Beef Cattle Report, feeding processed corn silage at 40% of the diet DM, resulted in a lesser DM intake (0.8 pounds per day) and similar average daily gain (4.4 pounds per day) for yearling crossbred steers. This tended to improve feed efficiency 2.8% for cattle offered corn silage that was kernel processed. Therefore, processed corn silage offered a greater amount of available energy to be used for body weight gain. No differences were observed for carcass traits or diet digestibility due to kernel processing corn silage at harvest. Corn silage used in this study was harvested at a three-quarter milkline maturity, with a 0.75-inch TLC, and 2 mm kernel processing.

Conroy and others, published in a Nebraska Beef Cattle Report, processed corn silage with different TLC (0.51 vs. 1.04 inches) and 1 mm kernel processing was compared and offered at either 9 or 14% of the diet DM to yearling crossbred steers. Offering processed corn silage with a greater TLC resulted in greater and more efficient body weight gains for cattle due to the associative effects of the longer particle length of the corn silage in combination with a high steam flaked grain diet. No differences were observed for carcass traits due to kernel processing corn silage at harvest.

A study published in Journal of Animal Science by Rojas-Bourrillon and others from Iowa reportedly failed to observe a performance and digestibility difference between processed (harvested at black layer maturity, 0.375 inch TLC, and with 0.3 mm kernel processing) and unprocessed corn silage in backgrounding diets offered to crossbred steer calves. The lack of differences between the processed and unprocessed corn silage may have been due to an 8.2% lesser ruminal retention time for solid feed particles from processed corn silage to be digested compared with unprocessed corn silage.

A conference proceeding presented at Cattlemen’s Day by Young and others from Kansas State University compared feeding mechanically processed (pre- or post-ensiled) with conventional unprocessed corn silage to crossbred steers and heifers in a backgrounding diet consisting of 90% corn silage. Corn silage was harvested in the black layer stage (mature) and chopped at a 0.375-inch TLC. Offering calves processed (pre- or post-ensiling) corn silage for 80 days resulted in a greater ADG, and a more desirable feed efficiency (+7.1%) compared with unprocessed corn silage. Numerically, DM and NDF digestibility was improved by processing, while corn silage processed after ensiling had the greatest starch digestibility when fed to cattle.

Final Thoughts

When kernel processing adequately damages the corn kernels in corn silage, starch digestibility is improved, especially when corn silage is harvested at a greater maturity. Very few studies have investigated the effects of kernel processed corn silage on feedlot cattle performance. In general, results of feedlot performance differences between processed and unprocessed corn silage have been very small or non-existent. Theoretically, as the contribution of corn silage in the diet increases, the beneficial effects of kernel processing are more likely to be realized due to the increased starch digestibility. However, kernel processing has not demonstrated consistent improvements in feedlot performance when cattle were offered finishing diets with a low corn silage inclusion or backgrounding diets with a greater corn silage inclusion. Overall, you must determine if the slight improvements in feed efficiency from kernel processing corn silage justify the added expense of purchasing a kernel processor for your operation.

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