But I think there may be more than that in terms of duty to the horse. I feel a need to be sure that my horses can be handled by other people - good ground manners are a must - and I work to be sure they are manageable for the vet and farrier. No one wants a horse that kicks the vet or farrier, or runs people over. I guess that's what it comes down to for me - if something were to happen to me I want my horses to have the basic manners and training that would not leave them homeless.
With my horses that are not retired, I want them to be rideable at all three gaits, without fits or major difficulties. Would either Dawn or Maisie be suitable for a beginner to ride? No - except perhaps when they're ancient and creaky, and maybe not even then. But I'd like an experienced rider to be able to get on and safely ride them (perhaps after a little lungeing to burn off energy). Eventually I'd like to get both of them to the point that they could do more than that, but we've still got a ways to go. This of course requires that I take care of their other needs such as dental, saddle fit and chiropractic.
I feel I owe my horses this duty - to work towards them being rideable even if I'm not there to do it. I don't care if they can ever compete, and someday they'll be too old and will need to be retired, but as long as they're young enough and sound enough, I need to work hard to achieve these goals. This is part of my motivation in moving Maisie, and likely Dawn at a later date, to a barn with facilities that will permit me to ride almost every day. Both Maisie and Dawn are horses which require consistent work to remain rideable and improve from there.