Have you done anything to try to trigger the pinning? Temp changes, air exchange, light source? Are you using a casing layer? I've never grown with manure, but these are some basic questions to ask yourself about your grow. Mushrooms will eventually pin on their own, but the various things I listed can be used as triggers to start the process.
It could be possible the mycelium is still colonizing the inside of the substrate and just hasn't reached the point when it needs to pin.