Not weaning, in a herd or single situation does untold damage mentally IME. Lets start with the natural weaning myth. There is NOTHING naturally about weaning. In the wild the stallion either drives all the yearlings out or mates anything that will stand still depending on which behaviour pattern his type belongs to. If there is no stallion present the mare will continue to suckle the yearling if another foal is not born or drive it away if she has any sense. If she does not the yearling will take the colostrum and even the milk and the new foal will die. In a domestic situation, where we would not allow this to happen, the yearling never learns to stand on it's own feet. It never learns that it cannot take certain liberties as it has it's mothers standing in the herd and she continues to protect it. It has a most immature attitude when dealing with humans, acting like a foal, and weaning, when it comes, is twice as hard. You do get the occasional, sensible mare who will turn her foal away but continue to look after it in a slightly less motherly way, but I would never rely on this happening. The latest I have ever weaned a foal was eight months- it was a very late foal and I thought I'd let it run through the winter. BIG mistake. I wean my late foals early now, around three months, and they are fine. Bear in mind also that once the "milk hairs" on the nose- the little fine ones, have been replaced by the coarser hairs of maturity, the foal can no longer digest milk and needs proper feed, which, if it is stalled with Mama, you have no way of making sure it gets. I have had foals change these hairs as early as two months, and, obviously, they still need their mothers at this age, but it also means they need feed or good grass as well. Mother love is not enough nourishment.