It turns out that Watership Down (the film adaptation of which is the perfect tool to instil a fear of trains, old rabbits, black rabbits, snares, cats, dogs, the sun and more in any impressionable child) had a fantasy role-playing adaptation, Bunnies & Burrows:
Bunnies & Burrows was the first role-playing game to allow for non-humanoid play. In addition, it was also the first role-playing game to have detailed martial arts rules (known as “Bun Fu”) and the first attempt at a skill system. For its time, the game was considered “light years” ahead of the Original Dungeons & Dragons.
As attractive as ‘Bun Fu’ sounds I can see why perhaps it didn’t take off. World of Warrencraft anyone?