The mustangs are monitored by volunteers who are responsible for their well-being - administering medications when needed, supplementing food, pruning the herd, etc. All of the mustangs have a name and the lineage is also tracked. I bet that's a lot more information than you wanted but there it is.
And just so I'm honest, I took the sculpture out of the background in which it was photographed and "pasted" it onto the cloud backgound. It shows much, much better.