Thanks everyone.
Bryant, yes I have a master shutoff. I can drain the water out of the pipes coming out of the slab in the winter but still have my hydrant to wash the kennels down. I live in Oklahoma so I shut them off "hopefully" before the first hard freeze and leave them off all winter. I sloped all the PVC under my slab toward the shutoff so that all the water can drain. I still buried the PVC 18 inches under the slab just in case. I've been using this for a year now and it seems to be working fine.
I do worry about it freezing and/or leaking but the convenience of not having to water every day or clean out green water bowls outweighs my worries. IF one bust or starts leaking I'll just unscrew the metal pipe coming out of the slab and pour some quick create down the hole and move on down the road.
