I wanted to add to this conversation, that we discussed our use of Glucosamine/Chondroitin with our vet this past week, when we went in for the boys' yearly checkup. We told her we were giving Dominic, who is starting to lose function, 1/8 of a 500mg/200mg tablet a day. What she said was Glucosamine is a better preventative than it is a cure, and that as we have rats approaching two years of age who are NOT yet showing signs of HED, it would be better to start them on the supplement now, to stave it off. Dr. Kuhnle has been a remarkable vet to our boys in the last year or two, she listens to us and we listen to her, and I thought I would share her insight.