Forages: Harvest and Storage

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Pub 811: Agronomy Guide > Forages > Harvest and Storage

Order OMAFRA Publication 811: Agronomy Guide for Field Crops


Pasture Management

A well-managed pasture will provide an abundance of low-cost forage for livestock. To harvest the optimum amount of forage and achieve the best livestock performance, use a rotational system. Ideally, a pasture will contain at least 35% legume in the forage being consumed by the livestock. Soil drainage and texture will influence the choice of forage species. Pastures with less than 35% legume content will benefit from the application of nitrogen at 50-75 kg/ha. Timing should coincide with good growing conditions and the need for more pasture. Use multiple applications if applying more than this rate.

Rotational Grazing

Spring turn-out of livestock should be timed according to the grass growth. Graze early species, such as orchard grass, early or growth will become too mature. Rotate the grazing fairly quickly. The faster the grass is growing, the quicker the rotation should be. With rotational grazing, it is important to gauge moving the livestock based on the last paddock planned for grazing in the rotation. In the early part of the growing season, a compete rotation may take 20 days. Late in the season, it may take 40 or more days for adequate re-growth and recovery before re-entry into a paddock.

Bloat Management on Pasture

Legumes can cause bloat of ruminant livestock. The younger the plants, the greater the risk. When grazing pasture that is greater than 50% legume, there are a number of steps that will reduce the risk of bloat:

  • Have the livestock full of forage when they enter the pasture.
  • Move livestock when the pasture is dry, not early in the morning with heavy dew or when wet with rain.
  • Offer dry stemmy hay to assist rumen stimulation.
  • Graze legumes when they're in bloom.
  • Consider using a feed additive.
  • Offer small areas at a time (equivalent to 1 day) to encourage the livestock to eat the stems as well as the bloat-causing leaves.

For more information on pasture management see OMAFRA Publication 19, Pasture Production.

Forage Quality

For forages that are harvested for storage, the type of livestock being fed determines the appropriate quality of forage. Match forage quality to the nutritional requirements of the animal. High-producing dairy cattle require quality feed that is high in digestible energy and protein. The benchmark alfalfa analysis for high-producing dairy cows is 20% crude protein (CP), 30% acid detergent fibre (ADF) and 40% neutral detergent fibre (NDF). For a beef cow, the most appropriate hay is more mature and higher yielding, and is therefore lower in protein and digestibility. Many recreational horse owners prefer hay that is more mature and contains more grass than is common in dairy hay. It is very important that it be entirely free of rain damage, mould and dust. Some markets also require hay to be green in appearance and entirely free of weeds. The remainder of this section will use the term "high nutrient quality" to mean high in protein and digestible energy.

Laboratory analyses of forages are essential for accurate ration formulation. The nutrient content of forages varies greatly depending on the type, stage of maturity at cutting and how well it is preserved.

See the OMAFRA Factsheet, Definition of Feed Manufacturing and Livestock Nutrition Terms, , for help with interpreting forage analyis reports.

Measuring Corn Silage Digestible Energy

Corn silage is unique since it consists of two very different components - high moisture grain and stover. High digestible energy is important to reduce the need for supplemental grain. Lower neutral detergent fibre (NDF) and increased digestible fibre (NDFd) are important for increasing intake, as well as energy.

Stage of Maturity Date % Digestibility % Crude Protein
Alfalfa Bromegrass Alfalfa Bromegrass
Medium bud June 4
Early flower (heads emerged) June 20
Full flower June 30
Early seed July 6

Digestible energy of corn silage is primarily determined by the relative amounts of starch and fibre (NDF) and their digestibilities. In the past, acid detergent fibre (ADF) was used to estimate energy, and NDF was used to estimate intake, but these measures alone do not consider digestibility. Newer methods more accurately estimate corn silage digestible energy using crude protein (CP), NDF, NDFd, starch, ash and fat. Starch digestibility can also be estimated using moisture, kernel processing scores and other laboratory starch digestibility tests.

Forage Harvest Timing

The timing of harvest is the most important consideration when trying to produce high-nutrient-quality forage. Forage crops decline in feeding value as they mature. Once alfalfa buds appear, feeding value declines about 0.2% per day in protein and about 0.4% per day in digestibility Table 3-10, Digestibility and Protein of Alfalfa and Bromegrass at Various Stages of Maturity. Short delays in cutting result in significantly lower forage nutrient quality. Of course, finding a window of dry weather can complicate things even further.

