Read the current Progressive Forage digital edition

0807 PD: Avoid common silage pitfalls

Keith K. and Ruthie Bolsen Published on 07 August 2007

Regardless of the size of an operation, dairy producers know problems occur in every silage program. This [article] describes possible causes and solutions for eight common pitfalls, which include.

Dairy producers (and their nutritionist) should discuss these problems and solutions with everyone on their silage team as a reminder to implement the best possible silage management practices.

#1 Safety issues for bunker silos and drive-over piles

Consistently protecting workers, livestock, equipment and property at harvest, filling and feeding does not occur without thought, preparation and training. You have nothing to lose by practicing safety; you have everything to lose by not practicing it.

Major hazards and preventive measures

Tractor roll-over

•Roll-over protective structures (ROPS) create a zone of protection around the tractor operator. When used with a seat belt, ROPS prevent the operator from being thrown from the protective zone and crushed by the tractor or equipment mounted on or drawn by the tractor.

•A straight drop-off from a concrete retaining wall is a significant risk, so never fill higher than the top of a wall.

•Install sighting rails on above-ground walls. These rails indicate the location of the wall in relation to the tractor operator but are not to hold an overturning tractor.

•Consider adding lights to the rail, if filling will occur at night.

•Form a progressive wedge of forage when filling bunkers or piles. The wedge provides a slope for packing, and a maximum 3-to-1 slope minimizes the risk of a tractor roll-over.

•Backing up the slope can prevent rollbacks on steep slopes.

•Use low-clearance, wide front end tractors and add weights to the front and back of the tractors to improve stability.

•When using front-end loaders to carry feed into the silo, do not carry the bucket any higher than necessary in order to help keep the center of gravity low.

•Front-wheel and front-wheel-assist drive tractors provide extra traction and stability.

•When two or more pack tractors are used, establish a driving procedure to prevent collisions.

•Dump trucks, which are used to transport chopped forage in large-scale operations, can roll over on steep forage slopes, particularly if the forage is not loaded and packed uniformly.

•Raise the dump body only while the truck is on a rigid floor of the storage area to prevent turnovers.

Entangled in machinery

•Keep machine guards and shields in place to protect the operator from an assortment of rotating shafts, chain and v-belt drives, gears and pulley wheels, rotating knives on tractors, pull-type and self-propelled harvesters, unloading wagons and feeding equipment.

Runover by machinery

•Never allow people on foot (especially children) in or near a bunker or pile during filling.

•Properly adjust rear-view mirrors on all tractors and trucks.

Fall from height

•It is easy to slip on plastic when covering a bunker, especially in wet weather, so install guardrails on all above-ground walls.

•Use caution when removing plastic and tires, especially near the edge of the feeding face.

•Never stand on top of a silage overhang in bunkers and piles, as a person’s weight can cause it to collapse.

Crushed by an avalanche or collapsing silage

•The number one factor contributing to injuries or deaths from silage avalanches is overfilled bunkers and drive-over piles.

•Do not fill higher than the unloading equipment can reach safely. Typically, an unloader can reach a height of 12 to 15 feet.

•Use proper unloading technique that includes shaving silage down the feeding face. Never ‘dig’ the bucket into the bottom of the silage. This is called undercutting. It is a situation quite common when the unloader bucket cannot reach the top of an overfilled bunker or pile, creating an overhang of silage that can loosen and tumble to the floor.

•Never allow people to stand near the feeding face, and a rule-of-thumb is never being closer to the feeding face than three times its height.

•Fence the perimeter of bunkers and piles and post a sign, “Danger: Do Not Enter. Authorized Personnel Only.”


•Think safety first! Even the best employee can become frustrated with malfunctioning equipment and poor weather conditions and take a hazardous shortcut or misjudge a situation and take a risky action.

•It is always best to take steps to eliminate or control hazards ahead of time rather than rely upon yourself or others to make the correct decision or execute the perfect action when a hazard is encountered.

#2 High ‘forage in’ versus ‘silage out’ losses in bunker silos, drive-over piles and bags


•Select the right forage hybrid or variety.

•Harvest at the optimum DM content.

•Use the correct size of bunker or pile, and do not overfill bunkers or piles.

•Employ well-trained, experienced people, especially those who operate the forage harvester, pack tractor or bagging machine. Provide training as needed.

•Apply the appropriate bacterial inoculant.

•Achieve a uniform packing density in bunkers and piles (a minimum of 15 pounds of DM per cubic foot).

