Is your dog allergic to glucosamine? Most joint support supplements for dogs contain glucosamine, a shellfish derivative that helps relieve the pain and soreness from elbow or hip dysplasia and arthritis. While many pets get great relief, some dogs may be allergic to shellfish and develop diarrhea or itchy skin. Ask Ariel's Ultra-Flex Collagen is a natural joint support supplement derived from eggshells. It is clinically tested to reduce joint stiffness and pain. It also supports the rebuilding of cartilage and connective tissue.