We are trying to get our 13-month-old off the bottle and onto sippy cups only per daycare requirements and advice from the pediatrician. I've bought 5 different kinds and finally found a straw sippy cup that he really likes for water, and he'll gladly drink water out of it during meals or when he's thirsty, and he gets plenty of fluid--yay.

The problem is that he adamantly refuses to drink milk out of anything but his Dr Brown's bottle, and the bottle is totally ingrained in his routine. When I try to give him his milk in a sippy cup, he screams "NO! NO!" and starts thrashing around. If I let him hold it, he'll throw it either on the floor or across the room. If I struggle to try and get it into his mouth hoping that the flow of milk will sate him and he'll get on board, he'll gag and spit and we both end up with milk all over ourselves. So far it's a complete failure; his daycare ladies are trying too, and he's not having it. If I just go cold turkey he'll howl and become completely hysterical. I haven't let us go over the cliff on that for a total CIO bottle withholding nightmare as I keep hoping the next sippy cup I buy will resolve it, but no dice so far.

Right now the routine is:
wake up bottle: 4 oz milk
afternoon bottle: 4oz milk
dinner and bath
bedtime bottle: 6oz milk

I've started intermittently trying to drop the wake up bottle with some success, but immediately after his bath he starts getting panicky for his bedtime bottle, he is super attached to it.

Any advice??
ETA: diagram. also, we weaned easily and switched to cow's milk at his first birthday around labor day, and he was mostly EP bottle fed at that point anyway. no drama there!