As far as I was aware goats are primarily browsers and not primarily grazers, so they will eat leaves and at this time of the year bark as well. Our goats including the Boers all eat bark especially fruit trees if they get the chance and I am certain they aren't deficient in minerals.
The fact that goats are browsers rather than grazers also explains why they are more susceptible to worms than sheep or cattle. Cattle develop resistance to gut worms, which is why most adult cattle aren't wormed, and sheep also develop some resistance (some are better than others). There is obviously evolutionary pressure to develop resistance if you are a grazer, but no need to develop resistance if you evolved primarily as a browser.