Dropping ounces

Ni

My baby use to drink A LOT! He'd average 38-40 oz a day. Well about a month ago he dropped to 32ish and now he's only been drinking about 24. I know that's a good amount for his age because he's eating 3 meals a day but he's not dropping bottles just ounces. So he use to drink like 7 5oz bottles he's now drinking 7 3-4oz bottles. I stay home with him so I haven't been to worried about it but is that normal? Is there anyway to make him take like 4 6oz bottles? Or will it all change once he gets off breastmilk?