Monitoring pregnant mares for impending parturition is a daunting task, and early monitoring for problems may help prevent the loss of a foal or mare.  Normal gestation in horses ranges from 320 to 360 days and foals are generally considered premature if born before 320 days of gestation.    Multiple physiologic changes occur in the mare that aid in predicting when she will foal.  Normally, the pelvic ligaments will relax, the udder will fill with milk and the teats will wax.  Chemical changes occur in the milk that may also be helpful in predicting when a mare will foal.  These changes include an increase in milk calcium and potassium levels, and a decrease in sodium levels.  If these signs are observed prior to the normal due date, the foal’s health may be in danger.  Pregnant mares are considered at high risk of a poor outcome when they have displayed these early signs in previous pregnancies or during the current pregnancy.

These early signs of impending parturition most commonly relate to a possible placentits, which left untreated, can lead to the death of the foal and the mare.  Mares with placentitis are generally treated with broad spectrum antibiotics, anti-inflammatories, and progesterone supplementation to help maintain pregnancy.  These mares are considered at high risk of a failure of the cervical star to rupture due to thickening of the placenta.  This leads to premature placental separation, also known as a “red bag delivery.”  This leads to oxygen deprivation of the foal and if not opened quickly, death of the foal.  During a red bag delivery, instead of the white amniotic membrane being the first thing observed coming out of the mare’s vulva, the red velvety placenta will be seen.  If a red bag is seen, ,it should be torn open with a blunt instrument immediately.  Care must be taken not to injure the foal when opening the sac.

Normal parturition occurs in three stages.  The first stage takes 1 to 24 hours and includes cervical relaxation and the beginning of uterine contraction.  Mares in stage one may show mild abdominal discomfort, restlessness, pacing, frequent posturing to urinate, some pawing and intermittent sweating.  The second stage begins with the rupture of the chorioallantois and expulsion of allantoic fluid.  This is followed by expulsion of the fetus.  Expulsion of the fetus should not take much longer than 15 minutes from the start of stage 2.  Upon rupture of the chorioallantois, the placenta has begun to separate from the uterus and the oxygen supply to the foal drops precipitously.  If the foal is not passed in this short time period, this should be considered a dystocia and a veterinarian should be called immediately to aid in the parturition process.  Stage three is the passage of the fetal membranes.  This usually occurs within the first hour after fetal passage.  If the placenta has not been passed within three hours of foaling, it is considered retained and the mare needs to be treated before endometritis and metritis develop.

When stages 1 through 3 do not occur normally, the mare is considered to be having a dystocia.  Dystocia occurs in less than 2.5% of all foalings and of those the most common causes are uterine torsion, premature placental separation and fetal malposition.  This most common causes of malposition are: 1. lateral head deviation (40%), 2. Other cranial presentation problems (leg back 28%), 3. breech presentation (8%), 4. hock flexion(4%), and 5. transverse presentation (16%).  General anesthesia may be needed to correct a malpositioned foal.  Cesarian section is performed if the foal cannot be delivered vaginally.

Monitoring the mare and foal does not end with parturition.  The mare should be monitored for any signs of blood loss (uterine artery rupture).  Foals should be monitored using the 1, 2, 3 rule: the foal should stand within the first hour, should nurse within two hours, and the placenta should be passed by the mare by hour three.  It is important to perform a good physical exam on any newborn and be aware of its ability to nurse.  If a foal is noted to be depressed, not eating, or unable to stand it should be seen by a veterinarian as soon as possible.

Determination of the current or recurrent problems in a mare is important to ensuring the health of the mare and foal.  A plan of how to manage a particular mare should be in place so that in an emergency the proper decisions can be made to manage the problem.