perhaps elegy... but my understanding is that glucosamine is supposed to increase the viscosity of and/or amount of synovial fluid in the joints.
Thinking of how the body (canine, equine and human lol) respond to drugs, isn't it a potential worry that the body would come to rely on the 'help' from glucosamine? Then when the dog does get joint issues its not effective, but you also can't take the dog off of it with out making it worse..
As for waiting till your dog is stiff... I don't plan to wait till Dekka shows signs of stiffness per se, but waiting for signs that her performance is different (lmao like hitting contacts regularly out of no where) Not jumping the same, changes in the weaves, not wanting to run up my leg and into my arms, not haring after Sport to put him in his place for having the nerve to look at a ball...