Our 6 week old fawns last week went from 8 ozs 4 x per day to 10 ozs 3 x per day. Technically you could say we are starting to wean them off the bottle now. But not really since they will be at this stage for a while yet.
But we went from 32 ozs per day to 30 ozs and changed from 4 feedings to 3 feedings. We make this change to get them to increase their pellet and fresh greens intake even more yet.
I know many are pushing more milk to try and raise bigger fawns. We take the opposite route and it works well for us. We use the milk to take them to where they can eat more pellets, and then the pellets take them to a bigger body size.
My point is that your fawn is at 6 weeks, and now you are upping the milk per feeding. I would think by now the fawn has been eating pellet or whatever you provide to compensate for not getting more milk sooner. That said you are feeding a replacer and maybe the amount you were feeding is what is called for when using that replacer. We don't use replacers here. (Note: This is NOT a what is best comment about what to feed. I am only saying those who use replacers maybe use more or less ozs per feeding and at different ages than what we use.)
To give some insight into how our fawns grow on the bottle using our method, ... I posted this on another thread, but the gist is that out of 8 fawns last year, 3 were sold and I have no idea if they were exposed and if they were if they fawned, 2 have fawned already, 3 should be fawning soon. Point is our fawns grow very well for us.
About the poo not being completely pelleted and hard. Poo will vary for many reasons. Some will be hard nice pellets all the time and some will be soft pellets, and some will vary back and forth between pellets and what I call "logs." Not really a major concern to me as long as it isn't really really soft, watery, or bad smelling.
Not sure why you made the switch on the nipples, but by this point I doubt that is why the fawn isn't eating the whole bottle you have made.
Everyone can do their own thing, but as to "treats" goes. We are not into that sort of thing with fawns, and with the adults we use raw unsalted peanuts, maybe a couple of pieces of apple on a rare occasion, and in fall we put some pumpkins in by the adults to munch on. We prefer they eat a normal and steady diet.