12/27/2019
Losses Associated with Splitting Bunker Silos
Shared from Inside the ZONE® newsletter, Pioneer Nutritional Sciences
Introduction
Some producers with large bunkers opt to split the bunker to either maintain access to fermented silage following silage harvest or to remove more silage per day from the face thus prevent spoiling and aerobically unstable silage. Figure 1 illustrates normal and thermal images of a well-managed, mechanically-faced bunker split down the middle due to excessive width making feed-out rate a concern. The reddish-white colors in the thermal image clearly indicates that oxygen is penetrating the exposed side resulting in microbial activity and nutrient loss.
Figure 1. Example of exposed sidewall from splitting a bunker.
A case study was conducted in Michigan to assess potential nutrient and economic losses from prolonged oxygen exposure on the silage sidewall.
Case Study Methodology
The well-compacted midwestern corn silage bunker used in this field trial is shown in Figure 2. The bunker was 12 feet high x 100 feet long. The producer made a new split every 4 weeks (or 13 times per year). The exposed silage sidewall (yellow arrow) had been exposed for 4 weeks.
Figure 2. Trial bunker with exposed silage sidewall.
The feeder removed and discarded the approximately 6 inches of obviously spoiled silage (Figure 3) before adding corn silage to the TMR mixer.
Figure 3. Visible spoilage layer.
Silage samples were analyzed at 6-inch intervals (Figure 4) from the long-exposed face.
Figure 4. Sampling locations on exposed face.
Trial Results
The impact on silage pH and volatile fatty acid (VFA) content at the various sampling depths (red numbers at top of chart) is presented in Figure 5. There was higher silage pH (red line) and lower lactic acid (green line, likely metabolized by yeast) nearer the exposed face.
Extended Exposure Silage Face
Inches inside silage from 4 wk exposed edge
Figure 5. Silage pH and VFA profile.
Nutrient analysis of the silage (Figure 6) at various depths (red numbers) show a 12-point lower NDFD (30-hour) and 13-point lower starch content closer to the exposed face. It also indicated an 8-point higher uNDF240 (blue line) which could limit dry matter intakes.
Extended Exposure Silage Face
Inches inside silage from 4 wk exposed edge
Figure 6. Silage pH nutrient analysis.
The dry matter density (Figure 7, blue line) was reduced from 21.8 lb/ft3 at 36-inches to around 20 lb/ft3 nearer the exposed face indicative of significant dry matter loss. The higher % dry matter (orange line) near the exposed face was an unexpected result. Respiration of the collected samples should not have been a significant source of error as samples were collected, kept cool, delivered and analyzed by a commercial laboratory within a matter of a few hours. It can only be theorized that the reduced density, even several inches into exposed side, permitted accelerated evaporation of silage moisture.
Extended Exposure Silage Face
Inches inside silage from 4 wk exposed edge
Figure 7. Silage dry matter and dry matter density.
Economic Analysis
An attempt at assigning the magnitude of potential economic loss splitting this bunker is shown below using corn grain as a nutritionally equivalent replacement for the loss dry matter given that starch content and fiber digestibility is lower while silage fiber content is further concentrated.
Spoilage (100% loss)
- 6” discarded daily by feeder = 0.5 cubic feet/ft2 of exposed face with assumed original density of ~20 lb/ft3 (since density is higher below but lower above test location, 20 is an estimate).
0.5 x 20 = 10 lb DM = 28.5 lb/ft3 as fed (35% DM) @ $42/T corn silage = $0.60/ft2 of exposed split face.
DM Loss
- 30 inches deep = 2.5 ft3 per ft2 of split exposed face @ average density loss of ~.75 lb DM/ft3 (reduced from 21.8 to 20.2 per trial data) = 1.88 lb DM loss/ft2 of exposed split face.
Value DM loss as replacement value with dry corn grain @ $4/bushel = $0.084/lb corn DM. $0.084/lb corn DM x 1.88 lb DM loss/ft2 of exposed split face = $0.16 DM loss/ft2 of exposed split face.
Given that this bunker was 12 feet high x 100 feet long (1200 ft2) the potential cost in terms of spoilage and DM loss was 1200 ft2 x $0.76 = $912 each time it was split. This operation made a new split every 4 weeks (13 times per year) so the total potential loss would be in the range of $11,856 annually ($912 x 13).
Conclusions and Potential Solutions
- Dry matter losses in split bunkers/piles occur well beyond visible spoilage; even in silages with high initial dry matter densities and low silage pH.
- In this case study, DM losses were incurred at least 36 inches into the exposed face within 4 weeks of being split. Forage nutrient density is also measurably reduced at least 36 inches into the exposed face.
- When bunkers are inoculated with products containing highly-research Lactobacillus buchneri strains (like found in Pioneer® brand 11C33), it is recommended to feed across the entire face, even if only removing 2-3 inches per day, rather than splitting the bunker and prolonging oxygen exposure on the exposed side. L. buchneri will inhibit yeast growth and help stop the cascade of events leading to spoilage, heating and dry matter loss.
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