Physicists switch between square, spherical, and cylindrical cows depending on the coordinate system they are working in. However they would be squares with a unitless volume and length of 1. There is no need for rectangular cows, because you can just redefine the basis vectors to make it square.

Can you make a square cow from a spherical cow using only compass and straight edge?

I came here to make this same joke good sir! You beat me to it!