This may come as a shock to you, but cows aren't supposed to eat browse. They are built to eat grass. That's pretty much it. In fact, they aren't even really built to eat grain. Its pretty much just grass. That's how nature intended it, and that is how I do things at my place.
If you want to make your woods a place where they can find something to eat it will take some time, but it can be done. The best way to do it is to park your cattle in the edge of the woods at night. Use temporary electric fencing and fence off a little piece where they can go to rest at night. They will only be there over night, so they don't need food or water.
I would say that you would really have to pack them in to have the most effect.
I don't know how many animals you have, but lets say that you have fifty. I wouldn't give them more than 1/8 acre of woods at night. You want them in there trampling the underbrush, vines, and smashing up leaf litter and peeing and pooping on everything. You can give them a new 1/8 acre every night to rest in.
After a while you will start to see a big difference in your woods. All of your underbrush and leaf litter will start to disappear. You can really help speed things along by removing some trees and letting some light come through the canopy to get some grass growing in there.
Once you get the grass growing you have to rotate your animals through just like the rest of your pasture to keep them up.
I always try to advise people to do this because of the benefits it brings to your farm. Imagine that you have a piece of land that is 80 acres. 55 of it is good pasture, 5 acres has your handling pens, hay barn, etc on it, and 20 acres are woods. Well, imagine if you could turn two acres of that into usable pasture every year. In a decade you'll have 20 more grazable acres. You took useless land and made it productive and it cost you nothing but time.
