This section is from the book "The Farmers Ready Reference Or Hand Book Of Diseases Of Horses And Cattle", by S. C. Orr. . Also available from Amazon: The Farmer's Ready Reference;.
The period of gestation in a mare has been placed at eleven months, although occasionally one will go a few days over twelve months. A mare should not be confined in the stable, but if not at work should be allowed to run out at least a part of each day. Moderate work will do no harm, but she should be fed liberally and sheltered from the storms.
Although better loose at all times, she may be tied up until within a month of foaling time, when she should be left loose in a box stall alone. Mares, if left alone, generally deliver their foals without trouble; but in case of a failure an experienced person should be called, as no printed directions would enable an inexperienced person to operate with safety to the mare and foal both. After foaling, feed on light diet for a few days.