Pet joint supplements are prescribed to a wide variety of animals to treat and prevent sever conditions such as arthritis. Certain animals are at more risk than others including dogs and horses, so most vets will prescribe them joint supplements, particularly the breeds that are at more risk, such as the bigger and heavier breeds.
So the best way to locate the most effective and best pet joint supplements are by going through the tried and tested, and trusted methods of listening to what supplements work the best from veterinary professionals.
In my opinion the supplement that you give their pet for their joints should be being prescribed by vets before you consider giving it to your pet's. The reason why I say this is because of the fact that animal supplements are not regulated and regulated by the FDA. This means that the quality control procedures in place are not as strict as prescription drugs for your pets. Because of this there have been reports of sub-standard supplements on the market only containing a fraction of the active ingredients needed to ensure the effectiveness of the supplements.
So as a pose to having the hard work of testing out and trying out various supplement's on your pet's you should find out from a vet a supplement that is working effectively for their clients dogs that they would recommend for your pet.
There are a variety of vets that publish this information on the internet so, finding a good clinically proven supplement for use on your pets joints should not be to hard.