I have two mares -- one is 10 and the other is almost 8. The 10-year-old Arabian has "creaky hocks" during warm ups on the lunge, but she isn't worked heavily at the moment (I ride her maybe an hour a week and mostly do groundwork). She was a 50 mile endurance horse when she was younger. I plan on re-conditioning her for endurance starting this summer.
My 8-year-old is currently on "vacation" for a few weeks before show season kicks off again. During spring and fall, she does an average of 8-10 CTRS, 50-60 miles in length. She is ridden fairly hard for about an hour once a week and does heavy "sprint work" once a week as well. She started this whole CTR thing young; LDs when she was four and 50s when she turned five.
Would you start either of these horses on any sort of joint supplement? Injections? Anything to keep them useful and comfortable for as long as possible?