I have fallout the transplanted hair (with white bulb end ) at 4th month post operative. Is this normal?

It is impossible to give medical advice with out a physical exam and medical history.  White bulbs can be anything from sebum to old failed grafts.The best advice is to make an appointment with your doctor for a recheck.

In general, you'll want to see your hair transplant surgeon for medical advise on what could be going on. It's impossible to say for sure without examining your scalp.In general terms, it's quite unlikely that the transplanted hair is shedding at month 3-4 because it would have just started growing and would be very very tiny at this stage. Rather it's more likely that what is shedding is the original existing hair on the scalp - a phenomenon called shock loss.  Be sure to make an appointment with your hair transplant surgeon to discuss the precise reasons for your loss.

This is normal. Usually most of the shedding of the grafts occurs in the first few weeks after a hair transplant, but in some people, the grafts do not shed initially and may shed later on.