Don’t get robbed by hay and silage storage losses

Jared Goplen, University of Minnesota Extension educator – crops, and Nathan Drewitz, Extension educator

Taking precautions now can help minimize storage and feeding losses

A lot of time and energy is spent harvesting quality hay and silage. All of that can be wasted without proper storage. For hay and silage, up to 50% losses in dry matter can occur in some instances, which could be the equivalent of leaving half of your acres unharvested! Losses up to 20% can occur without even noticing. While hay storage losses are often related to moisture, silage losses are often due to exposure to oxygen during storage and feed out.

Taking precautions now can help minimize storage and feeding losses, helping your hard-earned forage supplies last longer.

Minimize silage losses



To minimize silage storage losses, limit the exposure of stored silage to oxygen. Oxygen allows microbes to metabolize dry matter and affect forage quality. Every effort to limit oxygen exposure will decrease losses and enhance quality and profitability:

  • Ensure proper moisture and packing density at harvest.
  • Exclude oxygen from storage structures.
  • Ensure adequate feed out rates and good silo face management to prevent spoilage at feed out.

Maintain tower silos and bunkers

Check and maintain walls, doors and ceilings of silos regularly to help minimize air exchange and keep precipitation from entering the silo through cracks in concrete and around doors. Spoilage in your silo that steadily worsens from year to year, especially around doors and walls, indicates that maintenance is needed. Even if cracks are not visible, silo maintenance may still be needed.

Maintain plastic

Silo bags, bunkers and piles all rely on plastic to exclude air and precipitation from the silage. Punctures in this plastic can be caused by people, animals, equipment and weather. Punctures will let air and water in, causing losses. To help prevent these losses, take the following measures:

  • Seal plastic coverings tightly to the silage surface.
  • Slope appropriately to drain water away from entry points into the silage.
  • Store silage bags away from areas that increase the likelihood of punctures.
  • Inspect bags and coverings periodically and repair holes with oxygen-excluding tape.

Proper Feed Out

Feed out loses can be as much as 15% depending on management and the storage structure used. To minimize losses at feed out, it is important to minimize air exposure and to feed out fast enough to keep fresh silage exposed. Losses can be minimized by feeding out 4” per day from tower silos, 6” per day from bunkers and piles, and 12” per day from silage bags. Silage with lower densities (<13 lb/ft3) will require faster feed out to minimize spoilage. Other proper feed out management practices to follow include:

  • Keep smooth, undisturbed surfaces exposed on silage piles and bags to minimize air exposure.
  • Roll back silage covers on bunkers and piles for no more than 3 days of feeding at a time and keep plastic sealed to the silage surface to avoid air penetration.
  • Avoid accumulated piles at the base of the feed out face as these piles will deteriorate faster.
  • Place silo bags, bunkers and piles on a surface that allows for effective feed removal without having to operate in muddy conditions.

Table 1. Estimated range of dry matter storage losses under “ideal” moisture conditions for different storage structures. Losses will be greater at higher or lower moisture contents than the optimum storage moisture. These estimated ranges include potential losses during filling, storage and feed out.

Silo type Moisture content
Dry matter loss
Upright silo 60-65 11-19
Oxygen-limiting silo 50-60 6-12
Trench or bunker (covered) 65-701 16-23
Silage bags 60-701 9-14
1Avoid ensiling hay crop above 70% moisture in structures to prevent clostridial fermentation.
Adapted from Holmes and Much, 2000. Preventing Silage Storage Losses.

Minimize hay losses

To minimize your hay storage losses, do everything you can to keep hay dry. Even small changes can have large impacts on hay storage losses, forage quality, and profitability:

  • Make dense bales of dry (<20%) hay (lower moisture for larger bales).
  • Stack hay so it does not trap moisture.
  • Improve drainage of your hay storage pad.
  • Consider buildings, tarps or bale wraps to keep hay covered.

Prevent moisture contact

Hay has the same enemy in the field as it does in storage — moisture. Preventing moisture contact with bales should be your top priority. Moisture enters hay from the top and bottom, coming from precipitation, as well as wicking from the soil. Keeping hay off of the ground and under a covering structure prevents the majority of moisture problems.

Hay properly stored should only lose 2-5% of dry matter over several years of storage. If hay gets wet, however, microbes come to life. Those microbes start eating away at the hay, which leads to losses in dry matter and deterioration in quality. The simultaneous loss of both dry matter and forage quality decreases hay value. In just 8 months, losses in forage quality can easily reduce hay value by more than $30 per ton.

Evaluate the ground where hay is stored

If you are storing hay on poorly drained soil such as sod or black soil, water will wick up from the ground. Hay that is dry at harvest can increase to over 30% moisture through wicking. This level of moisture can cause spoilage and dry matter losses over 20%, even over a short period of time. Losses may approach 50% if stored for more than one year.

