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Proper Harvest Critical to Making Silage

NDSU’s dairy specialist offers tips for making good corn silage.

Many producers growing corn for silage are ready to chop, but the corn may not be at the correct moisture level.

“Harvesting corn silage at the correct moisture is critical for feed quality,” says J.W. Schroeder, North Dakota State University Extension Service dairy specialist. “The best livestock performance and corn silage fermentation usually occur when whole-plant moisture is 65 percent to 70 percent. This corresponds well to horizontal and bag silos, but silage may have to be somewhat drier in tall tower silos to prevent seepage.”

When forage is put into a silo, conditions are aerobic (oxygen is present in the silage mass). Aerobic bacteria produce some heat as they break down carbohydrates and sugars into carbon dioxide and water and use up the trapped oxygen.

When the oxygen has been consumed, the silage becomes anaerobic, which promotes the growth of anaerobic bacteria. These organisms convert the carbohydrates and sugars to organic acids that preserve the silage.

In addition, some of the protein is broken down into amino acids, ammonia and other nonprotein nitrogen compounds. During this ensiling process, the acids lower the pH (a measure of acidity or alkalinity), while the production of ammonia tends to raise it. The production of ammonia increases the amount of time needed to reach a stable pH.

In two or three weeks, the silage reaches a stable pH of 4 to 5 and all bacterial and enzymatic activity stops. Once this stable pH has been reached, further breakdown of nutrients and spoilage is prevented, and the silage will keep for extended periods of time, provided air is excluded.

Several management practices are important for preserving high-quality silage. Many of these practices help decrease the amount of air trapped in the silage mass. They include:

  • Sharpen knives. Sharp knives prevent silage from being shredded, resulting in a more uniform chop. This allows for maximum forage compaction, good fermentation and sufficient particle size to prevent health problems in the cow.
  • Make sure the corn is at the proper moisture content (stage of maturity) at harvest. For bunkers, silage should contain from 30 percent to 35 percent dry matter or 65 percent to 70 percent moisture. Silage in upright silos can be a little drier, at 35 percent to 40 percent dry matter or 60 percent to 65 percent moisture. Silage that is too wet when it’s stored results in a butyric acid-type fermentation, which decreases feed intake and can result in ketosis in early lactation cows. Silage that is too dry will have more and larger air pockets, which results in a poorer fermentation and less beneficial acids for cows to use to make meat and milk.
  • Chop the corn to the correct length. Silage needs to be chopped fine enough for good packing to quickly eliminate oxygen and establish a good fermentation process. At the same time, the chop length needs to be long enough to promote cud chewing by the cows. Thus, the recommended theoretic length of chop (TLC) is a compromise between these two factors. By comparison, alfalfa haylage should be chopped at three-sixteenth inch, unprocessed corn silage at three-eighths to one-half inch and processed (kernel processor) corn silage at three-fourths inch. (Brown-midrib corn silage should be chopped longer than these TLC.)
  • Fill silos quickly to help eliminate air from the feed.
  • Pack, pack and pack some more. Tightly-packed silage ferments more quickly and contains less yeasts and molds than loosely packed silage. Packing silage helps decrease the size of oxygen pockets, resulting in fermentation with end products the cow can use to make milk. For a bunker, experts recommend that when you think you are done packing, you should pack that much more. The most desirable method of packing bunker silos is the progressive wedge method, where silage is packed continually on a 30 percent to 40 percent grade. This minimizes the surface area that is open to exposure to the air, which can result in dry-matter and forage-quality losses. If this is not possible, then silos should be packed by spreading relatively thin layers of silage (6 inches deep) and packing it well. If packed well, the silage should have a density of about 14 pounds of dry matter per cubic foot. For silage stored in a bag, monitoring the diameter of the bag is important to achieve the proper packing density.
  • Cover silos immediately after filing. Bunkers or piles of silage need to be covered with 6-mil plastic tarps and weighted with tires (tires should touch each other) immediately after filling. Upright silos should be leveled and capped with a silo cap immediately after filling is complete. Uncovered silos lose a tremendous amount of feed and feed nutrients.
  • Let silage ferment three to four weeks before feeding if possible. Unfermented feed is higher in fermentable sugars and can cause cows to go off-feed. Gradually transition cows to new fermented silage in 10 days if possible or use dry hay to buffer cows through the transition.

NDSU Agriculture Communication

Source:J.W. Schroeder, (701) 231-7663, jw.schroeder@ndsu.edu
Editor:Ellen Crawford, (701) 231-5391, ellen.crawford@ndsu.edu
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