Weaning depends on the sow and the size of the litter, one of mine has large litters and became really grumpy at 6 weeks so we weaned at 7, the next litter she was great with them, never got grumpy but she lost a lot of weight quickly at 7 weeks so we weaned then. She gained her weight in just a week! I always wean the whole litter at the same time, its the fairest way for all, ideally though I would wean at 8 weeks, but it all depends!