  • Store hay on a well-drained surface such as gravel, rock, or old tires or pallets to keep hay out of contact with the soil to minimize dry matter losses to less than 15%.

Round vs. square bales

If hay must be stored outside, a number of small changes can minimize storage losses.

  • Square bales will be fine outside if bales are covered and elevated off the ground.
  • Tightly wrapped round bales are a better option when left uncovered, as they form a thatch layer and shed water best.
  • Net-wrapping improves the ability for round bales to shed moisture, resulting in 32% less dry matter losses compared to twine bales. If twine is used, spacing it less than 6 inches apart will improve the bale’s ability to shed water.

Bale size

Making larger bales means a greater percentage of the hay is protected inside the bale. The outer several inches of a bale tend to have the greatest spoilage, meaning larger bales help minimize storage losses outdoors.

  • The outer 2 inches of a 4- foot bale contains 16% of the bale’s dry matter, while just 11% of dry matter is contained in the outer 2 inches of a 6-foot bale.

Stacking method

Avoid stacking bales in an orientation that traps moisture between bales.

  • Uncovered bales should never be stacked in a pyramid, as this stacking method traps the most moisture and causes the largest dry matter losses.
  • End to end stacking, so bale ends are touching, is the best choice for outdoor bale storage. 3-5 feet should be left between rows of bales to allow water a place to go and air movement between the bales.
  • A north – south orientation of bales is best, as it permits more uniform sunlight to reach bales.

Cover bales to maintain quality

If you need to preserve high quality hay and have little tolerance for losses, consider covering bales stored outside. Depending on the quality of hay, it could be well-worth the hassle and extra work of covering hay outside with plastic or tarps.

  • Covering bales can reduce dry matter losses by an additional 6% or more compared to storing on a well-drained pad.
  • Consider a bale-covering technology such as bale sleeves or bale wraps, which can minimize losses so they are more similar to that of indoor storage.
  • Consider wrapping hay as baleage rather than storing as dry hay. Baleage can help minimize harvesting and storage losses.

Table 2. Effect of storage method on hay storage dry matter losses.



Hay storage method Dry matter loss range
Under roof 2-10
Plastic wrap, on ground 4-7
Bale sleeve, on ground 4-8
Covered, rock pad or elevated 2-17
Uncovered, rock pad or elevated 3-46
Uncovered, on ground, net wrap 6-25
Covered, on ground 4-46
Uncovered, on ground 5-61
From Craig Saxe, 2007, UW, Big Bale Storage Losses; how different options stack up.


  1. Impacts of a polyethylene silage pile underlay plastic with or without enhanced oxygen barrier (EOB) characteristics on preservation of whole crop maize silage, as well as a short investigation of peripheral deterioration on exposed silage faces
    Robinson, P.H., Swanepoel, N.
    Animal feed science and technology 2016 v.215 pp. 13-24
    plastic film, spoilage, surface area, corn silage, silage fermentation, air, polyethylene, oxygen
    Large silage piles, up to 15,000t, common in some dairy areas, present challenges since their large surface area creates an enhanced potential for oxygen to penetrate the mass. Use of thin inner (i.e., between the silage and main plastic cover) plastic films with enhanced oxygen barrier (EOB) properties are recognized by some governmental agencies as a mitigation of silage deterioration even though underlay films are generally accepted to only potentially impact the outer 30–50cm of the silage in a pile. In four large maize silage piles, underlay film with or without EOB properties had no impact on silage fermentation parameters indicative of spoilage in the outer 25.4cm of the silage pile, or in the 25.4–50.8cm depth below the surface of closed silage piles at ∼3 and at ∼6 months post pile building. In contrast, in a 5th pile, there was evidence of deterioration in the surface silage to a 25.4cm depth immediately behind the exposed silage face, which was not impacted by type of underlay film. A final experiment in a 6th pile showed that surface spoilage occurred well behind the exposed silage face, and that it moved into the pile at a similar rate as silage was removed from the face. Results do not support use of a thin plastic underlay film with EOB properties, versus one without, since air ingress to the silage mass through the silage pile cover appeared minimally causative of silage deterioration, which was associated with the exposed face. Maize silage deterioration of exposed face silage would likely be minimized by increasing speed of exposed face movement, and/or use of weight lines directly behind the exposed face, as has been recommended by others.

  2. Conclusion of Dr. Robinson’s paper is:

    One shows how the using a thin, clinging and conforming film under the thicker protective top layer reduces spoilage, the same as widely thought thin “enhanced 02”a barrier film does. The cling, not the barrier is why they both work. There are other reports that I can supply.

