Harvesting and Storage
Corn should be harvested for silage at a moisture content that will
ensure good storage in the silo. Harvesting within the ranges shown in
table 3 will promote good packing and will minimize losses due to
heating or runoff. Silage ensiled too wet may ferment poorly and seep.
Seepage removes nutrients, particularly soluble nitrogen and
carbohydrates, and can damage the silo. Silage that is too dry will have
air pockets that prevent anaerobic fermentation and allow molds to
develop. In addition, the kernels become harder and less digestible. As
harvest is delayed from full dent to black layer (no milkline) crude
protein levels decline, fiber levels either remain constant or decline,
and digestibility remains relatively constant (table 4).
Table 3. Recommended moisture contents for corn silage stored in various
types of silos.
Recommended moisture content (%)
|Upright "oygen-limiting" silos
Table 4. Effect of harvest stage on yield and quality of corn silage.
Dry matter yield (T/A)
Crude protein (%)
|1 NDF = neutral detergent fiber
Source: Wiersma and Carter, University of
In dry, overmature corn silage the stove is less
digestible and contains lower amounts of
vitamins A and E. Often, adding water to a dry
forage becomes impractical because of the amount
of water needed. For example, using the equation
below, a 4000 lb load of silage at 45% dry
matter would require 137 gallons of water to get
it to 35% dry matter.
Amount of water needed to raise moisture content
of forage to 65% moisture (35% dry matter):
Gallons to add = ( [(FW x DM)Ã·FDM]- FW )/(8.33)
FW = forage weight in wagon
DM = dry matter of forage in wagon
FDM = desired final dry matter (e.g., 0.35)
Measuring moisture content with a microwave oven
To test the moisture content of corn silage with
a microwave oven, weigh out exactly 100 grams of
fresh silage on a paper plate (Donâ€™t forget to
adjust for the weight of the paper plate).
Spread the forage evenly on the plate and place
in a microwave oven. Heat on high for 4 minutes.
Remove the silage, weigh and record. Heat the
sample again on high for 1 minute. Weigh and
record. Repeat this procedure until the weight
remains the same. At this point, the weight in
grams represents the dry matter content of the
silage. To calculate the moisture content,
subtract the dry matter content from 100.
Example: After several heating cycles, the
sample weight stabilizes at 34 grams. Thus, the
dry matter is 34% and moisture is 66% (100-34).
Harvest timing can be estimated using the kernel
milkline (figure 4). When the milkline is Â½ to
2/3 of the way down the kernel, silage moisture
will often be in the range of 65%. Silage
moisture varies depending on region, growing
season, and hybrid so this technique should be
used only as a rough estimate of moisture
content. Whenever possible, measure the moisture
content with a commercial forage moisture tester
or in a microwave oven before harvesting.
Other considerations for timing the harvest of
corn silage are that as the corn plant matures,
the composition of the plant changes. More
mature corn silage will have more, drier grain
with harder seed coats, more starch and less
sugars, and less digestible fiber than earlier
harvested corn. Therefore, harvesting early will
yield more digestible stover and less starch
(from lower percentage of kernels), while
harvesting later (2/3 to Â¾ milk line with some
brown leaves) will mean about the same whole
plant digestibility but now the energy is coming
from an entirely different source (starch from
the kernels) that changes rumen dynamics. The
desired feeding program may influence the
maturity and storage facility you choose for you
corn silage (See â€œFeeding Silageâ€).
Harvest height is typically set at 4 inches.
Increasing the height to improve silage quality
is usually not profitable, since the improvement
in quality rarely offsets the yield loss. In a
Wisconsin study, increasing the harvest height
from 6 to 18 inches reduced yields up to 0.6
tons per acre while reducing the NDF from 59.9
to 59.4% (table 5). In another study, increasing
the harvest height to 6 to 8 inches may be
justified since nitrate levels are highest in
the lower portion of the stalk
Table 5. Effect of cutting height on yield and
forage quality of corn harvested at 75% silk.
||Cutting height (inches)
||Yield (T DM/A)
Abbreviations: DM =dry
matter, NDF = neutral detergent fiber, ADF =
acid detergent fiber, CP = crude protein.
University of Wisconsin, 1984.
Occasionally, corn is damaged or killed by frost before it reaches the desired maturity for ensiling. If the frost is early and green leaves remain on the plant, the crop will continue to accumulate dry matter and should be left in the field until it reaches the appropriate moisture content. Partially frosted corn often appears to be drier than unfrosted at the same moisture. If the plants are killed and still immature, they will likely contain too much moisture for immediate ensiling. Plants will dry slowly and dry matter losses will increase as the dead plants lose leaves in the field. The best strategy is to leave the crop in the field to dry down to an acceptable level unless dry matter losses become too high. When a crop that is ready to be ensiled is frosted, harvest it immediately. If the crop becomes too dry, consider a finer chop and adding water or a wet forage during silo filling. Harvesting losses will likely increase, but a reasonable quality silage can still be made.