As a general rule of thumb, cut high-nutrient-quality, first-cut forage at the mid-bud to full-bud stage.

The timing of cutting is determined by the nutritional requirements of the livestock being fed. Cutting at the pre-bud or early-bud stage will result in reduced yields and may increase the risk of losing the stand. Extremely low fibre levels may result in nutritional problems. With grasses, a compromise between yield and quality occurs at "early head emergence from the boot." Orchardgrass will mature much earlier than timothy and bromegrass. Delayed harvesting of forage will give higher yields and greater plant persistence, but lower feed quality. With a large acreage of forage, it is advisable to start cutting earlier to ensure the later-cut material will still have adequate quality.

Subsequent second and third cuttings of alfalfa may be at intervals of approximately 30 days (mid-bud) to 40 days (early flower) or more, depending on whether the goal is high quality or maximum persistence and yield (see Forage Winterkill).

Predicting Alfalfa Quality in a Standing Crop

Methods being used to determine when to begin cutting first-cut alfalfa include:

  • the calendar date
  • stage of development (mid-bud, full-bud, etc)
  • growing degree days (GDDs) (see Growing Degree Days)
  • scissors cut
  • Predictive Equations for Alfalfa Quality (PEAQ)

Many producers base cutting decisions using NDF as the primary quality variable. For high-producing dairy cows, optimum alfalfa NDF for intake and dietary fibre is approximately 40%. With warm weather, NDF can increase about 0.7 units per day, and therefore quality can drop rapidly. NDF can vary from one year to the next by up to 10% when cutting is on the same date. The relationship between morphological stage, such as early- or late-bud stage, and NDF is not always high. Some laboratories offer scissor-cut analysis with a rapid turnaround time, in order to monitor forage quality in a standing crop.

The PEAQ method uses the longest stem and the most mature stems to estimate the NDF of the alfalfa in a standing crop. A PEAQ stick incorporates the NDF estimates onto an easy-to-read measuring stick, which can be used in the field. PEAQ is intended for use as a tool in making cutting decisions and is not meant to replace forage analysis and ration balancing. For details on how to use the PEAQ system, see Predicting Alfalfa Quality Using PEAQ on the OMAFRA website at

Dry Hay

The greatest amount of feed value is stored when both field and storage losses are minimized. The amount of each loss is largely determined by the moisture content of the forage when going into storage. Storing dry hay results in high field losses but relatively small storage losses. On the other hand, storing forages as haylage gives lower field losses but higher storage losses (see Figure 3-2, Estimated Hay and Haylage Harvest and Storage Losses).

Figure 3-2. Estimated Hay and Haylage Harvest and Storage Losses (Adapted from Hoglund, 1964)

Illustration of estimated hay and haylage harvest and storage losses.  The amount of each loss is largely determined by the moisture content of the forage.

Fast drying is a key to successful haymaking. In Ontario, good haymaking periods without rain can often be very narrow. There is a constant struggle between getting the hay dry enough to bale before the next rain, or baling before the hay is quite dry enough and getting mouldy, dusty hay. Conditioning and raking has to be balanced against excessive leaf loss.

Cutting and Conditioning

Disc mowers perform more dependably than sickle mowers in situations where forage is lodged, or in very thick grass stands. Disc mowers can operate at higher speeds and capacity but are more expensive.

Hay conditioners crush, crimp or flail the plant stems and speed up drying. Quicker drying reduces the risk of the hay being rained on and synchronizes the drying of leaves and stems, which can reduce leaf shatter. Grasses generally dry faster than legumes. Conditioners should be maintained and adjusted to ensure the optimal amount of conditioning. See the owner's manual.

Swath windrows should be left as wide as feasible after cutting in order to speed drying time and minimize respiration losses of soluble sugars. A wide swath decreases forage density and windrow humidity and increases the evaporative surface exposed to sunshine. Most mower-conditioners have an easy swath width adjustment.

Harvest Losses

There are a number of losses associated with the production of dry hay (less than 20% moisture). Since the leaves contain about half of the dry matter and two-thirds of the protein, leaf loss has significant impacts on yield and quality.

Table 3-11. Potential Haymaking Losses
Source of Loss % Loss of Dry Matter
Cutting and conditioning
Bailing small bales
Bailing large bales
Potential total loss

Even after cutting, forages continue to respire and consume sugars until the moisture content drops below 40%. Under relatively fast drying conditions, these losses can be kept to a minimum: 2%-8% of total dry matter. Under poor drying conditions (low temperature, high humidity, etc.), the plants take longer to dry down to 40% moisture, and dry matter losses as high as 16% have been measured.


