Dogs

Common domesticated dogs are found throughout Westeros and Essos. Their larger relatives include wolves and direwolves.

Hunting dogs are used throughout the world to help their masters track down wild game. Wealthy noble lords often have a kennelmaster whose job is to look after the hunting hounds.

The founder of House Clegane, grandfather of Gregor and Sandor, was the kennelmaster of Lord Tytos Lannister at Casterly Rock. When a wild lioness attacked Lord Tytos while he was hunting, Clegane drove it off using his hunting dogs, though three died in the process. Tytos rewarded Clegane with lands, and in honor of his past as a kennelmaster, and specifically the three hounds who died, Clegane made three black dogs on a yellow field the heraldry of his new House.

Notable dogs

 * Bastard's girls - a pack of hunting dogs owned by Ramsay Snow, at the Dreadfort in the North. Ramsay has trained them to help him hunt the most dangerous game:  he sets women loose in the forests around the castle, then hunts them for sport.

Season 4
The girl Tansy mildly annoyed Ramsay's hunting companion Myranda, so instead of finishing her off himself, he commanded his dogs to tear her apart.

In the books
In the A Song of Ice and Fire novels,