•Provide an effective seal to the surface of bunkers and piles and consider using double polyethylene sheets or an oxygen barrier (OB) film.

•Follow proper face management practices during the entire feedout period.

•Start a silage quality control program and schedule regular meetings with your team.

#3 Large variation in the DM content or nutritional quality of the ensiled forage


•interseeded crops of different maturity

•multiple cuttings or multiple forages ensiled in the same silo

•delays in harvest activities because of a breakdown or shortage of machinery and equipment

•seasonal or daily weather effects on crop maturing and field-wilting rates

•differences among corn hybrids Solutions

•Use multiple silos and smaller silos that improve forage inventory control.

•Ensile only one cutting or variety of ‘haycrop,’ field-wilted forage per silo.

•Minimize the number of corn or sorghum hybrids per silo.

•Shorten the filling time, but do not compromise packing density.

#4 Missing the optimum harvest window for whole-plant corn


•Harvest equipment capacity is inadequate or the crop matures in a narrow harvest window.

•Warm, dry weather can speed the maturing process and dry-down rate of the crop.

•Wet weather can keep harvesting equipment out of the field.

•Sometimes it is difficult to schedule the silage contractor.


•Plant multiple corn hybrids with different season lengths.

•Improve the communication between the dairy, crop grower and silage contractor.

•Change harvest strategy, which might include kernel processing, shorter theoretical length of cut (TLC) or adding a pack tractor.

#5 Clostridial, butyric acid- containing hay-crop silage


•The forage is ensiled too wet and undergoes a fermentation dominated by clostridia.

•Alfalfa and other legumes that experience a rain event in the field after mowing are at a higher risk because rain leaches soluble sugars from the forage.

•The forage is harvested too wet for the type and size of storage.


•Chop and ensile all forages at the correct DM content for the type and size of silo.

•Proper packing to achieve a minimum density of 15 pounds of DM per cubic foot excludes oxygen and limits the loss of plant sugars during the aerobic phase.

•Apply a homolactic bacterial inoculant (HLAB) to all forages to ensure an efficient conversion of plant sugars to lactic acid.

•Do not contaminate the forage with soil or manure at harvest.

•If it is not possible to control the DM content by wilting in the field, the addition of soluble sugars can reduce the chance of clostridial fermentation and the problems associated with butyric acid silages.

#6 High levels of acetic acid, particularly in wet corn silage

Causes and symptoms

•If the whole plant has a low (dry matter) DM content, it is predisposed to a long, heterolactic fermentation.

•This silage has a strong vinegar smell, and there will be a 2- to 3-foot layer of bright yellow, sour-smelling silage near the floor of a bunker silo or drive-over pile.


•Ensile all forages at the correct DM content, especially not too wet.

•Use a HLAB inoculant to ensure an efficient conversion of plant sugar to lactic acid.

#7 Aerobically unstable corn silage during feedout

Research has not explained why corn silages differ in their susceptibility to aerobic deterioration. Microbes, primarily lactate utilizing yeast, as well as forage and silage management practices contribute to aerobic stability of an individual corn silage.


•Harvest at the correct stage of kernel maturity, especially not too mature.

•Ensile at the correct DM content, especially not too dry.

•In normal conditions, do not chop longer than 0.75-inch TLC if the crop is processed or 0.5-inch if not processed.

•Achieve a minimum packing density of 15 pounds of DM per cubic foot.

•Maintain a uniform and rapid progression through the silage during the entire feedout period. Remove a minimum of 6 to 12 inches per day in cold weather months and 12 to 18 inches per day in warm weather months.

•Minimize the time corn silage stays in the commodity area before adding it to the ration. It might be necessary to remove silage from a bunker silo or drive-over pile and move it the commodity area twice daily.

•Do not leave corn silage rations in the feedbunk too long, especially in warm, humid weather.

•Add 2 to 4 pounds of a buffered propionic acid product per ton of total mixed ration, if heating does occur.

•Consider resizing a silo and subsequent feedout face for the time of year a silage will be fed out. Feed from larger feedout face areas in cold weather months. Feed from smaller feedout face areas in warm weather months.

#8 Excessive surface-spoiled silage in sealed bunker silos and drive-over piles


•Achieve a uniform packing density (minimum of 12 to 13 pounds of DM per cubic foot) within the top 3 feet of the silage surface.

•Shape all surfaces so water drains off the bunker or pile, and the back, front and side slopes should not exceed a 3-to-1 slope.

•Seal the forage surface immediately after filling is finished.

