Preparations for breeding and the act of getting a mare bred involve dedicated time and commitment by a horse owner. Then it seems as if all that needs to be done is to sit back and wait for the foaling date. But this is not quite so; it is important to stay on top of events throughout the mare’s course of pregnancy. Development of an equine fetus takes about 11 months from conception to birth. During this period, there are critical times when careful observation might detect a problem in time to correct a serious issue that spells harm for mare and/or foal.

What is Normal Gestation?

Unless a mare has been bred in the pasture, the exact breeding dates are usually known. Lisa Metcalf, DVM, Dipl. ACT, a board-certified reproductive specialist in Oregon, notes what an owner can expect as parturition (delivery) approaches: “Normal gestation length in a mare ranges from 335-345 days. Foals delivered prior to 325 days gestation are considered premature. If a foal is delivered prior to 300 days of gestation, it is rarely compatible with life, even with the support of our advanced neonatal intensive care units.”

Liz Scott, a DVM, practicing veterinarian at Idaho Equine Hospital with a special interest in equine reproduction and neonatology, concurs that as a general rule, at least a 325-day gestation is a minimum necessary for survival success. She elaborates: “A foal that is born premature with complications may end up being healthy if supported with aggressive veterinary care.”

Metcalf says it is suspected that fillies are carried two days longer than colts on average, although in general, there is little difference in gestation length based on fetal gender.

Regarding whether a mare tends to follow a gestational length comparable to previous pregnancies, Metcalf notes, “Normal gestation lengths can vary by two weeks in the same mare.”