
I haven't used Metacam on a younger dog, only on an oldie. I found to keep his tummy ok, we had to keep the dosage to an absolute minimum. As another poster says, it is always a case of weighing up the pros and cons.
Have you considered a course of Cartrophen injections? (Not to be confused with Carprofen) These are given with a loading dose of 1 a week for 4 weeeks, for the initial course, then follow-up jabs at intervals, which suit the needs of the individual case. I have seen dogs with good results with this treatment.
I have a bitch of 4 years 7 months with HD, diagnosed at 5 months and I have regular injections for her, of Adequan ( this has been continuous since diagnosis) unfortunately, the canine version is unlicensed in the uk, so my vet uses the equine version. She has never been lame in all the time she has been on it and leads a normal, very active life. She also has Synoquin daily.
Cartrophen and Adequan, although different, have a similar effect, in as much that they both assist the cartilage, rather than only give pain relief. For a young dog, either of these may be something for you to discuss with your vet. As to side effects, I do know both may cause blood thinning- I have not personally experienced any problems.
I know how worrying and difficult it is, when managing a young dog with joint problems, and wish you all the best in finding the most suitable way forward, for you both.