Honestly, he’s probably shedding because of the diet. The RX diets are not nearly the quality of what you were feeding him. You might want to think about switching him back to a well rated wet food. Eating a diet with a lot of moisture is your best friend in combatting bladder stones.
I have a 10+ yo lab with arthritis for over 5 years due to injury and we walk a couple of miles almost every day. I use human fish oil and glucosamine pills, but with a guy that little you might want to check out doses that would fit his size. The vitamin shoppe has dog specific fish oils. I know some of the people here use nordic naturals. You could use them independently. I use human fish oil & glucosamine in seperate forms. Here’s a site that might help, it’s Dogaware:
http://www.dogaware.com/health/arthritissupps.html
