The Silage Triangle: Four Important Practices

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 This document is part of the Capturing Feed Grain & Forage Oppportunities - Proceedings from a Conference on Feeding, Growing & Selling series
Achieve a higher silage density | Protect silage from air and water | Manage the feedout face | Discard surface spoiled silage | References | Appendix

The points of the silage triangle are represented by persons responsible for (1) the animals, (2) the forage, and (3) the harvesting process. In some beef and dairy operations, one person is responsible for all three points. But in many instances, both growing the silage crop and harvesting and ensiling the crop are done completely on a contract basis, creating a situation where a different person is at each point of the triangle. When communication between the points of the triangle is ineffective, inefficiencies can result that directly affect the bottom line.

Although a livestock operation’s nutritionist - often an outside consultant - is not a direct part of the triangle, he or she has an obvious vested interest in how well the triangle performs. The nutritionist might be the key person in assuring effective communication between the triangle’s three points.

The nutritionist’s major responsibility is generally to the animal point of the triangle, so among his/her major responsibilities could be (1) educating the client about proper silage management, and (2) fostering communication. Ideally, the nutritionist might moderate an annual meeting between the livestock manager, the forage grower and the custom harvester, making sure that all involved are on the "same page" regarding expectations and implementation of the entire silage program.

In other cases, a small livestock producer might be on the wrong end of a tight supply/demand situation and therefore lack the economic power to make demands on the grower and/or harvester. Then, the nutritionist must focus directly on the producer, and make sure that the things directly under the producer’s control are done right. The producer probably has control over inoculating, packing, and sealing, and certainly has control over managing the feedout face and discarding spoiled silage.

This paper focuses on four important silage management practices that are in the control of beef and dairy producers and that are sometimes poorly implemented or overlooked entirely. These are: (1) achieving a high silage density, (2) effective sealing, (3) properly managing the feedout face, and (4) discarding surface spoiled silage.

Achieve a Higher Silage Density

First, density and crop dry matter (DM) content determine the porosity of the silage, which affects the rate at which air can enter the silage mass at the feedout face. Second, the higher the density, the greater the capacity of the silo. Thus, higher densities typically reduce the annual storage cost per ton of crop by both increasing the amount of crop entering the silo and reducing crop losses during storage. Recommendations have usually been to spread the chopped forage in thin layers and pack continuously with heavy, single-wheeled tractors. But the factors that affect silage density in a bunker, trench, or drive-over pile silo are not completely understood. Ruppel et al. (1995) measured the DM losses in alfalfa silage in bunker silos and developed an equation to relate these losses to the density of the ensiled forage (Table 1). They found that tractor weight and packing time per ton were important factors; however, the variability in density suggested there were other important factors not considered.

Table 1. Dry matter loss as influenced by silage density.

Muck and Holmes (1999) measured silage densities over a wide range of bunker silos in Wisconsin, and the densities were correlated with crop/forage characteristics and harvesting and filling practices. Samples were collected from 168 bunker silos and a questionnaire completed about how each bunker was filled. Four core samples were taken from each bunker feedout face and core depth, height of the core hole above the floor, and height of silage above the core hole were recorded. Density and particle size distribution were also measured.

The range of DM contents, densities, and average particle size observed in the hay crop and corn silages are shown in Table 2. As expected, the range in DM content was narrower for the corn silages compared to the hay crop silages. The average DM content of the corn silages was in the recommended range of 30-35%. But several of the haylages were too wet (less than 30% DM), which can lead to effluent loss and a clostridial fermentation, or too dry (more than 45% DM), which can lead to extensive heat damage, mold, and the risk of a fire. The average DM density for the hay crop and corn silages was similar and slightly higher than a commonly recommended minimum DM density of 14.0lbs/ft3. Some producers were achieving very high DM densities, while others were severely underpacking. One very practical issue was packing time relative to the chopped forage delivery rate to the bunker. Packing time per ton was highest (1 to 4 min/ton on a fresh basis) under low delivery rates (less than 30 tons/h on a fresh basis). Packing times were consistently less than 1 min/ton (on a fresh basis) at delivery rates above 60 tons/hour.

Table 2. Summary of core sample analysis from the bunker silos.