Rainfall on windrowed hay sustains respiration and causes other losses. Nutrients such as simple sugars are leached from the leaves, and leaf loss increases, resulting in reduced digestibility. Sugars leached from the leaves results in less dilution and can increase the percent protein. However, the amount of protein produced per acre is reduced, and protein digestibility also decreases. Weathering also decreases the amount of hay the animals will eat, and rain damage increases the amount of mould on hay in the swath, which can make it less palatable and unsuitable for the horse market.

Mechanical Losses

As forages cure, the leaves and small stems become more brittle. Any mechanical operation, such as raking or tedding, done on material having less than 40% moisture causes leaf losses. Leaf losses increase as moisture content declines. If possible, rake when hay is moist. Leaf loss can be reduced by raking lower-moisture hay in the morning while dew is still present, slowing the speed of rotary rakes and turning a windrow with an invertor. Tedders are more commonly used on grass hay crops and can result in significant alfalfa leaf loss at lower moistures. Losses at the baler pick-up and in the baling chamber can be reduced by raking light windrows together at higher moisture and by traveling at maximum ground speed.

Potential Hay Harvesting Losses

The losses from haymaking that have been reported in research trials are summarized in Table 3-11, Potential Haymaking Losses.

Table 3-12. Storage Moisture Guidelines
Bale Type Storage Moisture (%)
Small square bales
Large round bales - soft core
Large round-bales - hard core
Large square bales

Storage Losses

Hay that is sufficiently dry and is stored under cover will normally experience minimal storage losses. These losses can usually be attributed to handling losses as the bales are moved.

Hay having high moisture is at risk from spoilage due to micro-organisms metabolizing sugars in the hay and giving off heat. The amount of potential damage to the hay is related to:

  • percentage of moisture in the hay
  • density of the bale and how tightly bales are packed in the mow
  • temperature and humidity of the outside air

Dry hay storage moistures guidelines for various bale types are outlined in Table 3-12, Storage Moisture Guidelines.

Storing bales inside or covering large bales dramatically reduces spoilage losses. In a 1.5-m (5-ft) round bale, 19% of the hay is in the outside 15 cm (6 in.), and 36% in the outside 30 cm (12 in.). Situate outside storage on a well-drained site. See the OMAFRA Factsheet, Big Bale Hay Storage, Order No. 88-052, or visit the website at

Feeding Losses

Feeding losses of dry hay can be quite significant. Feeding losses can be greater than 50% when hay is fed to cattle on the ground without a feeder. Cone and ring feeders have less waste than trailer or cradle feeders.

Hay Heating

The process of wet hay heating up and then burning is typically called spontaneous combustion. Spontaneous heating and combustion occur when sufficient moisture, oxygen and organic matter are present together to support the growth of bacteria and moulds. The reaction can be self-sustaining. The gases produced will ignite if they reach a high enough temperature. Care must be taken to ensure that hay is sufficiently dry to be baled and stored. Spontaneous combustion for hay usually occurs within the first 2 months of storage.

Usually, the first indication that the hay may be hot is the release of an odour similar to pipe tobacco and possibly steam rising from the mow. Mow temperatures can be monitored by pushing a pointed probe into the hay and then lowering a candy thermometer into it on a string. Never take temperatures alone, because fire pockets can develop, and there is a risk of falling in.

The following temperature guidelines can be used for monitoring hay mows:

  • 65°C - Entering the danger zone. Take temperatures daily.
  • 70°C - Danger! Inspect every 4 hours to see if the temperature is rising.
  • 80°C - Fire pockets may form. Call the fire department.
  • 100°C - Critical! In the presence of oxygen, ignition will take place.

If a thermometer is not available, an iron or copper rod pushed deep into the hay for about an hour will give an indication of the hay's temperature. If it is almost too hot to hold onto with bare hands once it is removed, there is a problem.

See the OMAFRA Factsheet, Silo and Hay Mow Fires on Your Farm, or visit the OMAFRA website at

Propionic Acid Hay Preservatives

The weather in Ontario makes it difficult to field-cure dry hay on a consistent basis. Propionic acid hay preservatives can help reduce the risks of heating, mould, spoilage and dry matter losses associated with baling hay at higher moisture.

