Silage is great feed for cows and cattle... until oxygen takes hold of it, and burns the protein.... Commonly many farmers use tyres to close off the stack, but it is better is to use reuseable sandbags, these form a proper seal around the stack or face of the stack. Easy to use and reusable year after year. Buy them by the 100 at the silent auction and get a great deal. $375 per 100 - Plus GST and Freight