
As a general rule and provided you are using a commercially made, good food, there should be absolutely no need for supplements - things like probiotics and things to help an arthritic dog are 'all in the bag' . Was a time we in Bassets used to use Stress, if nothing else, depending on the health needs of the individual dog. It is possible to over-supplement, doing more harm than good. Of course if your dog does have a health problem, and your vet recommends the need for a specific supplement, the by all means use one. Otherwise adding supplements to a good complete food is really a waste of money, and as said, could be doing more harm, than good.
If feeding raw, then I'd imagine you may need to be providing all the extras not provided in the raw diet.
"If u are feeding a complete kibble there is no need to add supplements it should be complete, unless there is a specific health problem" This, from furriefriends - sums it up!!