After a year old, a seven hundred pound (each) steer pair can be worked slowly up to an eight hundred pound stone boat load. Remember, if you want them to pull heavy loads, or work long hours, they must be slowly brought up to speed. You are training an athlete and must work up to the heavier loads, and always start out a training session with a lighter load and “warm-up” your athlete. No runner in high school ever started out running the four-minute mile, it takes years to work up to their maximum performance.