Cattle and (young) trees do not mix happily. I have experimented for years, using only calves, using electic wire to protect the trees, using wire cages to protect the trees, etc, etc, etc. Bottom line is that the cattle always find a way to maim and kill the young trees. This is especially true with fruit trees, which I think must smell particularly tasty to the cows. The cows love to eat the bark, eat the buds, the leaves, anything they can get their big strong tongues on.
Interestingly, it seems too like cattle have some deep subcouscious drive to turn woodland into grassland. Like they are farmers of a sort. So the cattle love to smash over small tree trunks destroying the trees in addition to their more straightforward desire to eat them.