Managing bunker, trench and drive-over pile silages for optimum nutritive value: four important practices
Published: February 20, 2007
By: KEITH K. BOLSEN - Animal Sciences Dept. of Kansas State University (Courtesy of Alltech Inc.)
When communication between the points of the triangle is ineffective, inefficiencies can result that directly affect the bottom line.
Although a dairy cattle 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 among the triangle’s three points.
The nutritionist’s major responsibility is generally to the dairy cattle 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 should moderate an annual meeting between the dairy manager, the forage crop grower, and the custom harvester. This can ensure that all involved understand and agree regarding expectations and implementation of the entire silage program. In other cases, a small dairy producer might be on the wrong end of a tight supply/demand situation and therefore lack the economic power to make demands on the crop grower and/or custom harvester. Then, the nutritionist must focus directly on the dairy producer, and make sure that the things directly under the producer’s control are done correctly. This paper focuses on four important silage management practices that are in the control of 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 spoiled silage.
Achieve 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.
In a recent study, 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 as well as 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 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/ hr on a fresh basis). Packing times were consistently less than 1 min/ton (on a fresh basis) at delivery rates above 60 tons/hr.
Table 2. Summary of core sample analyses from the bunker silos.
FACTORS CONTROLLING SILAGE DENSITY
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 driveover 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. However, if left unprotected, dry matter losses in the top 1-3 feet can exceed 60 to 70% (Bolsen et al., 1993). This is particularly disturbing when one considers that in the typical horizontal 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- 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 anchor it down with discarded tires (20-25 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 40 x 100-foot silo filled with corn silage can exceed $2,000. Loss from a 100 x 250-foot silo can exceed $10,000.
Manage the feedout face
The silage feedout face should be maintained as a smooth surface 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 of 6-12 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 spoiled silage
Sealing a silage mass using a polyethylene sheet anchored with tires is not 100% 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 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: (1) 100% normal, (2) 75% normal:25% spoiled; (3) 50% normal:50% spoiled, and (4) 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, neutral detergent fiber (NDF), and acid detergent fiber (ADF) digestibility (Table 3).
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 silagebased rations more than was expected.
Table 3. Effect of the level of spoiled silage on DM intake and nutrient digestibilities.
1The percent of the ‘slimy’ layer silage in the ration (DM basis).
a,b,cMeans within a row differ (P<.05).
References
Author: KEITH K. BOLSENBolsen, 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 S.M. Ocker. 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.
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. Report of Progress. 850:22-24.
Department of Animal Sciences and Industry, Kansas State University, Manhattan, KS, USA
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