Propionic acid is an organic acid that acts as a fungicide, inhibiting the growth of aerobic micro-organisms that can cause heating and moulding. The propionic acid inhibits mould growth while the bales "sweat' and "cure" down to safe moisture levels by dissipation and evaporation. Do not confuse proprionic acid hay preservatives with enzyme, bacterial inoculant or nutritive additive products, which differ in modes-of-action and effectiveness.

Propionic acid products are registered by the Canadian Food Inspection Agency (CFIA). Be sure to read the label, observe concentration rates and follow labelled application rates. Propionic acid hay preservative products now available are buffered to a pH of approximately 6.0 and do not irritate the skin and eyes as the older products did. They may also include acetic and citric acids, as well as a surfactant and colouring.

Hay treated with buffered propionic and other organic acid products is safe to feed to livestock. Propionic and acetic acids are organic acids that are also produced by microbes in the rumen (and the cecum and colon of horses) and then used by the animal as part of the digestion process.

Since the moisture content at baling determines the amount of preservative, it is important that moisture content be measured accurately. Hand-held moisture probes may not be accurate enough to fine tune the amount of preservative needed. There can be as much as 10%-15% moisture difference within a swath. This variation can lead to pockets of wet material that will be inadequately treated. To determine the range in moisture content, make a few bales and take samples from them rather than the swath. There is a difference between average moisture content and maximum moisture content. Adjust the rate to maximum rather than average moisture content.

Propionic acid is sprayed onto hay as it enters the baler. Basic systems include a tank, pump and nozzles. Automated computerized application systems are available that include in-chamber moisture sensors that automatically adjust application rates. These systems are virtually standard on large square balers.

For more information on preventing mouldy hay using propionic acid, visit the OMAFRA website at

Anhydrous Ammonia Treatment of Poor Quality Hay

Anhydrous ammonia is a preservative that will increase the crude protein content and digestibility of poor-quality hay. The recommended rate of application is 1% of dry hay weight, and the hay must be no wetter than 30% moisture. The hay should be covered with plastic to retain the ammonia, otherwise the preservative effect is only temporary.

As a preservative, anhydrous ammonia is not as good as propionic acid and should not be used on high-quality hay. Its use on high-quality hay has caused "crazy cow" syndrome where animals run wildly into obstacles, go into convulsions and possibly die. High-quality ammoniated hay should not be fed to animals with a high nutritional demand such as lactating cows.

Barn Hay Dryers

Barn hay drying systems are installed as a component in the production of quality hay. A properly managed hay-drying system reduces field curing time and the risk of losses due to rain, minimizes leaf loss and eliminates the danger of fire due to spontaneous combustion (see Hay Heating). A barn hay dryer makes use of a fan-and-air-duct distribution system to force outside air through partially dried hay placed in storage. This movement of air through the hay removes heat and excess moisture and will eventually complete the drying process that started in the field.

Horse Hay

The quality parameters for horse hay are different than for hay produced for cattle and sheep. Many horse owners determine the quality of hay primarily by its freedom from mould, dust and weeds, and a green colour. Hay that is not adequately dry at baling will mould, which results in dusty hay that causes respiratory problems. Horse hay should not have been rained upon. Most horses do not require hay with high protein content, and many recreational horses do not have high energy requirements. A timothy-alfalfa mix is common. Horse hay can often be harvested later in the haying season when the plants are more mature, giving some flexibility in haying and less chance of being rained upon. This will result in a higher yield of dry matter, but the hay will be lower in protein and energy.

There is often a market for horse hay in small square bales, as many horse owners do not have the equipment to handle large bales. There is also a growing market for horse hay in large square bales for both domestic and export markets. More information on horse hay is available on the OMAFRA website at

Haylage and Corn Silage

Storing forage as hay-crop silage, or "haylage," has advantages over storing it as hay. These advantages include:

  • lower harvest losses
  • lower labour costs because all operations can be mechanized
  • less dependence on good drying conditions, which allows the crop to be cut at the desired maturity

Corn silage is a popular forage crop due to yield, palatability, high-energy density and single harvest convenience.

Silage Crop Storage Types

The most common types of silage storage are:

  • vertical (tower) silos
  • conventional open top
  • oxygen limiting (sealed)
  • horizontal silos
  • bunker
  • piles
  • silage bags
  • large bale haylage (baleage)

When to Harvest Corn Silage

Harvesting corn silage at the correct moisture is critical for feed quality. The best livestock performance and corn silage fermentation usually occur when whole plant moisture is 65%-70%. This corresponds well to horizontal and bag silos, but silage may have to be somewhat drier in tower silos to prevent seepage. See Maintain Correct Moisture Content.

