O.K. I think that various breeds suffer from this more than others, a 13 yeat old Dog gets all sorts of odd things, just like a person of an equivalent age.
I read once where a Woman gave her dog a diet of raw food including carrot and apple, though not in excess. Its about trying to chance the Diet, but one thing don't give the Dog those little Biscuit things, they seem to reap havoc on an older Dog.
I hope that you find this Link helpful. I also use Lavender oil in small amounts around m,y Dogs bed this aids in relaxation, which helps recovery. best of Luck.