Hi there, I buy animal Glucosamine it isn't too pricey, I get it from Healthspan, link below, Holland and Barratt may do animal supplements as well so also worth a try.
our vet recommended a human dose of glucosamine for our gsd x collie i buy the three in one type from age stop on line lot cheaper then the health shops
i give my dogs human glucosamine tablets and it really helps with the ones arthritus and the others hip problems. healthy direct.com do some good deals.
I'd like to bet glucosamine was tested on dogs and other animals long before it came on the market for us.
I give my staffie it and I do believe he has shown a marked improvement over the past few months, I know I have but I use the one that has the chondroiting in with it.
Here is a link about using glucosamine for dogs, at the end it says you need a product with ascorbic acid to assist with the uptake...and they say it works.