Kernel Milk Line

The kernel "milk line" has often been used to determine when to harvest corn silage, but this method has some limitations. The technique involves breaking a cob in half and looking at the kernels. After denting (0% milk line), a whitish line can be seen on the kernels. This line is where the solid and liquid parts of the kernel are separated while maturing and drying. This line will progress from the tip to the base. When it reaches the base (100% milk line), a black layer will occur. The traditional recommendation has been to harvest from one-half to two-thirds milk line.

There is considerable variation in the percentage kernel milk line and the moisture percentage of the whole plant. Whole plant moisture at one-half milk line may be too wet in some situations and much too dry in others. When the weather is relatively dry, the whole plant moisture may be lower than expected at any given milk line position. There are also hybrid differences in kernel milk line, due to the "stay-green" characteristic. A high stay-green rating means there is faster grain dry-down relative to stover dry-down. This is desirable in a grain hybrid, because as the grain dries, the stalk stays green and healthy, and broken stalks and lodging in late season are less likely. Many silage-only hybrids have a low stay-green rating, so the grain will have higher moisture relative to the whole plant. Lodging is less important in silage because of the earlier harvest, and having more moisture in the grain portion increases starch digestibility. Hybrids with high stay-green ratings may have milk lines that are more advanced relative to whole plant moistures. Silage-only hybrids that have lower stay-green ratings will be ready to harvest at a less advanced milk line. Check with your seed company representative for historic milk line recommendations for a given hybrid.

Measuring Percent Moisture

The most accurate method of determining when to harvest silage corn is to measure the moisture content.

  • Sample at least 10 plants from the field, avoiding the headlands. Watch for moisture variability within fields.
  • Chop a sample using a harvester or yard chipper. The finer the sample is chopped, the easier it will be to dry and the more accurate the result.
  • Use a commercial forage moisture tester, microwave or laboratory to determine the percentage of dry matter. Moisture testers and microwaves may not remove all the residual moisture in the sample and may underestimate moisture by about 3%.

Shortly after denting, when the milk line is about 20%, whole plant moisture can be determined. In a typical year, corn silage at this stage dries approximately 0.5% per day. Therefore, if the sample was 70% moisture, and 65% moisture is the target, harvest should be done about 10 days after the corn was sampled. In dry years, the drying rate will be more rapid; in wetter years, the drying rate will be slower. Moistures can be checked again closer to harvest if necessary.

Silage Fermentation

When forage is first 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 non-protein, nitrogen compounds. During this ensiling process, the acids lower the pH, while the production of ammonia tends to raise it. The production of ammonia increases the amount of time it takes to reach a stable pH.

In 2 or 3 weeks, the silage reaches a stable pH of 4.0-5.0, 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.

Silage Storage Losses

Most silage storage losses are associated with exposure to oxygen.

Respiration Losses

When plants are harvested and ensiled, the plant cell respiration continues, resulting in a breakdown of sugars and other carbohydrates.

Fermentation Losses

Primary and secondary fermentation result in varying amounts of fermentation losses. An extended period of fermentation can result in an excessive breakdown of sugars. Some types of bacteria are less efficient than others. At moistures over 70%, a clostridia fermentation can occur, which results in high levels of butyric acid.

Seepage Losses

When excessively wet material is put into a silo, the weight of the material can squeeze moisture from the silage at the bottom. The seepage carries sugars and other nutrients out of the silo. In addition, seepage can lead to excessive corrosion of the silo walls, reinforcing rods and result in the possible collapse of the silo. Silo seepage can also lead to fish kills if it enters a watercourse.


Heating causes plant sugars and proteins to combine and form indigestible compounds. This results in a "toasting" or browning of the silage and reduced protein digestibility. In extreme cases, because the silage is too dry or a continuous supply of air is getting into the silage, spontaneous combustion can lead to a fire. Such fires can happen at any time of the year and are almost impossible to extinguish.

Surface Spoilage

Less compacted, uncovered silage spoils because continuous exposure to oxygen results in the growth of aerobic micro-organisms (yeast, moulds and aerobic bacteria).

Feed-Out Losses

When a silo is opened to remove feed, there can be further losses in feed value. These losses are caused by moulds and yeast that become active in the silage when it is again exposed to oxygen. Secondary losses can occur at the cut face of the silage mass or in the bunk while being fed.

