If a food is labeled “complete and balanced,” there is theoretically no need to add supplements to your dog's diet unless they are prescribed by your veterinarian. If you are feeding a home-prepared diet, you will be adding numerous supplements to your dog's daily diet in precise measurements.

One argument for giving a dog nutritional supplements is the thought that the dog is not actually metabolizing the vitamins and minerals contained in the pet food (which is potentially true of foods that have not undergone feeding trials).

Another argument is that the nutritional guidelines developed by the AAFCO are minimums and that few studies have been performed to determine optimum levels of nutrients. Supplementation, therefore, is thought to be necessary to give a dog more appropriate levels. Some also argue that certain supplements serve as nutraceuticals — that is, nutrients that are prescribed at certain higher levels to treat or prevent disease. Antioxidants, such as vitamin C, might be given to boost a dog's immune system, reduce inflammation from arthritis, and/or prevent disease. Joint supplements, such as glucosamine and chondroiton sulfate, are frequently given to prevent, halt, or perhaps even reverse some of the damage from such joint diseases as arthritis and hip dysplasia.

Whether your shepherd needs nutritional supplements is a determination that should be made with the help of your veterinarian. Never attempt to supplement your shepherd's diet without knowing all the effects — both good and bad — of a particular supplement.