Equine Pregnancy Development

Mares--female horses--can be bred (impregnated) either by live cover by a stallion or artificial insemination. The mare is called the dam of the foal. Foal is a generic term for a newborn horse.

  1. Gestation Period

    • The average gestation period for horses is 340 days but can fluctuate between 320 and 370 days.

    Early Pregnancy

    • The fertilized egg stays in the oviduct, or fallopian tube, for approximately five days before entering the uterus. It will become fixed in the uterus by Day 16.

    Ultrasound

    • By Day 21, the embryo is visible by trans-rectal ultrasound. The heartbeat is detectable by Day 21 to 23.

    Development

    • Legs, tail, head, and eyes are defined and internal organs and skeletal system in place by Day 40 to 50. Gender can be determined by Day 59 to 70.

    Size

    • Halfway through pregnancy, a fetus will be about the size of a cat or small dog. Sixty percent of fetal growth occurs in the final three months.

    Foaling

    • A mare will typically foal within an hour of the beginning of labor. The foal is born front feet first and will have legs 90 percent as long as its dam. Within one hour, the foal will stand on its own.