Recommended Silage Management Practices

Maintain Correct Moisture Content
  • conventional upright silos: 60%-65%
  • horizontal silos: 60%-70%
  • oxygen-limiting silos: 50%-60%
  • bag silos: 60%-70%
  • wrapped large bale haylage: 40%-60%.

Silage that is too dry will result in poor packing and air exclusion, poor fermentation and the production of heat. If haylage becomes too dry, cut fresh material and continue to fill the silo by alternating fresh and dry loads. The addition of water will not increase the moisture of dry silage. The water is not absorbed by the silage and can easily run off; a garden hose does not deliver enough water to make an appreciable difference in moisture content. Silage harvested at moisture percentages greater than 70% can result in seepage and an undesirable clostridia fermentation that results in butyric acid formation, high dry matter losses and poor feed quality, palatability and intake potential.

Use Proper Length-of-Cut

Fine chopping helps to exclude air by allowing tighter packing but must be compromised with rumen function requirements. The actual particle length will be different from the theoretical length-of-cut (TLC) and can be checked with a particle length separator.

With haylage, a 10-mm (7/16-in.) TLC is usually desirable. Low moisture silage may require a shorter TLC (6 mm or 1/4 in.) to ensure adequate packing. The length of cut is probably more critical with horizontal silos, although it is still important with upright and sealed silos. Harvester blades must be sharp and correctly set. Chopping finer than 6 mm (1/4 in.) is not recommended since it doesn't improve packing, requires more horsepower and may result in nutritional problems.

Corn silage "kernel processors" use rollers attached to the chopper to break cobs, crack kernels and shred stalks. The TLC recommended with processors is 19 mm (3/4 in.) rather than 10 mm (7/16 in.) without a processor. Processors may be more beneficial with relatively dry, hard-kernel, textured corn.

Fill Rapidly

Fill silos as quickly as possible to speed fermentation and minimize spoilage. If filling is delayed for a few days, the silage should be covered with plastic to reduce the chance of spoilage. In an upright silo, the silage is not compacted until a considerable depth of material has been put in the silo. The top part of the silage will be less dense and hold more air that could cause heating and loss of quality.

Pack Horizontal Silos Well

Bunk silos should be filled from back to front so that a "progressive wedge" shape is created, rather than filling from bottom to top. As the silo is filled, it should be packed in relatively thin layers (15 cm or 6 in.) to obtain good air exclusion. Sufficient tractor weight and packing time are critical. This may mean adding more packing tractors to increase packing time per tonne.

Maintain Tower Silos

A tower silo can act as a chimney. If air can get in, it will move up through the silage mass, which could lead to spoilage, heating of the silage and, in extreme cases, fire. Cracks in the silo walls or around the doors should be caulked or reconditioned to prevent the entry of air. Without good distribution, the lighter forage material will collect along the wall, leading to poor packing.

Seal Silos Well
  • Covering and sealing with UV-protected silage grade 6-mil plastic is essential in horizontal silos. The plastic should be held firmly in place. Old tires (split) placed closely together (touching) or other commercial products work very well. The plastic should not be allowed to flap in the wind, because it then acts as a bellows and pumps air into the silage rather than excluding it. Plastic should be placed so that rainfall runs off and away from the silage, rather than down the walls to collect at the bottom.
  • In conventional tower silos, forage at the top has low density that air can penetrate. To reduce spoilage until fermentation is complete, silage should be covered with plastic and weighted down by a few centimetres of silage. Take precautions to avoid silo gas. (See Silo Gas, opposite page.)
  • In sealed silos, the hatches should be closed at night and during interruptions in filling. When filling is complete, the hatches should be closed immediately.
Allow Complete Fermentation

Silage fermentation requires up to 21 days. To ensure silage stability and maximize feed bunk life, do not feed out of the silo until this process is complete.

Feed Out Quickly to Minimize Spoilage

The re-exposure of the silage to air at feed-out can result in the growth of moulds, yeast and aerobic bacteria. Slower feed-out rates increase the likelihood of aerobic spoilage. During hot, humid weather, larger feed-out rates are required to stay ahead of the spoilage. Size silos accordingly. Empty tower silos at a rate of at least 5 cm (2 in.) per day in winter and 7-10 cm (2 3/4-4 in.) per day in summer. Horizontal silos should be fed out at a minimum rate of 10-15 cm (4-6 in.) per day, depending on the season. Feeding mouldy silage is not recommended because it reduces intake and can cause nutritional problems.

