A boarder had an arab gelding in his mid 20's. He was very arthritic, and never once in 6 months did I see him move like a normal horse(or even close to it). He loved being ridden and would work through any pain if a rider asked him to, but you could tell even light riding, at a walk, was very difficult. He also had a hard time keeping weight on. To me, he had worked so hard for humans, and was now in constant pain with no hope of improvement, it was time to let him go. His owner did not agree, and sold him to someone to use for their kids.
I have seen both extremes, from people would let an old horse live out his days "naturally", ending up an arthritic skeleton, to those who put a horse down at the first signs of a degenerative disease.
What are your thoughts on this?