When corn is so drought stressed that it may not resume growth, t should be ensiled. Corn in this condition usually has few ears and has leaves that have turned brown and are falling off. Be careful not to harvest prematurely because corn with ears and some green leaves may still be able to resume growth and accumulate dry matter later in the season. The net energy content of drought-damaged corn often is 85 to 100% of normal, and it sometimes contains slightly more crude protein. If drought stress is moderate, corn can often have higher than average energy in drought years because of a high grain content and high stover digestibility.
One concern with drought-stressed corn is the potential for high nitrate levels in the silage. High nitrate levels are found most frequently where high nitrogen rates were applied or when a drought-stressed crop is chopped within three days following a rain. Ensiling crops that are suspected to have high nitrate levels is preferred to green chopping since the fermentation process will decrease nitrate levels by about 50%. When in doubt, have the forage analyzed before feeding. High nitrate feedstuffs can be diluted by feeding with another feedstuff.
Drought can also affect the whole plant moisture content. When drought slows plant growth and delays maturity, the moisture content will be higher than suggested by the appearance of the crop. When a drought occurs at the end of the season, moisture levels may be lower than normal. Consequently, measuring the moisture content of drought-stressed corn before ensiling is recommended.
Corn plant residue following grain harvest can also be used as a forage. About 40 to 50% of the energy of the corn plant is in the leaves, stalks, cobs, and husk. Corn residue makes acceptable silage (stalklage) if moisture content is brought to about 65% by adding water or wet forages and if chopped between 1/8 and Â¼ inch theoretical length of cut which should be fine enough to pack tightly. Grain and protein supplementation is often required, which make the economics of feeding stalklage less attractive other than as a maintenance feed. For the highest quality stalklage, plan in the spring to harvest and handle high moisture corn, since the feed quality of stalklage declines as grain harvest is delayed. Also, less water will need to be added to silage at harvest. Hybrids vary in the feeding quality and moisture content of stover after grain harvest but there is little data available to compare hybrid. Holstein replacement heifer have shown adequate gains using stalklage as the forage in rations (table 6).
Table 6. Performance of replacement Holstein heifers fed a corn stalklage ration.
Dry Matter (%)
| Shelled corn
| Soybean meal
Average daily gain
(pounds per day)
(pounds dry matter fed per pound of gain)
(dollars per pound of gain)
NITRATES IN CORN SILAGE
High levels of nitrates in corn silage can be toxic to animals. The
level of nitrate in plant tissues varies greatly and depends on many
factors. Enzymes in plant leaves convert nitrates into protein. Nitrates
accumulate in the plant tissue during unfavorable conditions when growth is
slow and yet nitrates are plentiful. While nitrate accumulation in corn
silage is typically not a problem, itâ€™s important to understand the factors
that affect nitrate accumulation.
- Nitrogen availability. Nitrate content of corn
increases as nitrogen increases. Sources of nitrogen include
fertilizers, legumes, manure, and high soil organic matter
- Drought. Long, sustained droughts are not as likely
to cause accumulation of nitrates in corn as are brief, intense
droughts. Nitrate accumulation is highest after a drought-ending rain.
- Cloudy weather. Cloudy days often cause elevated
nitrate levels because the enzyme that converts nitrates to protein is
- Extremely high plant populations. Thick stands can
produce barren stalks which prevents movement of materials into kernels.
Nitrates accumulate in the stalk and leaves.
- Nutrient deficiencies. Deficiencies of nutrients
such as phosphorus, potassium, molybdenum, and manganese increase the
concentrations of nitrate. Root uptake of nitrate continues, but growth
is limited causing nitrates to accumulate.
- Plant age and plant part. Nitrates accumulate most
in the lower, older pars of plants. The stem and roots have higher
concentrations than the leaves and ears.
Fermentation in the silo will reduce nitrate levels by 30 to 50%. In
addition, a number of management options can be used to reduce or prevent
high nitrate levels in corn silage.
- Apply nitrogen at recommended rates. Be sure to subtract residual
soil nitrogen and manure applications from the total recommended amount.
- Minimize plant stresses due to nutrient imbalances, diseases,
insects, weeds, and insufficient moisture.
- Harvest on bright, sunny days.
- Dilute high nitrate corn silage with feed grains or legume hay.
Harvest and Storage
In well-planned operations, silo structure type I based on cost and
unloading considerations. Machinery for harvesting then should be sized
based on required fill rates of silos and on distance of fields from silos.