Manage Silage Face to Minimize Spoilage

The silage face should remain tight and smooth to limit the penetration of air. Avoid fracturing the silo face by running at it with the front-end loader and using a lifting action. Minimize fracturing by scraping down the face with the front-end loader and allowing the silage to fall to the floor. Block cutters or shear buckets are other options. Uncover and loosen only as much silage as is required.

Silage Bacterial Inoculants

Silage inoculants are additives containing anaerobic lactic acid bacteria (LAB) that are used to manipulate and enhance fermentation in haylage (alfalfa, grass, cereal) and corn silage A more efficient fermentation resulting in more lactic acid and less acetic, propionic and butryric acids, is the desired result. The primary expected benefits are reduced fermentation losses (shrink) and often improved animal performance and feed efficiency. Bunk life may or may not be improved, depending on the pH and acetic acid levels.

The most common LAB in commercial inoculants are Lactobacillus plantarum, Enterococcus faecium, various Pediococcus species and other Lactobacillus species. Species and specific strains of LAB in commercial inoculants have been selected because they grow rapidly and efficiently, and produce primarily lactic acid. They increase the fermentation rate, causing a more rapid decline in pH, with a slightly lower final pH. The products of fermentation are shifted, resulting in more lactic acid and less acetic acid, ethanol and carbon dioxide. Lactic acid is stronger than acetic acid and contains almost as much energy as the original sugars.

If there is a high natural population of anaerobic bacteria, an inoculant is less likely to dominate the fermentation and provide a benefit. The natural population is increased by higher-than-average wilting temperatures, longer wilting times, rain during wilting and higher moisture contents during chopping. The application of a silage inoculant will not overcome the effects of poor silage management or poor weather conditions. These products are most effective when applied to high-quality forage under best management.

LAB inoculants are usually less beneficial in corn silage than in haylage. Corn silage is also more susceptible to secondary yeasts and moulds while being fed, resulting in shorter "bunk life." Lactic acid is preferred by yeasts when exposed to oxygen, whereas acetic acid can inhibit yeasts. For this reason, inoculants have been developed for corn silage and high moisture corn that contain Lactobacillus buchneri as well as LAB. Late in the fermentation, the L. buchneri utilize lactic acid to produce some acetic acid to reduce the growth of yeasts and spoilage at feedout.

Forage additives, including silage inoculants, must be registered with the Canadian Food Inspection Agency (CFIA) to be sold in Canada. To receive a "permanent" registration, companies must provide research that substantiates a nutritional label claim. Where research has been conducted but the results are not conclusive, products may be eligible to receive a "temporary" registration for up to 3 years to conduct additional research that substantiates a label claim. Temporary registration numbers start with a "T." Ask company representatives to provide independent research that substantiates their claims for the product. It is important that the product is labelled for the crop being ensiled, and that directions for storage and use are followed.

Table 3-13. Common Silage Problems and Causes
Hot or mouldy silage Low moisture content
Slow silo filling
Air leaks
Poor compaction
Slow feed-out
(dark, tobacco smell)
Heat damage caused by low moisture or poor compaction
Frozen silage Moisture too high
Poor fermentation
Vinegar odour Excess acetic acid caused by low plant sugars or poor fermentation
Seepage Moisture too high
Rancid odour Butyric acid from Clostridia fermentation caused by too high moisture
Alcohol odour Yeast fermentation from slow feed-out, oxygen or low-lactic-acid bacteria

Common Silage Problems and Causes

There are several common problems associated with silage. Table 3-13, Common Silage Problems and Causes, lists potential reasons for these problems. A fermentation profile analysis, which determines relative amounts of lactic acetic, butyric and proprionic acids, as well as ammonia content and pH of silage, can be used to diagnose suspected problems. A fermentation analysis reflects the quality of the ensiling process and can be used as an aid in improving future silage management practices.

Silo Gas

Nitrogen dioxide, NO2, is a dangerous chemical asphyxiant that is produced as a result of chemical reactions that take place almost immediately after plant material is placed into a silo. Even short-term human exposure can result in sudden death. It has a characteristic bleach-like odour and may be visible as a reddish-brown haze. It is heavier than air; therefore it will tend to be located just above the silage surface. It may also flow down silo chutes and into feed rooms.

Weather conditions and cultural practices will affect the amount of nitrates in plant material, which in turn will set the stage for the production of NO2 in the silo. For example, a dry period during the growing season followed by abundant rainfall will encourage a corn crop to take up high levels of dissolved nitrates. If the corn is harvested before the nitrates can be converted to proteins, nitrous oxide (N2O) and nitric oxide (NO) are produced. Unstable NO combines with oxygen to form deadly nitrogen dioxide.

