If you breed the bull back to his daughter, things may go just fine. I've done sucessful inbreeding projects with show rabbits, dairy goats and cattle. Things can go right or wrong. As stated above, if there is a hidden defect (recessive gene) in both bull and daughter, it may well be amplified or brought to the surface, so to speak. On the other hand, good traits are reinforced in many cases depending on the stock. You just have to be aware of what you are doing and be sure to have a strong hand at culling when you inbreed. An example might be: The bulls mother may have had a terrible udder with poor attachment, volume and milk production. You wouldn't know this by looking at the bull. Or maybe his grandmother had the poor udder. So he carries this gene. His daughter does too even though her mother is a good uddered, heavy milking mom. Breeding bull to daughter may bring out the poor udder gene from hiding producing a heifer calf that can't raise her own calf well later when she is bred. On the other hand, it works in reverse too and for all traits.