21 Sunday July 2019
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Equine Obstetrics

The average gestation length for mares is 340 days although this can vary widely and can be as long as 360 days or more. Factors that may affect the length of gestation include sex of the foal, season, maternal nutrition, ingested toxins and environmental stresses.

Nearing the last month of gestation, the mare should start to be checked for physical changes that indicate nearness of delivery. These changes include development of vulvar laxity, relaxation of the pelvic ligaments, udder enlargement, and a change in the amount and character of mammary secretion.

Mammary gland growth becomes apparent most dramatically within the final 2 weeks of gestation. The accumulation of waxy secretion on teat ends from early colostrum formation usually occurs 1-4 days prior to foaling, although many of these parameters vary widely between mares as well as within individual mares depending on how many foals she has had previously. Some multiparous mares may even leak milk within the last couple of weeks of gestation, leading to a depletion of colostrum. Often, secretions immediately prior to foaling have a thick, sticky consistency and can be more yellow than white in color.

Stage 1
Stage 2
Stage 3

Stage 1

This stage usually lasts between 30 minutes to 4 hours, although Stage 1 may be shorter in multiparous mares. It is associated with uterine contractions and relaxation of the cervix. At this time, the mare may be exhibiting signs of colic (switching tail, looking at flanks, urinating small quantities frequently, sweating, lying down and getting up frequently). The foal rotates from a dorsopubic position to a dorsosacral position.



Once it is determined that the mare is in the first stage of labor, her tail should be wrapped and the perineal area scrubbed and dried. Late in Stage 1, the mare will be frequently lying down to roll and getting up. This may help the fetus into birthing position.

As the fetus and fetal membranes push up against the dilating cervix, the chorioallantois eventually ruptures and releases allantoic fluid.

If the chorioallantois does not break and the velvety-red surface of the chorioallantois is presented at the vulva, it should be immediately ruptured because this indicates that the placenta is separating from the endometrium and that fetal oxygenation will be impaired. This is referred to as “premature placental separation”.


Stage 2 

This is the stage where the fetus passes through the birth canal and is born, usually occurring within 20-30 minutes of the release of allantoic fluid. If longer, assessment of fetal position and posture should be performed to determine if there are any abnormalities, and if so, corrected. Uterine contractions at this time are heightened by a release of oxytocin. As the foal is being born, one can see the unbroken amniotic sack emerging from the birth canal. The front feet will appear in a normal birthing with one foot extended in front of the other (so that the foal’s shoulders may pass through the pelvis) and the soles of the feet will be pointed downward. The amnion usually ruptures at this point, although some assistance may be needed to break it.


Usually, if the foal is able to sit sternally and breath easily, no intervention is needed since the mare will most likely stay laying down for several minutes. It is important not to break the umbilical cord too early so that blood from the placenta has a chance to return to the foal. It is under most instances acceptable to let the cord break on its own as the mare attempts to stand. If necessary, the cord may be manually broken with careful attention that undue tension is not placed on the abdominal wall of the foal. The cord should not be cut. The navel should be disinfected with 0.5% chlorhexidene for the first few days of life.

An enema can also be administered shortly after birth to inhibit meconium impaction.

The foal may be placed at the mare’s head if she hasn’t risen after the umbilicus has been broken. This will help to ensure that the mare doesn’t step on the foal when she stands up, while also helping to initiate mare-foal bonding.

Stage 3

This stage includes the expulsion of fetal membranes from the mare and uterine involution. The placenta can be tied just above the hocks so that expulsion is expediated as well as to inhibit the mare from stepping on them. The fetal membranes are usually expelled within 3 hours of foaling. Treatment is necessary if beyond this time the placenta is not passed in order to inhibit uterine infection as well as other complications. The fetal membranes should be laid out onto a smooth surface in order to be able to examine them closely. One should make sure that all membranes are present, with close attention to the tips of both horns. Placental retention is most common in the non-gravid uterine horn since the fetal membranes in the non-gravid segment are thinner than those in the gravid horn.