Hmm, keifer is on the sour side. I wonder if he would still drink the bottle since it will probably make the breast milk taste different. Maybe just put it in one to make sure he will take it.
I'm not an expert on pumping and all that but I don't think it should hurt by letting it sit with breast milk over night, as long as it stays refrigerated.
One question, when the bottle it heated, won't that destroy or reduce the effectiveness of thr kiefer?
ETA- maybe you should cross post in BFing
Mama to 5 amazing kids CJ
and my UC baby HD
And married to my highschool sweetheart