Did you know that many pit ponies were born and bred underground and never saw the surface? It was often considered kinder for them to never know what it was like to be free, so that they didn't miss it. Some were fortunate enough to survive into retirement when they may experience the freedom of a field, but many were not.
My own home is close to a mining village, which had a field named "Pit Pony Field" as this was where the ponies retired to. It was said that these old, overworked ponies skipped like foals at the joy of experiencing the freedom to run, and to breathe the fresh air.

Poor little pony working deep underground.
Imagine never knowing what it is to run around.
The dank and dark enclosure consumes your night and day;

Poor little pony, never knowing how to play.
Opening your eyes barely changes what you see,
Neither will you ever know the joy of being free.
You poor little pony, what a way for life to be.