|Pahlow, Guenter -|
Submitted to: International Silage Conference
Publication Type: Proceedings
Publication Acceptance Date: July 13, 2009
Publication Date: July 27, 2009
Citation: Pahlow, G., Muck, R.E. 2009. Managing for Improved Aerobic Stability. In: Broderick, G.A., Adesogan, A.T., Bocher, L.W., Bolsen, K.K., Contreras-Govea, F.E., Harrison, J.H., Muck, R.E., editors. XVth International Silage Conference Proceedings, July 27-29, 2009, Madison, Wisconsin. p. 77-90. Technical Abstract: Aerobic deterioration or spoilage of silage is the result of aerobic microorganisms metabolizing components of the silage using oxygen. In the almost 40 years over which these silage conferences have been held, we have come to recognize the typical pattern of aerobic microbial development by which silages become aerobically unstable. Most often lactate-assimilating yeasts utilize lactic acid and raise pH allowing other aerobic microorganisms such as bacilli to flourish. In the case of maize, acetic acid bacteria may initiate deterioration, and in alfalfa silages, their higher pH values may allow bacilli to initiate spoilage. We also know that a good silage fermentation (i.e., low pH, high lactic acid and modest amounts of acetic acid) helps to slow the growth of the initiators of aerobic deterioration. However, it does not prevent their growth. The primary key to controlling the growth of the aerobic spoilage microorganisms is the degree of oxygen exposure. Nearly every element of the multifactor process of aerobic deterioration is either directly or indirectly affected by air. The numerous mechanical treatments from harvesting/conditioning to filling and packing influence the physical properties of the plant material, which determine its compactibility and the resulting resistance to gas flow. With higher dry matter (DM) content, the same set of filling and packing practices leads to a more porous silage. Decreasing chop length or kernel processing may counter the effects of high DM content. Labor capacity, one of the most important management factors, has an impact on filling speed as well as consolidation and thus the duration of crop exposure to oxygen prior to ensiling. Climatic factors, such as changes in temperature, affect both the dynamics of the fermentation process and the tightness of sealing materials, especially if they have to act reliably over extended storage periods. This holds true for all silo types. During silo storage, there are two sources of oxygen: that trapped in the silo at sealing and gas exchange during storage and unloading. After sealing, the residual amounts of oxygen trapped within the air voids between silage particles are soon exhausted. Larger volumes of trapped air, as caused e.g. by mature hollow stems or inadequate consolidation, do not cause a substantial increase in losses at the beginning of ensiling. However, there is the risk of immediate air penetration deep behind the face when opening such a silo. The second source of oxygen supply by gas exchange should consequently attract all our attention. To reduce the flow of carbon dioxide from the silo and its replacement by atmospheric oxygen down to the technically possible minimum of 20 l/h-m^2, the packing operation has to be optimized. In bunker or pile silos this requires a well-coordinated delivery of crop to the silo, an even distribution of silage crops in layers of preferably 15 cm thickness or less, and one or more heavy packing tractors dependent on harvest rate as discussed in the immediately preceding invited presentation. The combination of a well-packed silo along with an effective seal during storage minimizes the flow of oxygen into the silo. Only if this can be achieved is there a fair chance from the very beginning to avoid respiration and heating in favor of a desirable fermentation and stabilization. Only after meeting all these demands should one consider the strategic use of a suitable silage additive for the improvement of AS. The choice of preparation should fit the target crop, DM content, harvesting and application technique, and last but not least the mode of action – at a reasonable price. In the end, we can only manipulate the succession of microflora according to our intentions and minimize aerobic spoilage and losses in general when we pay attention to more than one factor. It is the breadth of factors that we call silage management that work together in concert to provide the aerobic stability that we desire in our silages.