RATE OF FILLING
In general, the faster the silo is filled the better. Rapid filling (1)
minimizes the risk of feed losses due to inclement weather and advancing
maturity of the crop, (2) reduces labor and overall ensiling costs, and (3)
improves fermentation by minimizing exposure of the chopped forage to
oxygen. Slow filling encourages fungal growth which can result in unstable
silage at the time of feed out. When silage is stored in small-diameter
silage bags (8 ft), the rate of fill may range from 50 to 200 tons per day.
The filling rate of large-diameter silage bags (10 ft), and bunkers silos
(1000+ tons) can range from 100 tons to 500 tons per day.
The ideal capacity of field harvesting equipment ill depend on the acrege
or total tons of forage to harvest. In general, tractor-drawn forage
harvesters are used for silage capacities up to 2000 tons. Self-propelled
forage harvesters are more common when chopping more than 5000 tons of
Travel time is an important component of moving forage from the field to
the silo. Forage is generally moved with one of two types of wagons
(high-dump or self-unloading) or by truck. Self-unloading wagons require an
additional tractor or truck to move the forage from the field to the silo.
This type of system is typically used when hauling less than 2 miles.
Self-unloading wagons are required when using upright silos and certain
models of silage baggers. High-dump wagons and truck hauling are preferred
when forage must be transported farther than 2 miles. Large hydraulic
cylinders on the dump wagon raise the loaded wagon box and dump the forage
into a truck. This operation proceeds more quickly since the wagon does not
have to be disconnected from the tractor-chopper unit. A consideration with
the use of high-dump wagons is the need for an additional 20 hp of tractor
power to pull the wagon across average fields. Truck ca efficiently
transport forage over long distances and unload rapidly at the silo;
however, a greater capital investment is necessary. The purchase cost and
capacity of several harvest systems are show in figure 5.
FILLING AND PACKING EQUIPMENT
Once the forage arrives at the silo, it should be transferred and packed
quickly to exclude oxygen and promote the onset of fermentation. Forage
should be delivered to the silo daily until the silo is full. Delaying silo
filling over a weekend is strongly discourages as this will lead to
significant forage losses during ensiling and unstable silage at the time of
Techniques for packing vary depending on the silo type. Upright silos
rely on the weight of the silage to supply the packing pressure. Silage bags
require special bagging equipment that is adjusted to provide even tension
to form a firm tube of silage. Uneven tension results in loosely compacted
silage and inefficient use of the silage bag. When ensiling forage in bunker
silos, compact it in progressive wedges (figure 6) using a wheel tractor
with a front end loader or blade to move and pack silage. This technique
minimizes exposure of silage to air before covering. Crawler-type tractors
do not provide enough downward compaction pressure and are not recommended.
Tractor size should be dictated by the overall needs on the farm and size of
The amount of time spent compacting the silage affects fermentation.
Running the tractor across the surface many times leads to better
fermentation than when the forage is only leveled off with minimal
compaction. Ideally, allow 5 minutes packing time per ton of wet forage.
Troubleshooting silage harvester problems
|Poor or ragged cut stalks
Excessive cob lengths
|Dull knives, worn stationary knife, excessive
||Improper knife register on row crop unit; knives not centered on
|Lack of or spout blow
||Hole in spout liner; excessive blade to band
|Excessive power requirement
||Dull knives; dull or misaligned stationary
SELECTING A SILAGE STORAGE STRUCTURE
Major considerations in selecting a silo type
are speed of loading and unloading, volume of
storage needed, and structural cost. Other
considerations may include silo longevity,
initial investment cots, and potential to
purchase feed or share with a neighbor.
Characteristics of the major types of silage
storage structures currently used and their
costs are outlined in tables 7 and 8.
Table 7. Comparison of silo structure types.
|Silo structure type
||Holds large capacity
Can be filled with conventional farm
Requires less energy to move the
Offers faster unloading rates
|Requires greater care in filling and packing
||Smaller exposed surface area of silage
Requires less area for construction
Allows greater mechanization during
filling and feedout
Convenient to unload in winter
|High initial cost
Unloads more slowly
Silage cannot be stored at as high a
moisture content as for other silo types
Flexible storage system, allows you to increase capacity as needed
Low initial investment costs
|Bags must be protected to prevent rips
||Greatest loss of dry matter during
storage (up to 35% of the total forage
Large amount of exposed surface area
Difficult to pack
Table 8. Typical costs of various silage
per ton dry matter
Capacity dry matter(tons)
Useful lifea (years)
Average cost per yearc
Filled once ($)
Filled twice ($)
|20 x 50
|20 x 70
|25 x 88
|Concrete stave, oxygen-limiting
|16 x 60
|20 x 70
|30 x 80
|16 x 60
|20 x 72
|30 x 76
|16 x 60
|20 x 70
|30 x 80
|16 x 60
|20 x 70
|30 x 76
|20 x 80 x 10
|20 x 105 x 12
|50 x 150 x 12
|1 bag (8 x 150)
|2 bags (8 x 150)
|4 bags (8 x 150)
a Typical life depends on use as well as
structure type. Any life beyond 20 years
requires excellent management and care of the
b Includes cost of unloader in all cases, except
bunker and bagger which require a loader tractor
c Average annual use cost is based on zero
salvage value after a useful life of 20 years; a
10% interest rate on half of the initial cost;
typical costs for taxes (1.5%), insurance (2%
for tower silos), and repairs (2%) expressed as
a percentage of the initial cost.
d Bags cost %400 each, bagger costs $14,200.
e Cost of plastic to cover silage.
