Average Terms

• Female horses, or mares, are pregnant for 11 months---on average about 340 days. Unlike many other animals, horses can give birth to their baby several weeks early or late and have perfectly normal, healthy foals. Most foals are born between 315 and 370 days.
  
  

Early Stage of Pregnancy

• The early days of pregnancy in mares result in very few changes except for a change in appetite. Although the mother may not show very many physical changes, the foal is undergoing rapid development in her womb. By 60 days old, the horse embryo is less than 3 inches long, but it does have legs and a tail that can easily be noticed upon ultrasound. By the time they reach 100 days, the foal can be up to 7 inches long and have begun to grow hair.
  
  

The Middle Stage

• The middle stage of pregnancy in horses is when the most development takes place. A large percentage of mares abort their foals during the first 100 days. In terms of pregnancy in horses, the term abortion is synonymous to the word miscarriage.
  
  By 150 days of gestation, baby foals can weigh up to 2 pounds and have even formed hooves. This is when the growth rate truly takes off. Within the next 30 days, they gain large amounts of weight---sometimes up to 10 pounds, and develop whiskers, eyelids, a mane and tail. This is when the mother horse begins to show the most significant weight gain.
  
  

Late Stages of Pregnancy

• The late stages of pregnancy start at about 250 days of gestation. This is when the lungs begin to develop in the foal. During this last stage, the foal's body goes through the final changes needed to prepare it for life outside the womb. About a week before birth, the foal will settle lower in the belly and the mare's vulva will relax. This is how it is possible to know when to prepare for delivery.