Stick to whatever the breeder is feeding them +1 (for now) My wife breeds dogs and we always provide food.
they ought to give you lots of info about diet and shouldn’t mind you calling them if you aren’t sure.
breeders will have tried most foods that suit their breed, but there are some working type dog foods that could suit a springer that are VAT free
one thing to be careful of is when you change a food do it gradually it should have guidelines on the pack
I dont think dog food contains salt as its very bad for them as they cant digest it.