In a recent study, Muck et al.(2002) used a pilot-scale compactor to test the significance of five packing factors - tractor weight, packing time per as-fed ton, layer thickness, DM content, and silage height. - on density. A total of 48 trials were performed (17 with alfalfa, 3 with grass, 3 with alfalfa-grass mixtures, and 25 with corn). Pressure increased density, and the magnitude of the differences between pressures increased with each succeeding layer. Longer compaction times per layer also increased density, but the effect was not linear. Increasing compaction time per layer from 1 to 2 sec substantially increased density, but longer compaction times (5 to 10 sec) produced only small further increases in density. On several sets of trials, each layer was compressed for 6 sec, but the 6 sec was achieved in one of three manners: one 6-sec compression, two 3-sec compressions, or three 2-sec compressions. How the 6 sec of compression per layer was achieved had no consistent effect on density. Layer thickness had a smaller effect on density than expected from the bunker silo density survey.

For each trial, the increase in relaxed density with each succeeding layer fit a logarithmic equation well:
R = a + b 1n N

Where R is the dry matter density (kg DM/m3),a is a parameter reflecting the density of the first or uppermost compacted layer, b is a parameter reflecting the increase in density with an increasing number of layers, and N is the number of 30-cm layers. With hay crop forages, b was significantly affected by DM content and pressure whereas a was also affected by crop and chop length as determined by stepwise regression. Layer thickness and time were not significant. With corn, time and pressure affected both a and b. Additionally, processing affected a whereas layer thickness affected b.

These pilot-scale compactor results indicated that pressure, packing time, and layer thickness were important in determining density; and pressure appeared more important than the other two.

So what is the "bottom line" ? The correlations between density and a packing practice in these studies do not necessarily mean that a high density will be reached from a particular practice. However, there are several key factors that dairy producers can control to achieve higher densities, which will minimize DM and nutrient losses during ensiling, storage, and feedout.

Forage delivery rate - Reducing the delivery rate is somewhat difficult to accomplish, as very few dairy producers or silage contractors are inclined to slow the harvest rate so that additional packing can be accomplished.

Packing tractor weight - This can be increased by adding weight to the front of the tractor or 3-point hitch and filling the tires with water.

Number of tractors - Adding a second or third packing tractor as delivery rate increases can help keep packing time in the optimum range of 1 to 3 minutes per ton of fresh forage.

Forage layer thickness - Chopped forage should be spread in thin layers (6 to 12 inches). In a properly-packed bunker silo, the tires of the packing tractor should pass over the entire surface before the next forage layer is distributed.

Filling the silo to a greater depth - Greater silage depth increases density. But there are practical limits to the final forage depth in a bunker, trench, or drive-over pile. Safety of employees who operate packing tractors and who unload silage at the feedout face becomes a concern. Packing in bunkers that are filled beyond their capacity and the chance of an "avalanche" of silage from the feedout face pose serious risks.

Protect Silage from Air and Water

Until recently, most large bunker, trench, or drive-over pile silos were left unsealed. Why? Because producers viewed covering silos with plastic and tires to be awkward, cumbersome, and labor intensive. Many believed the silage saved was not worth the time and effort required. But if left unprotected, DM losses in the top 1 to 3 feet can exceed 60 to 70% (Bolsen et al., 1993). This is partic-ularly disturbing when one considers that in the typical "hori-zontal" silo, 15 to 25% of the silage might be within the top three feet. When the silo is opened, the spoilage is only apparent in the top 6 to 12 inches of silage, obscuring the fact that this area of spoiled silage represents substantially more silage as originally stored (Holthaus et al., 1995).

The most common sealing method is to place a polyethylene sheet (6 mil) over the ensiled forage and weight it down with discarded tires (approximately 20 to 25 tires per 100 ft2 of surface area). Dairy producers who do not seal need to take a second look at the economics of this highly troublesome "technology" before they reject it as unnecessary and uneconomical. The loss from a 40100-foot silo filled with corn silage can exceed $2,000. Loss from a 100 250-foot silo can exceed $10,000.

Manage the Feedout Face

The silage feedout "face" should be maintained as a smooth surface that is perpendicular to the floor and sides in bunker, trench, and drive-over pile silos. This will minimize the surface area exposed to air. The rate of feedout through the silage mass must be sufficient to prevent the exposed silage from heating and spoiling. An average removal rate 6 to 12 inches from the "face" per day is a common recommendation. However, during periods of warm, humid weather, a removal rate of 18 inches or more might be required to prevent aerobic spoilage, particularly for high-moisture (HM) ensiled grains and whole-plant corn, sorghum, and winter cereal silages. Hoffman and Ocker (1997) fed aerobically stable and unstable HM shelled corn to mid-lactation cows for three, 14-day periods. Milk yield of the cows fed the aerobically deteriorated HM corn declined by approximately 7 lbs per cow per day during each period compared to cows fed fresh, aerobically stable HM corn.