When inhaled, NO2 dissolves in the moisture on the internal lung surface to produce a strong acid called nitric acid. Nitric acid burns the lung tissues, which is followed by massive bleeding and death. Repeated exposure to lower concentrations of NO2 will cause chronic respiratory problems, including shortness of breath, coughing and fluid in the lungs. Seek medical attention immediately upon exposure.

Silo Gas Precautions and Procedures

Post a "Silo Gas" warning sign in a visible location near the silo.

  • Do not allow children or visitors near the silo for 3 weeks after filling has been completed.
  • Contact your local fire department to determine if pressure-demand remote breathing apparatus is part of their emergency equipment. SCUBA equipment is not suitable, because the air tank is too big for climbing the silo chute or the outside ladder-cage.
  • Provide sufficient feed room ventilation to exhaust any silo gas that may have spilled from the silo.
  • During filling, adjust the distributor as needed to level silage. Do not level material by hand.
  • If it is necessary to enter the silo when filling is complete, do so immediately following the last load, on the same day. Leave the blower running while inside the silo.
  • Do not attempt silo entry without wearing a lifeline that is in the hands of sufficient outside help to pull you to safety.
  • If it becomes necessary to enter an oxygen-limiting silo, it is essential that an external air supply be worn.
  • A top unloader can usually ventilate a silo effectively. However, if it becomes necessary to service a defective unloader, assume that gases are present. To expel gases before entering, run the forage blower with the chute doors closed and the roof vent open. If the head space is greater than 5 m (16 ft), attach a tube adapter to the blower pipe. For a 7.2-m (24-ft) diameter silo with 5-10 m (16-33 ft) of head space, increase the ventilation time. Leave the forage blower running while in the silo.

See the OMAFRA Factsheet, Hazardous Gases on Agricultural Operations, or visit the website at

Large-Bale Haylage (Baleage)

Large-bale haylage, or "baleage," has become popular as an option for storing excellent-quality forage. By making large bales into haylage, a farmer can be more aggressive and consistent in cutting schedules as it reduces the weather risk factor. Some farmers use this as their main storage system, but it can also be a flexible second system of storage when silos are full and the weather doesn't permit drying. It produces a long-stem haylage. Plastic bagging or plastic wrapping is used.

The system makes use of equipment such as large round and square balers, which are readily available. Baleage may be fed using the same equipment as dry, large bales. This provides flexibility, to make as little or as much large bale silage as the weather dictates. Heavier equipment and four-wheel-drive tractors may be required when handling the heavier bales.

The cost and disposal of the plastic coverings have been major concerns. Cost is rationalized by considering the higher protein and energy value of the stored forage and the importance of the storage itself. Consider reduced harvesting losses and the higher quality of the whole forage crop as the harvest is moved ahead when determining the cost benefit of the system. See the OMAFRA Factsheet, Recycling Farm Plastic Films, Order No. 95-019, or visit the website at

With large-bale haylage, there is less or incomplete fermentation, resulting in a higher pH, or a less acidic environment, and a more unstable silage than conventional haylage. Greater emphasis must be put on good silage-making processes, especially the exclusion of oxygen. Adjust the length of storage time and how long the bales are exposed to oxygen before feed-out to weather conditions.

Successful use of baleage involves the following management practices:

  • Make firm, dense, uniform bales. Large squares are usually denser than rounds.
  • Bale at 40%-55% moisture. Lower moistures can work, particularly with large square bales wrapped with adequate plastic but are at a greater risk of spoilage.
  • Use enough plastic! Bales should be wrapped air-tight with a least 6 mils of plastic film (6 wraps of 1 mil or 4 wraps of 1.5 mil). To ensure against tears, 8 mils is preferable, particularly with drier baleage.
  • Wrap round bales within 2 hours of baling on hot days and within 4-12 hours at cooler temperatures. Large square bales are more forgiving of later wrapping.
  • Avoid using hay that was rained on.
  • Avoid raking to minimize contamination by Clostridia bacteria. Do not incorporate soil into the windrow with the rake.
  • Avoid fields where manure has been applied since the previous cut.
  • Avoid mature hay with low sugar content.
  • Be sure to repair all tears and holes in the plastic.

See Maintaining Quality in Large Bale Silage on the OMAFRA website.

For more information:
Toll Free: 1-877-424-1300
Author: OMAFRA Staff
Creation Date: 30 April 2009
Last Reviewed: 30 April 2009