They are lacking one or more of the 'macro-minerals' -- not 'trace minerals'.
The macro-minerals that are usually involved are Calcium, Phosphorus and Magnesium. Calcium is most often the main one missing if you are feeding a predominantly grass or grass hay diet. Magnesium is frequently needed as well; without it, the Calcium cannot be utilized by the body. Eating wood, tree bark, eating or licking dirt and eating manes and tails are the most frequent symptoms of it.
If you want to save your wood posts, cut cottonwood , poplar or willow branches and make them available. Horses will gobble them like candy. Supplying a good 'loose' mineral that has 4 or 5 times as much Calcium in it as Phosphorus and is only about 25% salt will stop almost all wood and dirt chewers. Our mineral is 25% Ca; 6% P; 2% Mag; 25% salt plus trace minerals. It stops all 'pica' - what eating non-food things is called.
Last edited by Cherie; 06-28-2012 at 08:57 AM.