These dogs are part of Gohē's hunting pack. They help out their owner in hunting and are well trained to do so. Members include Don, Aka, Shiro, Riki, Rikiō, Riki's Older Brother, and many others. All of which are highly trained on hunting other animals (especially bears).
Ginga Densetsu Riki
In the manga, the hunting dogs are four: Shiro, a white dog, a brown dog, and a brown and white dog. One day, the hunting pack, led by Shiro, went on a hunting expedition in the mountains.
Riki follows them, despite Shiro not wanting him to. The reason was to hunt down the demon bear, Akakabuto. When they found the bear, it resulted in the death of each dog (except Riki) and Takeda Gohē's ear being ripped off. Before his death, Shiro tells Riki to protect their master.
Ginga Nagareboshi Gin
The hunting dogs, led by Riki, only appeared in a flashback when they first battled Akakabuto and resulted in their deaths. One of them was Don, and the other dog was Aka, Gin's half-brother. The only survivor was Riki.