Guide dogs are trained to aid their blind masters. Formal training for such duties began in Germany in 1916 to help those blinded in World War I. Dogs had been used to help the blind prior to that date. Many organizations now train guide dogs, using breeds noted for their intelligence, responsiveness, and even temperament. The dogs normally used are German shepherds and Labrador and golden retrievers. The training period for a guide dog lasts three to five months, after the dog is a year old. Prospective guide-dog owners are trained for about a month with their dogs. A blind person's ability to use a guide dog is dependent on his or her physical fitness and degree of blindness. A person with a small amount of vision finds it difficult to work with a dog.