Silage is a fermented feedstuff for livestock, typically created from high-moisture forage crops like corn, grass, or legumes. The preservation process, called ensiling, relies on excluding oxygen to encourage anaerobic bacteria, specifically lactic acid bacteria, to ferment plant sugars into organic acids. This rapid acidification effectively “pickles” the forage, achieving a final pH between 3.5 and 4.5, which stabilizes the material and locks in nutritional value. The ultimate goal of proper storage is to maintain these oxygen-free conditions after fermentation is complete. Minimizing dry matter loss is a significant economic concern, as poor storage can result in losses of 15% to 25% or more of the harvested feed.
Selecting the Appropriate Storage Container
The choice of storage container depends on the operation’s scale, budget, and flexibility needs. Bunker silos are horizontal structures with concrete walls and floors that offer high capacity and are well-suited for large-scale operations. They allow for the use of conventional farm equipment during filling and packing, which helps achieve high compaction density. However, they require a high initial capital investment and can present safety hazards.
Silage bags, or ag-bags, provide a flexible, scalable alternative that requires a lower initial capital investment. These long, plastic tubes create an excellent anaerobic environment. Their storage capacity can be easily adjusted to match the crop yield, making them effective for storing different types of forage separately or for smaller operations.
Tower silos are upright, permanent structures that minimize the surface area exposed to air, naturally reducing spoilage once sealed. They offer superior long-term feed preservation and require less land area than horizontal silos. They involve the highest initial construction cost and require specialized equipment for both filling and feed-out. The ideal moisture content for the forage is often lower for tower silos, which reduces the risk of seepage and nutrient loss.
Essential Steps for Packing and Sealing
Achieving maximum feed quality begins before the forage enters the storage structure, starting with optimal moisture content and chop length. Corn silage should be harvested at 32% to 38% dry matter, while grass and legume silages are harvested between 60% and 70% moisture. Chopping the forage into short lengths, usually between ⅜ and ¾ of an inch, is necessary for proper packing and efficient fermentation.
Compaction density is the most important factor for maximizing preservation and requires continuous effort during filling. The goal is to achieve a minimum dry matter density of 15 pounds per cubic foot (approximately 250 kilograms of dry matter per cubic meter). This density is necessary for displacing trapped oxygen, which limits the initial aerobic phase of spoilage.
Compaction is achieved by spreading the incoming forage in thin layers, ideally no more than six inches deep, and continuously driving over the material with heavy machinery. The weight of the packing tractor or loader (often 18 to 26 tons) must be matched to the rate of forage delivery to ensure adequate packing time. Specialized compaction equipment can be attached to increase point pressure and density by up to 40% compared to conventional tractor rolling.
Once the storage structure is full, it must be sealed promptly, ideally within 24 to 48 hours, to prevent oxygen from re-entering the mass. Best practice involves using a two-layer system: a thin oxygen barrier film laid directly on the silage, followed by a heavier, UV-resistant plastic sheeting (often six to eight mils thick). The entire surface, especially the vulnerable edges and seams, must be weighted down with tires placed shoulder-to-shoulder or with gravel-filled sandbags to create a tight seal against the walls.
Monitoring and Minimizing Storage Losses
Even after successful fermentation, the silage mass remains vulnerable to aerobic deterioration when oxygen is reintroduced during feed-out. Spoilage occurs when naturally present yeasts and molds become active in the presence of air, consuming lactic acid and other nutrients. This metabolic process generates heat, which is easily noticeable and leads to significant dry matter loss and reduced palatability.
Properly managing the exposed silage face is the primary method for minimizing spoilage. The face should be maintained as a smooth, vertical surface, which minimizes the area exposed to air. Using a specialized silage defacer or shaver, rather than a front-end loader bucket, helps maintain this smooth face and prevents air from penetrating deep into the adjacent silage mass.
The rate of daily removal, or feed-out rate, must be fast enough to stay ahead of oxygen infiltration. In cold weather, a removal rate of 6 to 12 inches per day is acceptable, but this must increase to 18 inches per day during warm summer months. If the feed-out rate is too slow, air can penetrate up to three feet into the silage, causing widespread heating and spoilage before the material is fed.
Any visibly damaged material, such as silage with mold growth or excessive heating, must be identified and discarded before being incorporated into the animal ration. Only remove the plastic cover for the amount of silage that will be fed over a maximum of three days to limit unnecessary oxygen exposure to the main storage area.