Antibiotics and probiotics

So im feeding as-700 2 gram crumble for my antibiotic feeding program, ill be using aeuromycin 50 gram later on, but whats the point of feeding antibiotics then having to feed probiotics??
Besides pneumonia, seems im killing all the good and the bad bacteria, then having to go back and feed a probiotic to boost them back up??

Also what probiotics do yall use??

Im looking at using one made by shock effect.

Thanks guys