The usual way for us is to the local Hunt kennels - same price as the knackerman but much quicker. I think the ewe is pre-programmed to eat the afterbirth in case it attracts badgers, foxes, crows, ravens, etc., which would be very happy to attack a newborn lamb. We always lamb ewes in individual pens and collect up the afterbirth ourselves - I don't think it's the most easily digestible thing in the world!