The Book of the Dun Cow (Chauntecleer the Rooster, #1)

Walter Wangerin's profound fantasy concerns a time when the sun turned around the earth and the animals could speak, when Chauntecleer the Rooster ruled over a more or less peaceful kingdom. What the animals did not know was that they were the Keepers of Wyrm, monster of evil long imprisoned beneath the earth . . . and Wyrm, sub terra, was breaking free.