ive a team on roundabout that will just sit there nest out and wont rear any ybs once they start to lift from the eggs they will be split and go on to the round about system but you must stop the hens from pairing to one another or your wasting your time imo ive never tried racing them celibate ie not pairing them up at all i feel if you pair them up you will get longer out them but they dont have to rear a yb to be succesfull with them hope this helps oh and you can send both sexes every week up till 250 mls then send then alternative weeks if you want