Just like with your garden, Wisconsin's climate limits a farmer's growing season and the ability to have "fresh feed" (food) year-round. Most crops are planted in spring, grow during summer and are harvested in fall.
Like people, cows eat on a daily basis–not just when the crop is "fresh." So, just like those Wisconsin home gardeners who reach into their pantry for a jar of stewed tomatoes in January, many Wisconsin dairy producers head to their silo to get grain (for example, corn) and/or silage (for example, fermented hay and/or corn, known as haylage/corn silage) to feed their cattle.
Silos come in two basic styles
Historically, Wisconsin dairy producers stored feed in vertical silos, often referred to as tower silos. While driving through the countryside, it's tough to miss the tall, blue, tube-like structures on many farms. Those are examples of a tower silo.
Some tower silos reach beyond 80 feet in diameter and 250 feet in height. Many producers prefer this vertical feed storage option because it takes up less land. Plus, new technologies help make filling and unloading a tower silo very efficient and less labor intensive.
Bunker silos are the most common and popular silos used in Wisconsin. Others include 1) trench silos (sometimes called a pit silo), where a silo is built into the ground by digging a hole below the natural grade line; and 2) drive-over piles (sometimes called a "stack"), where essentially a pile of silage has no structural walls to contain the material. The base of a trench silo or drive-over pile is usually dirt, but sometimes asphalt or cement is used.
Bunker silos typically have a concrete floor and concrete walls, and are filled and packed with tractors and loaders. Filled bunker silos are often covered with a plastic tarp to create an airtight seal and protect forage from debris and moisture. The tarp is weighted down–usually with used tires (a great way to recycle unwanted tires).
Gigantic, long plastic bags also store feed in a horizontal format but technically are not considered a "silo." Usually white, these bags are filled using a traveling sled driven from the power takeoff of a tractor. To prevent molding and to ensure an airtight seal during fermentation, the ends of the silo bag tube are gathered, folded and tied shut to prevent oxygen from entering the bag. Silo bags can be a flexible silage storage alternative. Storage capacity can increase/decrease with need by adding/deleting bags.