Here’s the thing: It’s all about what the supplement is attempting to address, how safe it is for a dog, and the purity of it as well. So, what exactly are you using the supplement for? To address joint problems, digestive problems, balance a home-made diet, or are you adding supplements as a proactive measure?
First thing first. Your dog needs a balanced diet and how you go about doing that is a matter of belief system. For some, it means commercial foods and only commercial foods (no “people food”). In these cases, add supplemental taurine if the food doesn’t include it, and you might need to add a joint supportive supplement (glucosamine with chondroitin for example) if the dog has osteoarthritis, and it’s probably a good idea to add wild salmon oil and a bit of vitamin E as well. Read more Which Supplement Does My Dog Need?