•Two sheets of polyethylene or a single sheet of OB film is preferred to a single sheet of plastic.

•Overlap the sheets that cover the forage surface by a minimum of 3 to 4 feet.

•Arrange plastic sheets so runoff water does not contact the silage.

• Sheets should reach 4 to 6 feet off the forage surface around the perimeter of a drive-over pile.

•Put uniform weight on the sheets over the entire surface of a bunker or pile, and double the weight placed on the overlapping sheets.

Bias-ply truck sidewall disks are the most common alternative to full-casing tires. Sandbags filled with pea gravel are an effective way to anchor the overlapping sheets, and sandbags provide a heavy, uniform weight at the interface of the sheets and bunker wall.

Sidewall disks and sandbags can be stacked, and if placed on pallets, they can be moved easily and lifted to the top of a bunker wall when the silo is being sealed and lifted to the top of the feedout face when the cover is removed. A 6- to 12-inch layer of sand or soil or sandbags is an effective way to anchor sheets around the perimeter of drive-over piles.

•Prevent damage to the sheet or film during the entire storage period. Mow the area surrounding a bunker or pile and put up temporary fencing as safeguards against domesticated and wild animals. Develop a rodent control program for the farm. Use a mesh or resistant secondary cover to exclude birds. Store waste polyethylene and cover weighting materials so it does not harbor vermin.

Regular inspection and repair is recommended because extensive spoilage can develop quickly if air and water penetrate the silage mass.

•Discard all surface-spoiled silage because it has a significant negative effect on DM intake and nutrient digestibility.

•Full-casing discarded tires were the standard for many years to anchor polyethylene sheets on bunker silos. These waste tires are cumbersome to handle, messy and standing water in full-casing tires can help spread the West Nile virus.

Poorly managed bagged silage

The bag silo has become a popular storage system on many farms in the United States. While bagged silage requires specialized equipment, bagging machines can be rented, or many silage custom operations provide them. Bags are also used to store extra silage when forage yields exceed the capacity of existing silo structures. Nevertheless, bagged silage is not trouble-free. The authors surveyed 16 nutritionists, dairy producers, silage contractors, university researchers and extension specialists and asked, “Bagged silage: What is important?” Selected responses are presented here.

•Bags should be located on a well-drained, firm surface, preferably on concrete or asphalt. Keep bags out of the mud, and provide feeders easy access to all bags.

•Low silage DM densities are a problem in bags. A skilled bagging machine operator is essential to insure a consistent, uniform fill and achieve an acceptable density.

•Mark (paint) bags with a number, date, crop, farm or field and use description (which cattle to feed).

•Record the DM content of all forage going into a bag, especially field-wilted, hay-crop silage, and mark the location of potentially problematic silage (too wet, too dry, too mature, etc.).

•Do not bag alfalfa too wet. The DM target should always be 35 to 45 percent.

•Check all bags at least three times per week, and mend or patch the punctures and holes.

•The silage removal rate at feedout must be sufficient to prevent the exposed silage from heating and spoiling, especially if multiple bags are open at the same time. Remove only enough plastic for silage needed daily.

Achieving a higher silage DM density: A case study dairy

A high DM density in the ensiled forage is important. Why? First, density determines the porosity of the silage, which affects the rate at which air can enter the silage mass during the feedout phase. Second, achieving a higher density increases the storage capacity of a silo. Thus, a higher DM density typically decreases the annual storage cost per ton of crop by both increasing the amount of crop entering the silo and decreasing ‘forage in’ versus ‘silage out’ losses.

Actual 2003 drive-over pile of corn silage on our case study dairy had a DM density of 11.5 pounds per cubic foot and an estimated silage DM recovery of 77.5 percent (i.e., a 22.5 percent ‘shrink’ loss).

The following changes were made for the 2004 corn silage :

1. The maximum pile height was lowered from 16 to 14 feet.

2. The forage delivery rate increased from 75 to 90 tons per hour.

3. The average forage DM content increased from 32 to 34 percent.

4. A second tractor was added to assist in packing.

5. The estimated forage layer thickness decreased from 8 to 5 inches.

These changes resulted in a predicted silage DM density of 15.8 pounds per cubic foot and an estimated silage DM recovery of 85 percent (i.e., a 15 percent ‘shrink’ loss) for the 2004 silage.  PD

References omitted but are available upon request at

—Excerpts from 2006 Penn State Dairy Cattle Nutrition Workshop Proceedings

See more articles like this at