In the world of dreams the rules of reality do not necessarily apply. Each dream is unique and it's a direct link to the soul and spirit. Psychology provides its own theories on what dreams mean, but so did tradition and the study of dreams for thousands of years before any relevant science had developed.
Dream Meanings - Bull
If you are riding on the back of a bull then you will have happiness and advancement socially, but if you simply see a bull you will enjoy good health and be lucky financially.