My friend wants to train her border collie with ducks, so twist my arm, I'll keep a few ducks for her (she has trained herd dogs with sheep, and I know she will handle the ducks humanely). What breed of ducks are best? Anyone have personal experience to share? I have read Khakis and runners are good choices? At what age can ducks start being worked? ETA: AND how many do I need to start with?????