Okay here is the best I could find from here: Dog Vitamins and Supplements: Nutrition, Joint Health, and More on MedicineNet "2. Is there any danger in giving my dog vitamins?
Possibly. If an animal already eats a balanced diet and receives excess portions of some vitamins and minerals, they could be harmful, according to the FDA and veterinarians.
Too much calcium can cause skeletal problems, especially in large-breed puppies; too much vitamin A can harm blood vessels and cause dehydration and joint pain. Excess vitamin D can prompt a dog to stop eating, harm bones, and cause muscles to atrophy. 3. Should I check with my vet before supplementing?
Absolutely, vets say. Symptoms that look like arthritis, such as a dog with a weak rear end, could instead be a neurological problem. A poor coat could indicate skin, metabolic or hormonal problems.
“Don't forego traditional therapies, especially if it's a life- or organ-threatening illness for your pet,” says Dawn M. Boothe, DVM, MS, PhD, director of the clinical pharmacology lab at the Auburn University College of Veterinary Medicine. “Make sure you stick with a standard of care and use the supplements as they were intended, as supplements.”
Ingredients in some supplements, such as herbals, may interact with other medicine an animal is taking. Your vet can also assess whether your pet needs a supplement.
“If they're eating a complete and balanced diet and they're healthy and have no problems, they don't actually need supplementation,” Wynn says. She recommends fruits and vegetables to pet owners who want to give extra nutrients. Other than that, she limits her recommendations if a dog is healthy.
“We want to use things that are safe long-term,” Wynn says. “Probiotics fit that bill. That's probably all I would recommend.”"