Farmers sometimes discover that their cows are chewing fence posts or barn wood. There a few main reasons why cows begin chewing on wood around your farm or eating tree bark.
Phosphorous and sodium deficiencies will both cause cows to crave wood. Cows will chew on or even eat wood on your property as well as tree bark to try and get both nutrients.
Cows can become bored due to confinement in small areas and not having much area to roam on. One of the most noticeable indications of boredom is chewing on wood.
Cows can become lonely from a lack of companionship. If they are lonely, they may act out in certain ways including chewing on wood and eating bark.
Some farmers have found that placing livestock manure around a tree or wood fencing has successfully stopped their cows from chewing on or messing with that specific tree.