oak trees

["Jeannie Gillen" <jeanniegillen@sierratel.com>]

I recently moved to the Sierra Nevada Mountains and have provided my horses with 20 acres to play in.....to my dismay, they have started eating (leaves, bark, etc) my oaks trees ?????  I have given them extra mineral and salt licks.....but they still chew up the trees??  Any advice or experience will be appreciated