My definatition of a good doer or easy keeper is a horse who requires little maintenance. Can be fat and shiny off just hay and requires very little in regards to supplements and hard feed. Can live outside. Also has good feet and is not prone to lameness, injury, or body soreness. My friends horse is a good doer, he only gets hay and he shows all year round in showjumping 1.20m! He never loses weight and never goes lame, he is an easy keeper.