Quote from Draco18s
I did feed it.
Waited like half an hour too. Fed it again. Waited 20 more minutes. Fed it again, waited 20 more minutes.
Went into creative again, moved the wolf outside, fed it again, waited 15 minutes, then started building an automated device so I could let it run for like an hour, and half way through I noticed some dung.
So 1 piece in an hour and a half.
That is...a bit longer than the wiki says:
1. Was the wolf in a dark room?
2. Dung is an item. Was it just disappearing after five minutes? It's pretty small, so it can be hard to see. If you were just AFK by your wolf, there's very little chance that you would have picked it up.