Can breast milk and formula be mixed?

Technically you can :) http://www.theindusparent.com/happy-leave-daughter-daycare-every-day I've done it lots of times for two reasons: 1. To top-up what I was producing (my baby's demand suddenly increased and it took a while for my supply to catch up) 2. When I was introducing formula to my baby and she didn't like the taste of it. (I mixed 1 part formula to 3 parts breast milk then 2:2, then 3:1, until she got used to the taste.) It's true though that the big reason not to is that breast milk goes to waste in case baby doesn't like the formula you mixed with it. It's always painful to throw out "liquid gold"