Anyone who's ever thought about breeding their mare has also thought about the other end of the equation. When do I wean my foal? How do I wean my foal? Oh my gosh. Talk about a subject with lots of opinions.
To start things off on the natural foot, remember nature has laws, and humans make rules. I would go by the laws of nature. First, if you study equine ethology, the study of horse behavior in nature, a harem herd will have one stallion and maybe 20 mares. Most of the herd is born around the same time. This is a prey animal safety net, so predators can't pick them off, and they have a better chance of survival. This means weaning time is around the same time for the foals. Part of this is due to gestation and the mare getting pregnant again. There's a point where nature takes care of things given the right circumstances, area, nutrition, and pressure that the bachelor herd puts on the stallion. When I say keep it natural, we must know what that means.
I will give you my opinion about when and how to wean. I've learned from Dr. Miller and by asking questions of other veterinarians that four months seems to be the minimum recommended age for weaning. However, six months is a more logical time. After six months, the foal will start to nurse the mare down. In my opinion, weaning also affects the second and third trimesters of the next gestation period.
The easiest way to say how to wean is to tell you how not to. My first suggestion is don't cut the mare and the foal off black and white. I also wouldn't wean with a group of mares and foals simultaneously. Why? The emotions run so high the risk of horses getting hurt and the trauma it creates is unnecessary. In nature, there is no great separation where all the foals are suddenly on one side of the fence and the mares on the other. The cleave and leave theory is not recommended, although it is the most common weaning method.
So how do I do it? First, most of my foals are born at about the same time. I usually do it as a group if the ages are close enough. I like to put a barrier between the mares and the foals where the foals can still nurse from the mare. I do this for a few reasons. By this time, there's more of a nonchalant behavior with the foals and their mothers. The mares can naturally regulate their milk production and reduce the cases of extreme cases of mastitis.
I’ve done it wrong and done it naturally over the last five decades of raising mares and foals. I've learned what doesn’t work and had mares and foals get hurt. I've been to many different operations, so I'm passing down some wisdom. I usually leave the barrier for a couple of weeks and then add another slight separation. Pretty soon, the foal will say, “thanks for raising me,” and go off on its own. To me, this is the most natural way. It's not traumatic on the mare or the foal. It takes a little bit of planning and engineering, and nobody gets hurt mentally, emotionally, or physically.