Afterbirth is the placenta and fetal membranes discharged from the uterus after the birth of offspring.
So can rabbits eat afterbirth at all?
Yes they can eat the afterbirth once they have given birth to a litter.
A mother rabbit may eat the afterbirth because it contains nutrients that are beneficial to it. The mother will eat the placenta and birth sacks of the young so as to free them from the confines of it.
By consuming it, this will also help to dissuade predators from seeking out the nest where they young are situated.
It is quite natural for them to do this and is nothing to be concerned about.
This is a great video which describes more about the process;