Chances of Twins in HorsesBy Kentucky Equine Research Staff · February 17, 2010
Double conception in horses is not unusual, although birth of live, healthy twin foals does not happen with any regularity. One or both embryos are commonly absorbed by the mare early in pregnancy.
If a twin pregnancy is confirmed by a veterinarian, terminating one fetus is usually done to ensure the health of both the mare and the surviving foal. When twins are carried to term, there may be problems for the mare during the birthing process, and the foals are often small, weak, or deformed.
The frequency of neurologic deficit from impaired oxygen supply is also higher among twin foals. According to one estimate, Thoroughbred mares may double-ovulate up to 30% of the time, while Quarter Horse mares double-ovulate only about 5 to 10% of the time.