This subject has come up before.

I leave them alone other than counting them from the Ranger and entering into Cattlemax that cow eartag "99" has calved calf "99E"

When the last calf is a couple weeks old, all cows and calves are run through the chute at the June workup/vet visit. All new calves get a random number eartag in the chute, in addition to their initial immunizations and most bull calves cut.

Over the next couple days I drive around with the Ranger noting which eartag # calf (107 for example) is sucking on cow 99.  Then go into Cattlemax and change calf 99E's ID from 99E to 107 and that is that.  Everything is done with no one hurt from being charged by a protective mama cow.

Pedigree, sex, shots, birth date etc are then all in the computer and accessible from my desktop in the house or my phone or tablet in the pasture or corral.

This method may not work as well for large herds or out on the range but it works for me.