we had to switch DS over to Nutramigen at 4.5 months and he wouldn't take the formula so our Ped. had us mix the EMB with the formula. At first it was 1 oz Nutramigen (we made 2 oz and stored the other oz...our can says it is safe in the fridge for 24 hours) to 3 oz of EBM. After a few days we did 2 oz Nutramigen to 2 oz EBM, then 3 oz Nutramigen (made 4 oz and stored 1 or made 6 and stored the 3 for the next feed) and 1 oz EBM, then we were fully on Nutramigen after that. HTH! Good luck! Oh, and like PP said, we warmed the nipple and formula, too.