Source: Ishler et al., Pennsylvania State
Once youâ€™ve decided which type of silage
storage structure to purchase, youâ€™ll need to
determine where to place it. When evaluating
sites, look for places that are (1) convenient
for both loading and unloading, (2) in an area
where expansion is not limited, and (3)
positioned to collect effluent and avoid
Data presented in the appendix (figure 1 and
table 1) can be used to estimate the storage
capacities of silos of different types and
dimensions. The storage capacity of the bag
system is estimated at 1.2 tons of wet silage
per linear foot (10 ft diameter bag), 1 ton per
linear foot (9 ft diameter bag), and 0.8 ton per
linear foot (8 foot diameter bag) when forage is
ensiled at 40% dry matter. In addition, data are
available in appendix table 2 which account for
variation in the density of the silage stored in
bunker silos and its effect on silo capacity.
Good packing practices can substantially
increase the capacity of horizontal silos,
reducing the cost per ton of stored silage.
MINIMIZING SILAGE LOSSES
The most important practices for minimizing
silage losses are to
- Harvest at an appropriate dry matter,
- Fill the silo quickly with appropriate packing,
- Seal it well,
- Feed at an appropriate rate, and
- Maintain a firm silo face.
Dry matter loss during ensiling is an important
factor to consider when placing a value on the
cost of a selected storage system. Figure 7
illustrates typical storage dry matter losses
for various silo systems. The capacity of the
silo has a significant effect on dry matter
losses during storage feed out due to the
relationship of â€œexposedâ€ surface area to volume
(see figure 8)â€”the smaller the silo, the higher
Excess moisture content at harvest can cause
considerable loss of nutrients in effluent which
hurts the fermentation process and the nutritive
value of the silage. The minimum dry matter
content required to prevent effluent loss from
upright silos of different sizes vary depending
on the silo height and width (figure 9). If corn
silage is harvested and stored above 75%
moisture, dry matter losses during storage can
exceed 10 to 15%. The loss of effluent from corn
silage stored in bunker silos is minimal if the
moisture content is less than 75%. Absorbent
materials such as beet pulp and alfalfa hay
cubes can be added to wet silage at 5 to 15% of
the wet weight of silage or 50 to 150 pounds
(depending on moisture of silage) per ton to
eliminate loss of nutrients as effluent.
Covering and sealing forage can prevent
substantial losses of dry matter during ensiling
(see figure 10). In addition, the resulting
silage has a higher digestibility. It has been
estimated that covering a bunker silo with
plastic can return $8 for every dollar spent due
to reduced losses and increased animal
productivity. Use 4 mm plastic if storing
longer. Place 15 to 20 tires per 100 square feet
to hold down the plastic. The average losses of
dry matter associated with harvest, storage, and
feeding vary depending on moisture content
(table 9). Consideration of total losses can be
helpful when considering cropping decisions and
how much feed will need to be purchased
off-farm. The amount of field tonnage needed to
obtain 1 ton of feedable silage can be
calculated for different combinations of harvest
storage and feeding losses using the following
formula and number shown in table 9.
Tons to grow = (tons needed after
losses)/((1-HL/100) x (1-SL/100) x (1-FL/100))
HL = harvest loss, %
SL = storage loss, %
FL = feeding loss, %
Table 9. Expected dry matter losses in forage
harvest, storage, and feeding.1
Dry matter losses (%)2
||Tons to grow to
obtain 1 ton feedable silage
||Field tonnage to feeding
Considers dry matter losses only. Loss of quality was disregarded, but
could vary considerably
Chore Reduction for Confinement Stall Dairy Systems. Hoardâ€™s Dairy man,
Fort Atkinson, WI 1978, pp 12-13.
Source: University of Minnesota, 1980.
CALCULATING SILAGE USAGE
Determining silage dry matter intake of cattle
Example: You feed 100 cows 6 inches per day from a 20 x 60 ft upright
silo. The silo was filled initially and has 20 ft of silage remaining. The
depth of silage removed is 40 ft (60 ft â€“ 20 ft). Using appendix table 3,
there are 13 ton of dry matter in the next 4 feet. How much silage dry
matter intake will this provide?
