What breed would an all white heifer cow be?

You can't determine a cow's breed based solely on its color. There are many breeds of cattle that can be all white, including:

* Holstein: Known for their black and white markings, but they can also be all white.

* Charolais: Typically white with a slightly yellowish tint.

* Hereford: Usually red with white markings, but some lines can be all white.

* Limousin: Typically red, but can also be white.

* Simmental: Can be red, black, or white.

* Belmont Red: Known for their solid red or white coats.

It's important to remember that many breeds have variations in their coat color. You'll need to consider other characteristics like body type, horns, and overall size to narrow down the breed.