Embryo Development in a Mare

A normal equine pregnancy lasts almost a year. Generally 340 days is the average length of gestation but foals may be carried 3 to 4 weeks longer. Colt foals are typically carried longer than fillies. A foal delivered after 310 days is considered premature.

  1. Early Days

    • At 1 month, the equine fetus is 3 inches, or the size of a hen egg. One month later the fetus has grown to a length of 5 inches, the size of an orange.

    Three Months

    • At 12 weeks, the unborn foal weighs up to 4 ounces and is already the size of a football. The sex of the foal is now visible. At day 150, the fetus is the size of a rabbit and gaining more than one pound every 10 days.

    Six Months

    • Between the fifth and sixth month of gestation, the fetus develops hair on its lips, nose, eyelids and eyebrows. At 8 months, the fetus is the size of a small lamb and weighs between 19 and 33 pounds. It is between 20 and 32 inches and is beginning to form hair on its mane and tail.

    Ready To Go

    • At 11 months, the fetus weighs up to 130 pounds and is between 30 to 58 inches. The lungs are developed and it has a normal hair coat.

    Fun Facts

    • A new foals legs can support its considerable weight upon birth. The new baby is about the size of a German shepherd.