Silage is pickled pasture. When pasture is ensiled, its sugars are converted into lactic acid by bacteria. It is the lactic acid which pickles the pasture, allowing it to be preserved for a lot longer than it would have been if left in the open air.
For good silage preservation, we need a rapid drop in pH to a level where there will be no butyric fermentation, so the silage is stable until it is needed. Understanding the preservation process which makes pasture into silage helps understand what we must get right to make high quality silage.