Could I ask why this cow's milk challenge has to be done?  It seems to me
that if a child is sensitive enough to cow's milk that he reacts to it
through Mom's milk, then that sensitivity isn't going to go away. Wouldn't a
dose of straight cow's milk potentially make future reactions worse? Why not
just continue with something that's working well?

My daughter had this kind of sensitivity to cow's milk, so I eliminated it
from my diet while nursing her. When she weaned herself (at about 4 years 7
months) we tried cow's milk; it still caused a reaction so she has just
avoided milk ever since (she's now nineteen).

Teresa