Discard Surface Spoiled Silage

Sealing a silage mass using a polyethylene sheet weighted with tires is not 100 percent effective. Aerobic spoilage occurs to some degree in virtually all sealed silos, and the discarding of surface spoilage is not always a common practice on the farm. But results of a recent study at Kansas State University (Table 3) showed that feeding surface spoilage had a significant negative impact on the nutritive value of a whole-plant corn silage-based ration (Whitlock et al., 2000).

The original top three feet of corn silage in a bunker silo was allowed to spoil, and it was fed to steers fitted with ruminal cannulas. The four experimental rations contained 90% silage and 10% supplement (on a DM basis), and the proportions of silage in the rations were: A) 100% normal, B) 75% normal:25% spoiled; C) 50% normal:50% spoiled, and D) 25% normal:75% spoiled.

The proportion of the original top 18-inch and bottom 18-inch spoilage layers in the composited surface-spoiled silage was 24 and 76%, respectively. The original top 18-inch layer was visually quite typical of an unsealed layer of silage that had undergone several months of exposure to air and rainfall. It had a foul odor, was black in color, and had a slimy, "mud-like" texture. Its extensive deterioration during storage was reflected in very high pH, ash, and fiber values. The original bottom 18-inch layer had an aroma and appearance usually associated with wet, high-acid corn silages, i.e., a bright yellow to orange color, a low pH, and a very strong acetic acid smell.

The addition of surface-spoiled silage had large negative associative effects on DM intake and organic matter (OM), neutral detergent fiber (NDF), and acid detergent fiber (ADF) digestibility. The first 25% increment of spoilage had the greatest negative impact. When the rumen contents were evacuated, the spoiled silage had also partially or totally destroyed the integrity of the forage mat in the rumen. The results clearly showed that surface spoilage reduced the nutritive value of corn silage-based rations more than was expected.

Table 3. Effect of the level of spoiled silage on DM intake and nutrient digestibility.


Bolsen, K. K., J. T. Dickerson, B. E. Brent, R. N. Sonon, Jr., B. S. Dalke, C. J. Lin, and J. E. Boyer, Jr. 1993. Rate and extent of top spoilage in horizontal silos. J. Dairy Sci. 76:2940-2962.
Hoffman, P.C. and Ocker, S.M. 1997. Quantification of milk yield losses associated with feeding aerobically unstable high moisture corn. J. Dairy Sci. 80(Suppl.1):234 (Abstr.).
Holthaus, D. L., M. A. Young, B. E. Brent, and K .K. Bolsen. 1995. Losses from top spoilage in horizontal silos. Kansas Agric. Exp. Sta. Rpt. of Prog. 727:59-62.
Muck, R. E. and B. J. Holmes. (1999) Factors affecting bunker silo densities. 1999. The XII International Silage Conference. Uppsala, Sweden. pp 278 - 279.
Muck, R. E., P. Savoie, and B. J. Holmes. 2003. Factors influencing density in bunker silos. U.S. Dairy Forage Research Center 2002 Research Report. pp 11-13.
Ruppel, K. A., R. E. Pitt, L. E. Chase, and D. M. Galton. 1995. Bunker silo management and its relationship to forage preservation on dairy farms. J. Dairy Sci.78:141-153.
Whitlock, L.A., T. Wistuba, M.K. Siefers, R.V. Pope, B.E. Brent, and K.K. Bolsen. 2000. Effect of level of surface-spoiled silage on the nutritive value of corn silage-based rations. Kansas Agric. Exp. Sta. Rpt. of Prog. 850:22-24.


(Note: for most problems, the solutions are the "opposite" of the causes.).

