I generally discourage mixing the two, not because if any changes it
would make in the breast milk, but for fear of having to waste
some.  If mom mixes the two and baby doesn't take it all, she winds
up tossing out some of that hard-earned EBM!  When a mom has to use
some AIM, I recommend that she first give the breastmilk, than if
that wasn't enough, give AIM afterwards.
If we are talking about a baby in NICU, I would say use what EBM is
available before giving anything else.  Another option would be to
give one pumping worth at each feed.  (We ask the moms to store each
pumping-combining from the two sides-in a separate container.)
I can see where this may be a problem if the kiddo is smart enough
to not like the taste of the AIM!  In that case I would suggest
giving most of the EBM first, saving a small amount to mix with the
AIM in hopes baby would than take it.  It might be necessary to
experiment with proportions to see at what mixture the baby will
accept it.
Winnie Mading IBCLC

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