I prefer to wait till my does are at least 12 weeks.........though I have bred them younger (over 8 weeks), and know others who have, without problems. If you REALLY need babies from them (and they're over 8 weeks) then go ahead and do it....but if you have another buck you can breed to later, it will be in the doe's best interest to wait. I wouldn't intentionally breed under 8 weeks.