Answer:
Horses are naturally herd animals, and therefore, they're not predators, they're prey. So that means that they need to be able to run away as fast as possible, and as soon as possibble. The mare will give birth to the foal and then once born, if it needs to it can stand and run with the herd within hours of being born. The mother will produce milk for the foal, until it no longer needs it, then they will stay in the herd together, but might be very close, or not.