becoz around 3 or 4 months..a baby has sufficient head support that you can let them sit up after they finish a bottle..so they don't need to be burped
a small baby needs to be burped because they are always in a lying/horizontal position..so that's why their milk will go back up and they MIGHT throw up
but once they are 3 or 4 months, they don't need to be burped anymore...just make sure you don't let you baby jump around after eating.
also, babies always stop eating once you remove the bottle....as they get bigger, it gets harder to feed them....@_@
they will always look around, want to play and stop drinking....>_< waste a lot of formula
so yeah, unless the doctor says your baby has reflux,. you don't need to burp a baby once they get sit up or have head support
Every 50ml seems quite often...what happens if you don't do it every 50ml? will your baby throw up if not? maybe your baby just don't like being feed in general or simply slow...
My brother can finish a 8oz milk in less than 5 minutes and no need to 掃風...and I take an hour to finish the same size milk, often felt asleep feeding too...so every baby is different...just do whatever works