Silage DM intake per cow (lb/day)=((tons of DM in next 4 ft)x (inches per
day fed))/((number of cows)) x 41.67
Silage DM intake per cow (lb/day)=(( 13 tons)x (6 inches per day
fed))/((100 cows)) x 41.67=32.5 lb/cow per day
Determining how many cattle you can feed
Example: You plan on feeding 35 lb/cow per day from a 20 x 60 ft upright
silo. The silo was filled initially and has 20 ft of silage remaining. You
need to remove 6 inches per day to prevent spoilage. The depth of silage
removes is 40 ft (60 â€“ 20 ft). Using appendix table 3, there are 13 tons of
dry matter in the next 4 feet. How many cows will this feed?
Number of cattle=((tons of DM in next 4 ft)x (inches per day
fed))/((silage DM intake per cow, lb per day)) x 41.67
Number of cattle=((13 tons)x (6 inches per day))/((32.5 lb per cow per
day)) x 41.67=100 cows
Determining silage dry matter intake of cattle
Example: You have 120 cows to feed. At 6 inches fed per day out of a 24
ft wide x 12 ft deep bunker, how much silage is each cow getting?
silage dry matter density is 14.4 lb/cu ft (â€œas isâ€ silage density from
appendix table 2 divided by silage dry matterâ€”36 lb/cu ft Ã· 40%).
Silage DM intake per cow (lb/day)=
((silo width,ft) x (silo vertical
depth,ft)x (inches per day fed))/((number of cows)) x ((DM density ))/12
Silage DM intake per cow (lb/day)=
((24 ft) x (12 ft) x (6 inches per day
fed))/((120)) x ((14.4 lb DM density per cu ft))/12=17.3 lb per cow per day
Determining how many cattle you can feed
Example: You decide to feed 15 lb of corn silage dry matter per cow each
day from a 24 ft wide, 12 ft deep bunker silo. How may cows do you need to
feed? Corn silage dry matter density is 14.4 lb/ cu ft (â€œas isâ€ silage
density from appendix table 2 divided by silage dry matter: 36 lb cu ft Ã·
Silage DM intake per cow (lb/day)= ((silo width,ft) x (silo vertical
depth,ft)x (6 inches per day fed))/((silage DM intake per cow,lb per day)) x
((DM density ))/12
Silage DM intake per cow (lb/day)= ((24 ft) x (12 ft)x (6 inches per day
fed))/((15 lb per cow,lb per day)) x ((14.4 lb DM per cu ft))/12=138 cows
At feed out, removing silage from the whole silo face at a rate of at
least 4 to 6 inches per day reduces losses due to poor aerobic stability.
Calculate the number of cows to feed or the amount of dry matter to feed per
day in order to use 6 inches of silage each day using the equations on page
20. Slow feedout rates allow more time for losses due to the growth of
yeasts, molds, and aerobic bacteria. This, in turn, decreases dry matter
intake. For example, when a corn silage that had been exposed for four days
was fed to dairy cows, their dry matter intake dropped 38% , from 60 lb to
37 lb per day. Feedout rate is a function of the number of animals being
fed. The amount of silage fed in the diet, and the silo design. Thus, silo
design and size should be matched with the feeding rate in order to minimize
silage losses during feedout.
Silo face management is also important in managing aerobic deterioration
in silage. Loose silage is more porous and allows greater air infiltration,
increasing the rate of aerobic growth. Figure 11 illustrates the dramatic
differences in dry matter losses associated with different levels of silo
face management. Maintaining a firm face and cleaning up loose silage that
has fallen to the floor of the silo on feedout will help minimize aerobic
Keeping an even, clean face on bunker silos is an important management
factor. To remove silage from a bunker, use the edge of the bucket on a
front-end loader to pull the silage down the face of the silo (figure 12).
Then scoop and load. This method will minimize infiltration of oxygen into
the silo face and eliminate loose and unpacked silage at the bunker floor.
Silage should never be scooped from the face as this allows more air to
enter, resulting in unnecessary spoilage.
Safety and Silage making
Silage making has the potential for causing serious accidents. As with
any operation involving large equipment, the key to safety begins with
prevention. This section describes the precautions to take to avoid injury
during harvesting and while working on or around silos.
Safety rules for all silage harvesting equipment and operations
- Properly maintain the equipment. Poorly maintained equipment will
not function properly, which increases the risk of an accident.
- Study the operatorâ€™s manual before each harvesting season,
especially the safety instructions.
- Make certain that all guards and shields are in place.
- Always turn off equipment before making any adjustments. Never try
to adjust or unclog a machine while its parts are in motion.
- Space tractor and equipment wheels as far apart as possible to
- Make certain the RPM of the tractorâ€™s PTO (540 or 1,000 RPM) match
the design RPM of the equipment.
