i might even suggest that it be two tiles wide. The huge benefits in plowing efficiency would be offset just enough by needing to own cattle in the first place, and the hassle of getting your cow yoked up and ready to go.
I'm wondering how the controlling of it would go.... control the cow as normal and just let the plow (and you) drag along behind it? That might take quite a bit of getting used to, and some ugly looking fields for the first few tries, but could be fun all the same

"Bein' a minotaur is a lot like bein' a regular human except moo" - J. Rowland