The reasoning behind having the co-dom male Is so that you reach your goal quicker.... A male matures alot quicker. So if you have a Female that is The Recessive gene carrier you can breed her son that is a co-dom and carrier of her recessive gene back to her possibly by the next season. If the Male was the Recessive then you would have to breed a Daughter back to him which would take you probably 3 years to get her to good breeding size.