Harvesting and Storing Corn Silage

by Dr. Clay Zimmerman

Since corn silage is a major component of many dairy rations, we need to make every effort to produce the best quality silage both chemically (nutrient content) and physically (particle size).

When is the proper time to chop corn silage? Harvest corn silage when the moisture content is correct. Moisture content should be 65-70% for tight silo packing and optimal fermentation in a bunker silo or bag. Corn silage should be harvested at 63-68% moisture for an upright stave silo and 55-60% for an upright sealed silo. If corn silage is harvested at >72% moisture it may cause excessive seepage and can lead to butyric acid fermentation. If silage is harvested too dry, it will not pack well and aerobic respiration can occur. In addition, we want corn silage to be harvested when the milk line is at 1/3 to 2/3, but proper plant moisture should be the first criteria for chopping.

What should be the theoretical length of cut (TLC) for corn silage? It depends. Recommended TLC for unprocessed corn silage is 3/8 to 1/2". If corn silage is the primary forage in the diet and is being counted on to provide effective fiber, TLC should be closer to 1/2". If not much corn silage is fed and it is not needed for effective fiber, 3/8" corn silage will have a slightly higher digestibility. If corn silage is processed through a kernel processor, recommended TLC is 3/4".

Once we've harvested the silage at optimal maturity, we need to take every precaution possible to achieve desirable fermentation to preserve corn silage. The following four steps are extremely important:

1. 1. Fill rapidly
2. 2. Use a good quality inoculant
3. 3. Level and pack quickly and adequately
4. 4. Cover with a plastic sheet and weight down as soon as filling is complete

Rapid filling is critical to minimize exposure to air. Air exposure promotes aerobic respiration that can lead to excessive heating, molding and heat damage, which lowers the nutritive value of silage. Rapid filling will also prevent the off-color streaks that you often see in silage piles.

A good quality inoculant is important for corn silage because it can often improve the quality of silage and it does aid in preservation. Inoculants serve to prevent catastrophic losses in corn silage which can occur every few years. Our Silage Supreme™ 3X silage inoculants contain equal levels of two bacterial species, Lactobacillus plantarum and Pediococcus pentosaceus.

Lactobacillus plantarum produces large amounts of lactic acid and survives at mildly acidic conditions, taking over when the pH drops below 5. Pediococcus pentosaceus begins the fermentation process and gives a fast drop in pH. A good inoculant will produce a faster fermentation, produce more lactic acid and generate less heat.

Leveling and packing the silage quickly and adequately is one point that is often overlooked today. With the advent of custom silage harvesters and large, self-propelled choppers, many silos are filled way too fast for adequate packing. Again, it is important to do a good job of packing to quickly eliminate air from the silage. How fast can you fill a bunker silo? Take the weight of the tractor and divide by 800 and the result is your maximum filling rate in tons/hour. For example, if you have a 24,000 lb packing tractor divided by 800 = 30 tons per hour maximum filling rate. If you want to fill faster than this, you either need a heavier tractor or have more than 1 tractor packing at the same time.

Covering the silage quickly and completely after filling is extremely important to minimize dry matter losses during storage. If left uncovered, dry matter losses in the top 1 to 3 feet of a bunker silo can exceed 60-70% compared to 12% loss if the feed is covered. It has been estimated that covering bunker silos can result in a 2:1 to 8:1 payback depending upon actual spoilage losses. When the silo is opened, it may appear that only 4 to 6 inches have spoiled, but remember that every inch of crust at feed-out probably represents 3 inches of original silage so that 4-6 inches of spoiled silage may represent 1 to 1.5 feet of original silage. Remember that when the surface spoils, it not only results in rotten feed, but it can also decrease the nutrient availability of the good silage. A Kansas State University study published in 2000 demonstrated the effects of feeding spoiled corn silage to beef steers. They fed 4 different diets that were 90% corn silage and 10% supplement on a dry matter basis. The 4 diets differed in the amount of spoiled silage that was fed. The results are as follows:

It is clear from these data that spoiled corn silage reduced feed intake and the digestibilities of all nutrients in the diet. Feeding the spoiled silage had a greater negative impact than expected because of the decreased nutrient digestibilities. They also observed that steers fed the spoiled silage had partially or totally destroyed forage mats in the rumen.

Once all of this is accomplished, the last step is to maintain a clean face surface on the silo during feed-out. Make sure that bunker silos have a smooth surface and that you are removing at least 6"/day from the face during summer and at least 4"/day during the winter to minimize surface spoilage.

You will always have some dry matter losses when making corn silage (typically about 10% of DM is lost from respiration, harvesting and feed-out losses). The key is to do a good job of silage storage to minimize the storage losses that can occur. Our goal is to keep storage losses at 10% or less of the dry matter.

Other goals for stable corn silage:

Will there be issues with the drought stressed corn silage that was harvested in some areas? There may be. The first thing to realize is that forage quality will be lower than usual, particularly if there is no grain in the silage. If there is no grain in the silage, it will probably feed similar to mediocre grass silage. The second issue could be nitrates. Nitrates can be a problem in drought stressed forages, particularly when you get a nice rain before harvest. If you are in a dry area it would be a good idea to check your first few corn silage samples for nitrates. If they show up negative, it's a good bet that nitrates aren't an issue in your area unless you hear of other dairies in the area with a problem. Also beware of silo gas in upright silos if nitrates are an issue. The gas (nitrogen dioxide) has a yellowish-brown haze. To minimize the effects of silo gas, run the silo blower for 30 minutes before entering the silo and keep the blower running while you are in the silo.

© September, 2001. Blue Seal Feeds, Inc.

© Blue Seal Feeds – September, 2001