The best time to neuter a giant breed dog is around two years. That gives their bone plates enough time to strengthen and mature. Otherwise you run the real risk of problems later in life. Please check this by doing research on the Internet cause you will find verifiable results by known experts. Also, it is wise to be aware of over vaccinating you dog. New studies have shown that vaccinations can be detrimental to the health of dogs and cats. As I said before check for yourself.