Bunk and Silo Management By: Adam Parker


Farmers go through an enormous amount of work to have healthy, highly productive livestock and high yielding and high quality crops on their farms. What can often be overlooked is the middle step where we store and prepare the feed that we make for our livestock. Ensuring proper storage of your silage can allow for higher productivity, less losses from spoilage and overall a higher return on your investment on your farm.

From the beginning, moisture content at harvest can have a tremendous impact on the quality of you silage and how well it stores. If it is too wet it may seep and loose nutrients and if it is to dry it will not pack well and can have spoilage. More so in tower silos than horizontal bunkers, the weight of the silage itself is what compacts the silage to eliminate as much oxygen as possible. If the silage is to dry it becomes ‘fluffy’ and does not pack well. Matching the moisture content of your feed to your silo size and type will help you achieve better quality silage. See Table 2 and Table 5 for ideal moisture contents:

Packing density is important to help eliminate the air content in the silage pile to prevent spoilage and encourage faster fermentation. Again for tower silos this strictly comes down to matching the moisture content of the silage to the size of silo you have. For horizontal bunker silos there are more aspects to consider than just silage moisture content. With modern equipment today it is possible to pack silage very densely with large tractors.  The target density that many studies have concluded suggest having 44-48lbs of fresh silage per cubic foot. To properly pack a silage bunk progressing in a progressive wedge shape is suggested with each sequential layers being approximately 6” in depth. It is important to match the packing capacity of the packing tractor to that of the harvester. It would be impractical to slow the harvester down so including a second tractor in the bunker silo may be required to obtain enough packing between layers. Tractors with duals help to increase the packing area of the tractor but also distribute the weight of the tractor more. Therefore using additional ballast on the packing tractors is often suggested. Each 6” layer of silage should have uniform packing and should be driven over twice before the next layer of silage is added.

Horizontal Bunk Filling- Progressive Wedge is preferred:

Source: Qualitysilage.com

Packing a Horizontal Bunker Silo:

Source: https://www.americandairymen.com/articles/silostop-stresses-silage-safety

For every other day of the year there are some key management strategies to target. For tower silos feeding rate should be at least 2-3 inches of silage per day in the winter and 4-6 inches of silage in the summer to keep the silage fresh that you are feeding to you livestock. For horizontal bunkers the feeding rate off of the face of the bunker should be at least 4-6 inches in the winter and 6-8 inches in the summer. Matching your bunk face area to your feeding rate is key to keeping the silage fresh. If your bunk face is too large consider not piling as high and extending the length of the bunk to accommodate the volume of storage you need.   An example would be for 100 cows that get fed 40lbs of corn silage a day and the farmer has a bunk that is 25ft wide:

100 cows x 40 lbs/ day = 4000lbs of silage needed

Bunker density of 45lbs/ft2:  4000lbs/45lbs/ft2 = 89ft2 of silage needed

At an average feeding rate of 6’’ per day the bunk should only have: 89ft2/0.5ft= 178ft2 of face

To determine how high to pile his bunk: 178ft2 / 25ft wide = 7ft high silage pile.

Therefore if the bunk is piled any higher than 7 feet the farmer will struggle to maintain his goal of feeding 6 inches of silage off the face per day. It is important to do some rough calculations on you own farm to see if some minor adjustments might help your feeding rate on your farm. Obviously the infrastructure on your farm is likely concrete and not easily renovated or changed. If you are not capable of changing the size of the face of your bunk because of volume, physical or financial constraints; there are defacing attachments that might help improve the face of the bunk while at a slower feeding rate. These defacers tend to reduce the amount of exposed area and keep the face of the bunk more firm to prevent air from penetrating the face.  If a farmer uses a loader bucket and ‘digs’ into the pile to get feed, this often loosens the pile more than just the feed that is being fed that day. If you have a slow feeding rate this would be a concern however if you have a fast feeding rate it is likely less of an issue. It is recommended that you only loosen the amount of silage that you need on a daily basis and feed immediately. Loose silage that has been removed from the packed silage pile will spoil rapidly and therefore should be kept to a minimum.

Sealing silos is very important for both tower silos and bunker silos. It is suggested to inspect tower silo doors, walls and seems annually to make sure that they are air tight. Any leaks allow for additional spoilage and poorer feed. Bunker silos are recommended to be rounded on top to shed water and covered with at least one layer of plastic that is 6-8 mil in thickness. Some farmers will cover the walls prior to filling and then neatly cover and overlay the top plastic to shed water and become air tight.

In summary, diligent management of your silage storage and feeding is key to producing consistent top quality feed for your livestock operation. Planning ahead, silo face management, feeding rate, proper packing and sealing are all important considerations on your farm.

Capacity of Horizontal Bunker Silos:

Source: www2.gov.bc.ca/assets/gov/farming-natural-resources-and-industry/agriculture

Table 4: Capacity of Tower Silos:

Diameter and
Settled Depth
Alfalfa Silage (Tons) Corn Silage (Tons)
Moisture Content Moisture Content
40% 50% 60% 70% 40% 50% 60% 70%
18 x 50 157 196 260 370 210 240 270 320
18 x 60 194 240 320 460 260 290 340 390
18 x 70 230 290 390 560 310 350 400 460
20 x 60 250 310 410 590 330 370 420 490
20 x 70 300 370 490 700 390 440 500 580
20 x 80 350 430 580 820 460 510 580 670
24 x 60 370 470 620 880 490 540 620 710
24 x 70 450 560 740 1050 580 650 740 850
24 x 80 530 660 870 1230 680 760 850 980
24 x 90 610 750 1000 1410 780 860 970 1110

Source: J.C. Jofriet, University of Guelph, Guelph, Ontario.

Moisture content:

Rate per day of feeding:

Table 5. Ideal Moisture content of Silage given type of Storage:

Source: Omafra

Concrete/ Stave Tower Silo:

Source: OFA

Horizontal Bunker Silo:

Source: Hoards Dairyman
Silage Defacer:

Source: Western Producer

https://www.progressiveforage.com/forage-types/silage/packing-density-putting-dollars-to densitieshttps://fyi.extension.wisc.edu/forage/managing-forage-in-bunkersilos https://www.dairyherd.com/article/beyond-face-value-managing-silage-face