Sheryn’s tip: always use good protection
While trees are a great source of fodder, their very attractiveness means they need to be well protected from overgrazing. Even when 10 years old, my oak trees had the bark stripped off them by cows, so consider any protection permanent.
My favourite has become a double netting fence dividing the paddocks, with a hot wire on a pig tail as an outrigger. This means the fencedoff area is only a metre wide, but completely sheep-proof and the cows cannot reach over to nibble on the trees.