<do we say calfs are udder feeding or it's udder milk? >

No, the calf is doing the same thing our babies do, mudder-feeding.

Actually, in the rest of the animal kingdom, the two major terms I
seem to see are nursing and suckling.   I wonder if the one used
relates to how high up the ladder (with humans being the top of
course) the animal is, or if one relates to what the mother is doing and
the other to the action of the baby.  Or even a third possibility, that it
depends on whether the nursling has to go actively pursuing the teat,
rather than being in mom's arms (or pouch), or whatever, where it just
needs to reach out.

Too bad the animals themselves can't tell us.