- Inspect the field for stumps, stones, washouts, ditches, and other
obstacles which might damage the equipment or cause an overturn.
- Never permit riders
- Keep children, uninformed adults, and pets away from the machinery.
- Wear close-fitting clothes and sturdy slip-resistant work shoes
- Never operate equipment if you are ill, tired, or have alcohol or
medications in your system. You must stay alert.
Safety rules for working around silos
- Wear slip-resistant shoes; crepe or rubber soles are much safe than
leather or synthetic material soles.
- Always have one firm hand and foot hold.
- If you must do some work high up on a silo, wear a safety belt
secured to a rung of the ladder.
- Keep others away from the bottom of the ladder, should a tool or
part slip and fall.
- Do not climb a silo if afraid of heights
Silo ladders are perpendicular and the rungs do not provide the same foot
hold as a regular ladder set at an angle. Climb slowly with secure holds.
Practice descending from low levels. Many people find the descent from a
silo more difficult than the climbing.
During silo filling and for about 2 weeks after, take special care when
entering or working around a silo. Protect yourself and your livestock from
injury and death due to silo gas.
The fermentation of green plant material produces nitrogen dioxide (see
figure 13). After more oxidation and contact with waterâ€”such as the moisture
in the lungsâ€”nitrogen dioxide turns into highly corrosive nitric acid.
Low concentrations of nitrogen dioxide will cause a burning sensation in
the nose, throat, and chest. Heavy concentrations can cause death within
seconds. Even brief exposures to moderated concentrations can cause
extensive lung damage and pneumonia.
Carbon dioxide is produced in quantity in the silage fermentation
process. It is odorless, colorless, and tasteless and is 53% heavier than
air; thus, it also settles into low spots. It is not toxic, but it displaces
the air, lowers the oxygen level and causes a person to gasp for air and
become asphyxiated (death from a lack of oxygen).
Follow these precautions to reduce the danger of silo gas:
- Silo gas forms shortly after filling and persists for 2 to 3 weeks.
Stay clear of the silo for at least 3 weeks, and even after this time,
run the forage blower for 15 to 20 minutes with the door closest to the
top of the silo open before entering the silo.
- Beware of bleach-like odors or yellowish-brown fumes at the silo
base, the telltale signs of nitrogen dioxide.
- Ventilate silo feed rooms with open windows and fans during the
3-week danger period. Keep the door between the silo feed room and barn
closed tightly to protect livestock
- Properly adjust the distributor so that silage will be
well-distributed in the silo and will not require anyone entering the
silo during or after filling.
- Keep children and visitors away from the silo area during the danger
- If you should experience even slight throat irritation or coughing
around a silo, move into fresh air at once. See your doctor immediately
if you suspect youâ€™ve been exposed to nitrogen dioxide.
- If you must enter a silo during the 3-week danger period, wear and
approved, self-contained breathing apparatus and ventilate the silo for
20 minutes before entering. You should also be attached with a lifeline
to someone outside the silo.
A wide variety of silage additives are being marketed to improve corn
silage. The principal additives are (1) bacterial inoculants, (2) nonprotein
nitrogen sources such as anhydrous ammonia and urea, (3) enzymes, and (4)
organic acids such as propionic acid.
Each of these four major groups affects ensiling differently.
Consequently, knowledge of how these products work is an essential part of
determining which silage additive, if any, would be advantageous. Choice of
an additive should be based on meeting a particular goal or solving a
particular problem in ensiling as well as increasing profitability.
Additives should never be considered as substitutes for good silo management
but as tools for improving silage quality beyond that obtainable by good
The most common silage additive is the bacterial inoculants. Most
inoculants contain homofermentative lactic acid bacteria and supplement the
natural lactic acid bacteria on the crop to guarantee a fast and efficient
fermentation in the silo. Each product usually contains one or more strains,
usually of the following species: Lactobacillus plantarum, other
Lactobacillus species, Pediococcus species, or Streptococcus (or
Enterococcus) faecium. These bacteria grow rapidly under a wide variety of
conditions and produce mostly lactic acid when growing on the main sugars in
When the inoculant bacteria dominate the silage fermentation, they change
the end-products formed during ensiling. While naturally occurring lactic
acid bacteria produce acetic acid, alcohol, and carbon dioxide in addition
to lactic acid, inoculant bacteria produce a much greater proportion of
lactic acid. This shift in fermentation products lowers silage pH and
reduces dry matter loss during ensiling by approximately 2%.
Some inoculants can improve animal performance by increasing intake,
weight gain, milk production, and/ or feed efficiency. These improvements
are likely due to increased digestibility, but other factors may contribute
as well. Reduced levels of acetic acid and alcohol improve the palatability
of the silage and help improve microbial growth in the rumen. Inoculated
silage may also increase retention of dietary nitrogen in cattle.
