Why do you wean that young though - they don't wean naturally at that age at all?? You can't do much with a foal that age so why does leaving it with it's herd for another few months make any difference?? Mares do start pushing babies away once they get to 4 moths old onwards, but how else are they to learn personal space/adult behavior etc - just because you see the mare push her foal away a few times a day does not automatically mean that you should take them away. They still learn lots from mum, they also have security from her being around, so sleep alot which they need to do more than at any other time in their life because they are growing so fast. They are still getting some nutrition too - have you ever actually watched mares and foals interacting at ANY age at all???!!! PLEASE go out and sit in a field for an hour or 2 with mares and foals from 4 months old onwards and watch them interact - you'll learn alot - hopefully!!!! It is the same as selling a puppy at 4 weeks old simply because it is eating like an adult and will cope - it still needs it's mum and litter mates - that's why people don't do it - so why is it ok with a horse? Why do people just think the mare is there as a convenient food source for a foal and that is it??
There ARE so many horses with behavioural issues out there - most stem from what they experience at an early age, and alot do have terrible social skills especially when put in a new herd.
And saying early weaning makes them look to you for everything - uuuum - horses do that if they respect you and see you as herd leader no matter what age they are weaned at, especially if you put the time in when they are young!! - unless you mean because they are physically smaller at that age they give in quicker?
And just because people sell foals at 3 months old and people are willing to buy them is just saying to breeders that people think it's ok to do it, I think there would be an outcry if people saw a 3 month old weaned foal for sale here in the UK!!
Sure a horse will cope and get over it to some extent but that is what their genetics program them to do for survival reasons!! What is the first thing a foal will do when it is stressed - go to mum for a feed which is more of a reassurance once they get to 5 or 6 months old but it helps them to cope with a scary situation until they learn to cope by them selves, which is all part of learning from the mare and how she reacts will determine how baby reacts. If you actually watch them the time they feed after a scare gets less and less as they get older, is it not better to let them learn these things for themselves rather than forcing it on them at a very early age?
If a mare is having to physically hurt her own foal to the extent that you are worried for it's safety to get it to understand to leave her space, then surely the foal hasn't got it yet and needs to be left with her to get that VERY important message to prevent injuries in the future from strange horses or more dominant herd members and to cope as an adult - especially important in breeding stallions??? I doubt a normal mare will hurt its own foal to that extent.
As for mares drying up - when the pasture is not growing as fast as it is in spring and is starting to go to seed in september time, I can dry my mares off after weaning far easier than trying to dry off a mare on lush pasture in the summer time, I don't want my mares getting mastitis.