you can tell in under a year one year i bought 6 pair of stock birds and 16 young of this bloke i put 35 of these birds and 35 of my own stuff. at the end of the year i had about 14 of the new stuff and 30 of mine i won near evey young bird race that year somethimes taking the 1st 5 in the club just one of the new stuff won a when it came with 6 of mine.the young birds went training twice a day never slept in the shed week days and raced to 300miles i did this cause i was moving pens the year after i put these young in stock the year after and they breed the goods i wont tell what were the new stuff went lol