    The CLING, not the 02 barrier is what makes this practice (that started in Germany in 1979) Work…
    Taken together, results do not support use of a thin plastic underlay film with EOB properties, versus one without EOB properties in maize silage piles, at least if silage feed out is prior to ∼6 mo after pile building, since it seems that ingress of air to the silage mass through the plastic cover of the silage pile during this period is minimally, or not at all, causative to silage deterioration, which was only associated with the exposed silage face. Silage deterioration at the exposed face appears likely to be minimized by increasing the speed of exposed face movement over the ground, and/or use of movable weight lines directly behind the exposed face. However further research is required to investigate the interaction of these factors.

  3. One point that was not made perfectly clear is that using “enhanced 02” film is a total waste of money as proven by UC Davis study and “history”.. the cling and conforming effect of a thin film is what is causing the reduction of spoilage, not the barrier properties.. That is why increasing the 02 properties of the top, thick, non-conforming film did NOT work.

    Double Layer Covering History
    Good news
    In 1972, the German government mandated recycling of Ag plastic films, including silage coverings. Other countries soon followed. However plastic recyclers complained the silage cover plastics were “dirty” and would have very little, if any, recycle value.
    A solution was proposed: Use a two layer covering system with a bottom layer of thin, pliable, conforming, puncture resistant 1.6 mil polyethylene so the thicker top protective layer of film would stay cleaner and have a high recycle value. Simple!

    Better news
    When farmers used this 2-layer system they discovered silage spoilage was dramatically reduced compared to the one layer system they had been using. Since the thin inner film hugged the pile and conformed to its surface they called this type of film “Cling Film”, “Vacuum Film”, or “Underlay Film”. The best news was that the thin underlay was very inexpensive and the value of better silage far exceeded the cost. All film producers soon started supplying this type of film and it became standard throughout Europe and many other parts of the world, except in the USA.

    US news
    Around 2005 Dr. Brian Holmes and associates at the University of Wisconsin started testing a proposed very different 2-layer silage pile covering system. This “multi part system” used thin underlay film with “Enhanced Oxygen Barrier” properties (called “EOB” film) under standard 5 mil sheeting, with sandbags around the bunker perimeter and on top of overlaps, and sidewall sheeting extending 5’ out from the side of the bunker.

    The testing of the multi-part 2-layer “system” showed far less silage spoilage than the widely used 5 mil single layer system. However, it was not clear which part of the 2-layer multi part system was causing the improvement. Was it the enhanced barrier properties of the thin film, the other components of the “system” or was the improvement simply due to the presence of thin film in contact with the silage?

    To isolate the importance of the EOB variable, researchers then compared a single layer EOB 5 mil film against standard 5 mil single layer film and found no difference in silage quality. This finding called into question the importance of the EOB properties altogether.
    To restate
    • The research never proved the barrier properties of the “new system” were the cause of better silage.
    • The research did not compare the “new” 2-layer EOB “system” against the proven European “cling” system that used 2 layers of standard poly (5mil over 1.6).

    Conclusive news that answers the question
    Recently Dr. Peter Robinson of University of California at Davis completed a two-year study comparing a normal oxygen barrier 1.6 mil underlay film called Hitec Underlay, and a 1.8 mil enhanced oxygen barrier underlay called Silo Stop. Both underlays were placed beneath a standard 5 mil top layer. The only variable was the bottom layer film.
    For each test pile, the two underlays were placed on opposing sides of the pile and overlapped 5’ at the top. After 60’ along the length of the pile, the films switched sides. This eliminated factors caused by orientation to the sun.
    The test was done on 1 wheat pile and 4 corn silage piles, and confirmed that increasing the oxygen barrier properties of an underlay film made no difference to silage quality! Even the researchers were surprised with the outcome as logic would lead you to bet that an EOB film would for sure give better results, but in fact, it is not true.

    As they say in Europe, ‘The Cling is the Thing’. The thinner and clingier the bottom layer the better the results. Look for a product like the 21 year old original film that is thin and Saran-like so that it clings to the silage surface. Also, the underlay film should be applied loose to help it conform to the surface.

    To maintain quality feed it is a good practice to use moveable weight lines directly behind the exposed face to limit entry of air to the pile between the plastic cover and silage surface at the face.

    Even Better news

    Finally the U.S. dairy industry has access to a proven 2-layer silage covering system (black and white 5 mil top layer plus 1.6 mil bottom layer) that is eco-friendly, affordable, and will assist in financing U.S. recycling efforts.

    Farmers can now make more money by participating in plastic recycling! USA dairy farms using this inexpensive and environmentally friendly system can now separate the ‘dirty’ thin underlay from the clean 5 mil top layer. This allows 70% of the silage pile plastic covering to have much higher recycling value.

    In addition, normal underlay film with normal barrier properties is 100% recyclable unlike some EOB films that enhance barrier properties by using non-recyclable polyamide additives rather than recyclable EVOH.

    A simple solution where all sides win!

    Sometimes good intentions result in unexpected, and even better, consequences.

    For more information and UC Davis reports contact:

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