1. Excessive Effluent (i.e., seepage or run-off)

  • Ensiling forages too wet (i.e., low DM content) for the type and size of silo.
  • Weather did not allow the forage to be field-wilted properly before chopping.
  • Forage was not "conditioned" when it was cut.
  • Forage was placed in a window/swath that was too bulky for the time allowed for field-wilting.
  • The person(s) responsible for determining the DM content of the forage made a mistake.
  • Whole-plant corn, sorghum, or milk to dough stage cereals were harvested at an immature stage of growth.
  • The silage contractor arrived earlier than expected.
  • Chopping began earlier than optimum (i.e., because of the number of acres to be harvested).
  • Use weather forecasts when making forage management decisions.
  • Take advantage of new technologies in mowing, cutting, conditioning equipment.
  • Coordinate the merging of windows/swathes with the time of chopping.
  • Monitor the maturing/drying process of each field of corn, sorghum, or cereals so the harvesting time can be scheduled properly.
    Caution: Effluent has a very high biological oxygen demand (BOD). It should be contained near the silo of origin and not allowed to enter a nearby pond or water course.
2. Large Variations In The Dm Content And Nutritional Quality Of The Forage Ensiled.
  • Use multiple silos and smaller silos, which will allow better control of the forage inventory.
  • Put only one cutting and/or variety of “hay crop” forage in a silo.
  • Minimize the number of corn and/or sorghum hybrids in a silo.
  • Shorten the filling time of a silo, but do not compromise packing density.
3. Missing The Optimum Time To Make Corn Silage.
  • Warm, dry weather can speed the maturing process of the forage and grain components of the plant.
  • Wet fall weather can keep harvesting equipment out of the field.
  • Difficulty in scheduling the silage contractor.
  • Plant multiple corn hybrids that have different season lengths.
  • Better communication between the beef or dairy producer, crop grower, and silage contractor.
4. Excessive "Surface Spoilage" In Sealed Bunkers, Trench, And Drive-Over Pile Silos.
  • Achieve a high packing density in the forage that is within the top 3 feet of the silage surface.
  • Seal the silo as soon as possible after filling is completed.
  • Apply buffered propionic acid to the surface prior to sealing.
  • Apply sufficient, uniform weighting material to the polyethylene sheet.
    • Overlap the sheets by a minimum of three feet.
    • Use whole truck tires (i.e., that touch) to weight the overlap.
    • Whole tires are preferred over tire walls, and truck tire walls are preferred over car tire walls.
  • Prevent damage to the plastic sheet during the entire storage period.
5. High Concentrations Of Butyric Acid And Ammonia Nitrogen, Especially In "Hay Crop" Silage.
Note: these two components indicate that the forage underwent a clostridial fermentation.
  • Chop and ensile all forages at the correct DM content for the type and size of silo.
  • Pack properly to exclude as much air (oxygen) as possible, which will minimize the loss of sugars during the aerobic (respiration) phase.
  • Apply a homolactic bacterial inoculant to all forages to ensure an efficient conversion of plant sugars to lactic acid.
  • Avoid soil contamination while harvesting and ensiling.
6. High Concentrations Of Acetic Acid, Particularly On Wetter Corn And Sorghum Silages.
Note: Acetic acid indicates that the forage underwent a prolonged, heterolactic fermentation, and the silage has a strong "vinegar" smell.
  • Ensile all forages at the correct DM content.
  • Apply a homolactic inoculant to ensure an efficient conversion of plant sugars to lactic acid.
7. Heat-Damaged Silage.
Note: these silages have a dark brown to black color and a strong burnt carmel/tabacco smell.
  • Harvest at the correct stage of maturity (i.e., not too mature!).
  • Ensile forages at the correct DM content (i.e., not too dry!).
  • A high ambient temperature on the day of harvest.
  • Do not chop forage at a long particle size.
  • Achieve a uniform distribution of forage in the silo and a high packing density.
  • Avoid delayed filling of the silo.
8. Aerobically Deteriorating Silage During The Feedout Phase.
  • Harvest at the correct stage of maturity (i.e., not too mature!).
  • Ensile forages at the correct DM content (i.e., not too dry!).
  • Do not chop forage at a long particle size.
  • Achieve a high packing density.
  • Maintain a uniform and rapid progression through the silage during the feedout phase.
  • Avoid feeding from large silos during warm weather.
  • Do not leave silage-based ration is in the feed bunk for an extended period of time, particularly in warm weather.
Keith K. Bolsen
Professor Emeritus; Kansas State University, Manhattan, Kansas 66506
Adjunct Professor; Texas State University, San Marcos, Texas 78666
6106 Tasajillo Trail, Austin, Texas 78739
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This information published to the web on February 2, 2004.
Last Reviewed/Revised on July 22, 2015.