How much silage is in the bunker?
Silage is usually stored in bunkers, drive-over piles or bags. Knowing the tonnage helps to plan rations, check that there is enough feed until the next harvest and set up the feed-out to limit spoilage.
The calculation
As-fed tonnage = length × width × average height × density
Usable dry matter = as-fed tonnage × dry matter % × (1 − losses)
Days of feed = usable dry matter ÷ (animals × dry matter eaten per animal per day)
For a pile with sloped sides, use the average height and width over the whole pile, or measure the cross-section at several points.
Example
A bunker 100 ft long, 20 ft wide, filled to an average 10 ft, packed at 44 lb per cubic foot as fed:
- volume: 20,000 ft³;
- as-fed weight: about 440 tons;
- at 35% dry matter with 10% losses: about 139 tons of usable dry matter;
- feeding 100 cows 22 lb of silage dry matter each per day: about 126 days.
Density matters
Well-packed corn silage reaches about 15 lb of dry matter per cubic foot (about 240 kg/m³), or 40 to 50 lb/ft³ as fed. Poor packing leaves air in the silage, which feeds the yeasts and molds that cause heating and spoilage. Use heavy tractors, thin layers of about 6 in and enough packing time for the delivery rate.
Feed-out rate
Once the bunker is opened, air enters the face. To limit heating, remove at least 6 in (15 cm) a day across the whole face, and about 12 in (30 cm) in warm weather. The calculator shows the daily advance from your herd’s needs. If it is too slow, a narrower bunker or a smaller face helps.
Typical losses
| Situation | Dry matter loss |
|---|---|
| Well-sealed bunker, fast feed-out | 8% to 12% |
| Average management | 15% to 20% |
| Uncovered pile | 25% or more |
Tips
- Cover the silage with oxygen-barrier film and tires or gravel bags within hours of filling.
- Measure the dry matter of the silage with a microwave or a Koster tester, or have it analyzed, rather than guessing.
- Keep walls and edges well packed, where most spoilage occurs.
- Recalculate the remaining stock every few weeks during the feeding season.