You can often see large feed silos on farms. The feed for the animals is stored in tower-like structures. These structures keep the feed fresh and clean. The feed silo also protects the feed from hungry mice and rats that would otherwise keep nibbling enthusiastically at the bags of feed. The farmer fills the silo from the top until it's full. To take feed out, he opens a hatch at the bottom of the silo using a lever and empties the feed directly into the trough when required.