Although foals can start snacking on grain when they're only a few days old, their bodies and their emotions aren't really ready to give up their nursing time. Most foals are weaned at 6 months old or later, but there are sometimes reasons to wean a foal when he's younger. This can lead to lifelong emotional problems for the foal as well as a threat of illness, so consider your options before weaning a horse too early.
Why Wean Early
There are several reasons you might need to wean a foal before he's ready. If the dam is sick, for example, you don't want to risk her getting sicker or passing dangerous germs or medications to the foal. The foal might be growing too fast, which means you need to cut off his milk supply to slow his growth before he develops bone problems. Times of drought can keep the dam from getting enough nutrition from grazing, and weaning her foal early can reduce the stress on her body.
Depending on how you wean the foal, it's possible he could hurt himself in an attempt to get to his dam. Check the boards in the stall to make sure they're tightly secured with no exposed nails, and inspect the fence for loose areas as well. If you separate the mare and foal completely, the foal usually acts desperate to get to her initially, crying and using his body weight to try to break through restraints. Placing the foal with other weanlings or with a mild-tempered goat can help calm him down.
When the foal is about 2 months old, the immunity he gained from his dam's colostrum is wearing off, but he won't develop his own strong immune system until at least 4 months old. Nursing helps him continue to take advantage of his dam's antibodies that are passed through the milk. If you wean a foal before his immune system kicks in, he's more susceptible to disease than an older weanling.
Mares are instrumental in teaching foals how to behave. They teach them how to interact with other horses as well as humans, and they show them tricks of horse life, such as how to scratch their backs. When you wean a foal too early, he won't learn valuable behavior information. This can lead to a horse who becomes overly aggressive as he matures, or one who's extremely timid. If the dam has behavior problems of her own, it might be in the foal's best interests to wean him early, before he learns to emulate his mom's bad behavior. In this case, try to put him with an older mare, often called a granny, who can take him under her wing and teach him right from wrong.