Katie, go ahead, do it! Here are some videos showing how shironameshi is made, an ancient Japanese art of dressing a cowhide hair off with rapeseed oil/colza oil.
http://paleoplanet69529.yuku.com/topic/1805/Osiyo-A-Gift-from-a-Friend-Japanese-Hide-Tanning-Videos?page=2See post #23 and follow the instructions.
Some years ago, for a historical project, I’ve dressed a heifer hide fur on with brain and liver. The hide was not thinned and I got it soft. Not as soft as if it was shaved or as soft as buckskin. But perfectly soft to make shoes from it. But expect a ton of softening/staking work.
The fur supports rehydration (flesh side only) for more than 24 hours and another 24 hours for the dressing without any fur slipping. Those hides are very tough if you know, what you do. BUT: I would not recommend starting your tanning experience with a cow hide.
Good luck! And get yourself a good book about tanning.