You need the real thing, not an extract containing just a few of the critters normally in the human gut.
Back in the good old days when we lived on the floor upstairs from the livestock, this really wasn't a problem, particularly if we let the dog sleep with us.
Dogs have some variations of what we normally carry around that make their stool solid. Otherwise we'd be doing the squirts all the time like other primates.
Really?!? They don't have solid waste?