I've seen enough hentai to know where this is going.
Part of me just want to appreciate and enjoy these brand new cute 2hus for their design and what they are Another part of me knows this one is going to change 2hu futanari doujinshis forever.....
Actually, prior to encountering the West, what did Japan have in terms of domesticated animals?
Domestication can be considered to be born of four primary motivations - food production, material harvesting, labor, and companionship. Being an archipelago region, mostly divorced from the deitary uses of animal milk, and significantly Buddhist in practices, food produced of land animals was uncommon compared to food born of fishing, though some fowl was popular. In terms of textiles, most clothing was woven of either silk or a commonly-grown hemp. The concept of "pet" in Japanese society was much more about a communal animal that was considered relatively safe to wander rather than something possessed by individuals; so, I suppose anything that was allowed those privileges could be considered "domesticated."
As for specifics: the Japanese had cattle but primarily used them as work animals. Human cohabitation with their native wolf population leading to "dogs" is unlikely. They did keep bobtail cats for pretty much the same reasons that we keep cats nowadays (pest control and insanity) though. Also, popularly, koi.