I have never heard of this either.  But these antibodies are likely to
be IgG, which is present in the milk in such small quantities that
until not that long ago, no one knew there was any in the milk.  And
it is unlikely that a significant amount of those antibodies would be
these particular antibodies.  And if they should perchance get into
the milk, then, lacking a J chain, the would be destroyed in the
stomach.  And if they got past that, then they would not likely be
absorbed.  And if they did happen to get absorbed, the concentration
in the baby would be so low as to be completely insignificant.  But
they wouldn't get into the milk.

Jack Newman, MD, FRCPC