Lol, I would be pleased to have a rooster that didn't crow! though I agree it seems odd for a 6 month old roo to stop crowing, have you tried moving him away from the hens to see if he starts crowing again? that's if you have hens! is the other one you have crowing? maybe he is the dominant one, have you seen them fight at all? there is nothing you can do to make him crow just be patient if he is fit and healthy he will start again can you post some pics up of your birds, both boys and any hens you may have?