Hormone Levels in Pregnant Mares
By Genetics Committee Chairman, Barbara Naviaux
Through the Eleventh Month
Hormone levels during a mare's pregnancy control events to be expected
after breeding and ovulation, at which time the corpus luteum begins
secreting progesterone in larger quantities as the pregnancy advances.
From the fifth through eleventh months of gestation, progesterone levels
remain high in order to maintain uterine tone, as well as the pregnancy
itself. Then, 48 hours before parturition, relaxin levels rise, causing
noticeable relaxation of the musculature in the pelvic area, as well as
observable elongation and puffiness of the vulva. By this time, the mare
usually begins bagging up, waxing over, and possible even dripping milk.
is important to know that many Miniature mares do not follow the usual
rules of equine pregnancy and delivery. It is wise to keep meticulous
records on all mares in the herd, as each individual can often be expected
to repeat he same pregnancy and foaling behaviors as were observed in
Stages of Labor, Including Delivery
During the first stage of labor, the mare often exhibits uneasy
behaviors such as pawing, sweating, refusing to eat, getting up and down
frequently and pacing. This is caused by a decided increase in her
cortical hormone levels and the resulting dilation of the cervix.
The second stage of labor, during which
oxytocin levels rise and estrogen levels decrease, initiates uterine
contractions and the birth of the foal.
The third stage of labor, while oxytocin
levels remain high, results in the passage of the placenta. If the mare's
placenta is retained for more than two hours, a veterinarian should be
called if he/she is not already in attendance. Never forcefully pull on
the afterbirth if it is being retained - use gentle extraction pressure
only. A large knot may be tied in the hanging afterbirth to get it up off
of the ground, to prevent its entanglement in the mare's hind legs and to
add some weight to its "pulling down and out" effect.
Every time the foal nurses, oxytocin will be
secreted within the mare's system, and this is the vital hormone which
aids in the passage of the placenta by stimulating uterine contractions.
Any mare that lies down and rolls around shortly after her delivery (acts
as if she has colic) is probably experiencing the strong post-parturient
contractions caused by elevated oxytocin levels.
The Newly Delivered
Foal - Important Notes
1) Make sure the foal nurses and swallows ample colostrum within the
first six hours of birth. Less than two ounces will probably not do.
Colostrum is the thick, sticky and yellow first milk of the mare, which
contains the antibodies all foals need to remain healthy for the first few
weeks. In horses, no antibodies are passed through the placenta into the
fetus. The foal must be stomach-tubed with at least eight ounces of
milked-out colostrum (by a veterinarian) if more than five or six hours
passes without successful nursing. Note: A sterile large-sized horse
urinary catheter is ideal for this purpose.
2) Carefully observe the newly delivered foal to confirm that it passes
the first stools called meconium. These stools will be black and the foal
will strain as it eliminates them.
3) The new foal's stools should change to yellow within the next 12 hours,
indicating that it has now successfully processed the first of its
mother's milk. Diarrhea is always better than constipation at this crucial
4) Finally, some of the new foal's urine should be passed within four to
six hours. It should be almost clear, not:
-absent (perforated ureter?)
-dark yellow (dehydrated?)
-opaque (urinary tract infection?)
- or red (contains blood?).