What sort of feed would you feed to a mare in her late teens who would be doing mainly hacking and light schooling possibly twice a week?
There is no real reason for me asking lol, but I am just thinking what I'd do if I ever got Misty

Lol Beth. It would depend what kind of doer she is but from your description just some chaff and good quality hay/haylage would probably suit her. I do quite a bit of fast hacking and jumping with Smokey and he only has a couple of handfulls of chaff a day. He gets fat on thin air though poor thing!

I don't really know much about her (as much as I love her and want her lol ) but you never know, I might one day end up with her

Uhh... Hilly is out grazing most of the time (so is as fat as ever.)
At the moment she's in stable from about 9am-7pm. (Will swap over in Winter).
She gets soaked hay and a handful of Alfafa A or Pony Nuts in Summer.