These additives have had little effect on heating and spoilage of silage
at feedout (bunk life or aerobic stability), a common problem in corn
silage. Manufacturers are looking for microorganisms that will consistently
improve bunk life. Currently, however, you should not expect significant
improvements in bunk life from using an inoculant unless a manufacturer can
provide independent research data to verify such claims.
Inoculants are inexpensive, and consequently small gains in dry matter
recovery from the silo and small improvements in animal performance can
easily provide the financial incentive for their use. Unfortunately, these
products don't always work, particularly in corn silage. A recent survey of
research results found that inoculants affected fermentation approximately
40% of the time in corn silage in contrast to 70-75% in grass and legume
silages. And significant improvements of animal performance occurred only
20% of the time in corn silage. The poorer results with corn silage appear
to be due to higher natural levels of lactic acid bacteria on corn at
ensiling. When the natural population is much higher than the number of
bacteria supplied by the inoculant, it is more difficult for the inoculant
to dominate fermentation and improve silage quality. At the present time,
the factors affecting lactic acid bacteria numbers on corn at harvesting are
not known. Evidence suggests that populations increase on the plant as it
matures while freezing and thawing may reduce populations.
Inoculants vary in their effectiveness, so choose products with
independent research data to back their claims of lowered pH, increased dry
matter recovery, better aerobic stability, or improved animal performance.
Because of the high natural levels of lactic acid bacteria on corn, select
an inoculant that supplies at least 100,000 bacteria/g crop and has been
developed for use on corn. If possible, apply the inoculant at the forage
harvester to mix the product more thoroughly with the corn and give the
inoculant an early start.
Anhydrous ammonia is commonly used in making corn silage in some regions
of the United States. A more costly means of applying ammonia is through
aqua-ammonia. An alternative to ammonia is urea, which is not as popular and
is more expensive. The primary reasons for using these additives are to
increase the crude protein content of the silage and to increase silage bunk
life. The addition of ammonia immediately raises crop pH. Urea also
increases pH as urea is broken down to ammonia and carbon dioxide by plant
enzymes. Ammonia plus the high pH kill many of the yeasts, molds, and
bacteria that cause heating and spoilage. This should improve bunk life if
the silo remains well sealed prior to feeding.
Typically, these additives have little effect on the final pH in corn
silage because normally there are plenty of sugars for the lactic acid
bacteria to ferment. Because the crop starts out at a higher pH, ammonia
treatments increase both the total amount of acids produced and the amount
of acetic acid relative to lactic acid. These changes inhibit mold and yeast
growth. However, this shift in fermentation can decrease dry matter
Ammonia improves dry matter and fiber digestibilities by breaking down
hemicellulose and other components in plant cell walls. This should improve
animal performance but research trials have yielded mixed results. Research
with urea on corn silage has typically found small but consistent
improvements in weight gain, milk production, and feed efficiency compared
with silages supplemented with urea at feeding. Research trials with
anhydrous ammonia, however, have found results ranging from positive effects
on animal performance to a significant number of cases with negative
Typical application rates for either urea or anhydrous ammonia raise the
crude protein content of corn silage by 5 percentage points. This requires
varying amounts of additive depending on the moisture content of the silage.
For example, 6.5 lb/ton anhydrous ammonia is needed if the silage dry matter
is 33%, while approximately 8 lb/ton anhydrous ammonia is needed if the
silage dry matter is 40%. The decision to use urea or ammonia hinges on the
primary goal for using such an additive. If the primary objective is raising
the crude protein content of the silage, urea has a more consistent,
positive effect on animal performance. If reducing heating and spoilage is
the main objective, anhydrous ammonia is more effective. Precautions must be
taken to apply anhydrous ammonia safely.
Enzymes are one of the newest classes of silage additives. Enzymes reduce
fiber content by degrading cell walls and carbohydrates. These additives
usually contain a variety of enzymes including cellulases, hemicellulases,
pectinases, and amylases. Some inoculant products have enzymes included in
their formulation although enzyme concentrations in inoculant products are
often much lower than in straight enzyme products. Enzyme additives are
marketed primarily for hay crop silages with the goal of making a more
mature grass or legume silage feed like an immature one.
These products reduce fiber content in grass but are less effective in
legume silages. There is insufficient evidence to indicate their
effectiveness in corn silage. Enzymes work most effectively when the
moisture content is greater than 55%. The upper limit for moisture content
is determined by when seepage occurs in a particular silo type (see table
3). The reduction in fiber affects dry matter recovery either negatively or
positively depending on the moisture content of the crop. When the crop is
at or near a moisture content where seepage or effluent is produced, the
breakdown of fiber causes more seepage losses and reduces dry matter
recovery. In drier silages, the loss of fiber helps compress the crop which
reduces oxygen levels and increases dry matter recovery.
