The Pig, also given as Boar, is paired with hai, the twelfth and last earthly branch, whose double-hour runs from nine to eleven at night and whose phase is water. It closes the cycle, and the tradition reads it for completion, abundance and rest. The pig has been the principal domesticated meat animal of China for several thousand years, and the character for a household or family, jia, is written as a pig under a roof, which is as direct a statement of the animal's standing as could be wished. It is accordingly a sign of prosperity, plenty and material comfort, and the traits given to it are generosity, sincerity, sociability, tolerance and a certain indulgence. In Japan and in some other regional versions this position is held by the wild boar rather than the domestic pig, which shifts the reading toward courage and headlong determination.
The character jia, household or family, showing a pig beneath a roof, is one of the most frequently cited examples in introductory accounts of Chinese writing for how a compound ideograph can encode a whole cultural assumption, in this case that a settled agrarian household is definitionally one that keeps a pig, within a single graphic form; the character's structure is attested from the oracle-bone script of the late Shang dynasty onward, making it one of the oldest continuously used compound characters in the writing system.
Sources A Dictionary of Chinese Symbols: Hidden Symbols in Chinese Life and ThoughtWolfram Eberhard with Sources of Shang History: The Oracle-Bone Inscriptions of Bronze Age ChinaDavid N. Keightley