Bunker Silage Surface Spoilage
Dr. Ronald L. Boman
USU Extension Dairy Specialist
Last month at the Intermountain Nutrition Conference in Salt Lake City we were privileged to hear a presentation by Keith Bolsen from Kansas State University on �Managing Bunker, Trench and Drive-Over Silages for Optimum Nutritive Value.� Dr. Bolsen impressed us all with his recommendations on how to best manage bunker silos in the West. Besides harvesting the silage at the proper stage of maturity and moisture content, he put special emphasis on timely and adequate packing and then promptly covering the silo with plastic and weighting down the plastic with tires after filling. With today�s high capacity silage harvests we can easily overwhelm the people and the equipment packing the silage. In many cases, they aren�t allowed enough time to do a proper job of packing, and we end up with low density silage, which makes it difficult to establish and maintain anaerobic (absence of oxygen) conditions. This impedes the desired fermentation, causing a loss of dry matter, poorer quality silage and lower levels of lactic acid (which reduces the keeping qualities of the silage). I see too many corn silage and haylage bunker silos in Utah and the surrounding states that are left uncovered and have, especially in the case of corn silage, a 5 to 6-inch covering of black spoilage. This 5 to 6-inch black layer of spoilage represents as much a 1 to 2 feet of original silage material. This translates into a loss of up to 15 to 20% of the originally ensiled material. Apart from this loss, the nutritive value of the remaining silage is reduced (ADF and NDF values of the next 3-foot layer of silage can be 3 and 5 percentages units higher, respectively). Also the keeping quality of silage from uncovered bunker silos is markedly reduced during feed out. Just last month I saw corn silage being delivered to a large dairy from an uncovered bunker silo. The dairy receives the silage Monday, Wednesday and Friday and before it is all fed it begins to really heat up. The heated silage most likely has lowered levels of soluble carbohydrates and increased levels of ADF and NDF, and could reduce dry matter intake and even cause digestive disturbances. This heating could be minimized with proper packing, rapid and adequate covering (sealing), innoculating with lactic acid bacteria (Bolsen�s recommendation: �At the Silage harvester blower�). Research conducted by Dr. Bolsen with alfalfa silage shows dry matter losses in the top 3 feet of covered and uncovered bunker silos to be 8% and 46%, respectively. Other research from South Dakota with alfalfa silage indicated 16% dry matter losses for covered and 34% dry matter losses for uncovered bunker silos. Holstein heifers and steers fed the covered or uncovered alfalfa silages consumed an average of 12% less dry matter and gained an average of 42% less on the uncovered silage. According to Dr. Bolsen, (and I agree with him) there is really no substitute for 0.15 mm black plastic to cover bunker silos and tires to weight the plastic down. Besides these effects of dry matter loss and reduced forage quality by not properly covering the bunker silos, Dr. Bolsen maintains that feeding silage with spoilage (particularly Clostridial spoilage) reduces the �fiber mat or raft� in the rumen resulting in a strong tendency for the cows to come down with �LDA�s.�
(1) Bolsen, Keith K. 1003. �Managing Bunker, Trench, and Drive-Over Pile Silages for Optimum Nutritive Value: Four Important Practices.� Proceedings: 5th Intermountain Nutrition Conference, Salt Lake City, Utah, pp. 51-56.
(2) Bolsen, K.K., J.T. Dickerson, B.E. Brent, R.N. Sonon, Jr., B.S. Blake, C. Lin, and J.E. Boyer, Jr. 1993. �Rate and Extent of Top Spoilage Losses in Horizontal Silos.� J. Dairy Sci. 76:2940.
(3) McGuffey, R.K. and M.J. Owens. 1979. �Effect of Covering and Dry Matter on Preservation of Alfalfa in Bunker Silos.� J. Animal Sci. 49:298.
(4) 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.