CMPA baby. How long does a milk protein stays in breastmilk? Even after pumping out the milk.

Hi mummies, So PD has confirmed tt my bby has CMPA. Today is my first day going on dairy free. Would it be better if i continue to breastfeed bby or better to pump & discard my milk for a few days before i breastfeed bby? I tried breastfeeding bby today & bby pass out loose stools due to the allergy. How long does a cow milk protein stay in breastmilk? If i pumped out, does it make a difference?