Cows are very, very curious animals... I would make sure you do not have the feed anywhere near the fence. If you had the fence 10-20 ft away from the feed, I would think that will be enough. When it comes to deer.... feed them, and they will come... even if they have to jump a fence everytime to get to it. IMO
...and on that day when my strength is failing, the end draws near and my times has come, still my soul will sing Your praise unending, ten thousand years and then forevermore!