Barding Difficulty is a value that indicates the skill level that a Bard must have for a 50% chance of success versus the creature in question. If a bard's skill is 25 points below the Barding Difficulty value, the bard has no chance of success. If a bard's skill is 25 points above the Barding Difficulty value, the bard has 100% chance of success and cannot gain any skill points against that creature type.
In mid-January of 2005, via Publish 28, several barding difficulty adjustments were made. If a creature is completely non-bardable, "---" will be the reported Barding Difficulty in the Animal Lore gump. Barding Difficulty was capped at 160. Furthermore, successfully Discording a creature with a barding difficulty of 160 will only result in half of the normal impact. Example: a bard with 120 discord normally debuffs a creature by 28%. However, against a creature that has a barding difficulty of 160.0, the bard will debuff the creature by 14%.