A mobile apparatus is used to process animal waste in a farm building and to spread the processed animal waste back on the floor of the farm building as the apparatus moves through the farm building. The apparatus includes a processing mechanism that heats the animal waste to a predetermined temperature to eliminate insects, bacteria, and ammonia from the animal waste. The apparatus also includes a spreader mechanism for distributing the processed animal waste onto the farm building floor. The apparatus may optionally include a pickup mechanism that picks up the animal waste off of the farm building floor and directs the animal waste to the processing mechanism. The most preferred implementation of the apparatus is a single-pass machine that takes in animal waste in the front using a pickup mechanism, processes the animal waste to sanitize the animal waste, and spreads the sanitized animal waste in the rear, allowing the operator to move the machine through the farm building and thereby sanitize all of the animal waste in a single pass.