Despite the reduction in fiber content, improvements of animal
performance with straight enzyme products have been reported in only a small
percentage of research trials. The current enzyme products apparently
degrade fiber that is readily digested by ruminants. As these products
develop, improvements in animal performance should be seen.
Overall, enzymes currently do not appear to be a useful additive for
making corn silage. First, high fiber content is not usually a problem in
corn silage. Second, if corn silage is made at the appropriate moisture
range for enzymes, increased seepage losses are likely, especially in
upright silos. Finally, there appears to be little opportunity for recovery
of the additive's cost in corn silage.
PROPIONIC ACID MIXTURES
Propionic acid and mixtures of propionic acid with other acids such as
acetic are used to reduce spoilage and increase bunk life. Both propionic
and acetic acids inhibit the growth of yeasts and molds. Propionic acid is a
stronger inhibitor; however, it is considerably more expensive than acetic
acid. As a result, mixtures of the two acids help reduce the cost of the
These products may be added at ensiling, typically at rates of 0.2 to
1.0% of fresh weight. Do not apply these products at less than the
recommended rates as this reduces their effectiveness.
Often these additives are used when emptying a silo in situations where
the silage is heating in the silo and/ or in the feed bunk. In such cases,
the product is sprayed on the silage face. This will not prevent spoilage
losses in the silo during feedout, but it will reduce the rate of loss and
help keep the silage cooler in the feed bunk. When a silage is overheating
during feedout, it is also important to use it faster, if possible, to
Note: Web resources for Wisconsin are maintained by
Mike Rankin and
Forage. Please see
for an up-to-date listing.
Wisconsin Corn Silage Dry Down Results
county corn silage dry down programs. Sort by
county or region.
The Relationship between Corn
Grain Yield and Forage Yield: Effect of Moisture, Hybrid and Environment
by Dr. Joe Lauer,UWEX Agronomy Advice , December 2006
Calculating Grain Yield Utilizing a Corn Silage Forage
by Matt Lippert,
Wood County UW-Extension Agriculture Agent
Adjusting the Forage Harvester for Corn Silage Particle
Ron Schuler, UW Extension Ag Engineer
Crop Processor Adjustment for Corn Silage
Ron Schuler, UW Extension Ag Engineer
Crop Processing and Chop Length of Corn Silage: Effects
on Intake, Digestion, and Milk Production by Dairy Cows
by Dr. Randy Shaver, UW
Extension Dairy Scientist, et al.
Rehydration of Corn Forage Standing in the Field
Dr. Joe Lauer, Wisconsin Crop Manager Article, January,
Keys to Higher Corn Forage
by Joe Lauer,
UW Extension Corn Agronomist.
Uneven Maturity at Corn Harvest - Handling Silage and
by Dr. Joe Lauer,
Wisconsin Crop Manager Article, September, 2001
Estimating the Weight of Forage in a Forage Wagon
by Dan Wiersma, Marshfield
Ag Research Station. A "Focus on Forage" fact
On-farm Moisture Testing of Corn Silage
by Dr. John Peters,
Director- UW Soil and Forage Testing Lab, Marshfield Ag
Research Station. A "Focus on Forage" fact sheet
Predicting Corn Silage Harvest Dates
by Dr. Joe
Lauer, Wisconsin Crop Manager Article, August, 2000
Contract Feed Production Arrangements
by Joe Stellato, former Shawano
County Crops and Soils Agent
Working Successfully with a Custom Operator
Stellato, former Shawano Co. Crops and Soils Agent and
John Biese, former Outagamie
Co. Crops and Soils Agent
What Can We Learn From the Corn Forage Drydown During
by Dr. Joe
Lauer, Wisconsin Crop Manager Article, March 1999
Timing Corn Silage Harvesting and Custom Operators
Dr. Joe Lauer, Wisconsin Crop Manager Article, August
Corn Silage Yield and Quality Trade-Offs When Changing
by Dr. Joe
Lauer, UWEX Agronomy Advice, December, 1998
Kernel Milkline: How Should We Use It For Harvesting
by Dr. Joe Lauer,UWEX Agronomy Advice , April
Corn Harvest in Wisconsin During "Cool" Growing Seasons
Joe Lauer, Agronomy Advice Article, December 1996
Harvesting Silage at the Correct Moisture
by Dr. Joe
Lauer, Wisconsin Crop Manager Article, September 1996
Calculating the Value of Normal and Immature Corn Silage
by Dr. Joe
Lauer, Wisconsin Crop Manager Article, September 1996
Harvesting Spreadsheet - download as an Excel (*xls)
This spreadsheet, developed by Dr.
Gary Frank, allows you to help
determine your forage harvesting costs vs. custom