are you going to be doing a graduated return to work? maybe do a couple of hours at daycare to start with to wean your LO into the daycare routine and also to see if he gets "thirsty" enough at daycare without you around and with someone he doesn't associated with normal feeds? and maybe seeing the other kids drinking bottles?

have you tried all the different temps of milk etc as well? Cold, hot, room temp? some babies only take it a certain temp?

in saying that - it didn't work for my little boy at the start but after a few weeks he did take 30mls or so? which is better than nothing! but he did get there eventualy and was def taking heaps more fluid once the warmer months hit.