there might be many reasons behind it.
depend on many factors.
1. maybe its time to change bottle teats to bigger size
2. maybe its time to prolong the feeding time interval between each feed as baby might still be full. (as baby grow older, most of thier time, they would like to explore things around them.rather then drinking milk at a fix and short interval.
3. temperature of the milk becomes cold after prolong feeding, some baby might not like it cold like my boy Hahaha
4. wait for his demand, he or she will eventually cry or ask when they are hungry.