A mesenteric tear as a cause of dystocia

 Keywords: dystocia. equine, mesentry, tear

A Belgium draft mare was referred to our clinic several hours after the onset of second stage parturition. Attempts by the rDVM to deliver the foal had been unsuccessful.

During per rectal examination to ascertain the presence of possible uterine torsion, the foal was not palpable yet one could easily palpate the foal via per vagina examination. This led to some confusion and speculation on the part of the author. Amid this discussion, the owners elected to euthanize the mare.

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On postmortem examination, a large rent was discovered in the mesentery. The large bowel and mesenteric rent is shown above. The location of the body of the uterus and fetus was simulated by the author. The smooth margins of the rent have not been re-touched in this image; they were exactly as shown here.

Evidently, the mesenteric rent had occurred some time before the mare had become pregnant or during early pregnancy, allowing the uterus and part of the mesometrium to pass through this opening. The foal had developed to term, cranial to the opening.  This explained why the foal could not be palpated per rectum yet was easily palpable per vagina. During per vagina examination, the author's arm had passed into the uterus, through the opening in the mesentery. During per rectal examination however, the large bowel lay between the rectum and uterus, disguising the presence of the fetus.

It was not possible for the foal to be born because it had been constrained by the hole in the mesentery. A unique case.

A salivary cyst as a cause of dystocia 

Keywords: salivary, cyst, equine,dystocia

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A very unusual case of dystocia, caused by a massive sub mandibular salivary cyst. Puncture and drainage of the cyst allowed delivery of the dead foal.

Premature placental separation (placenta previa) and prolapse of the bladder

Keywords: dystocia, premature, placenta, separation, equine

The term chorioallantois  is used more than three times as common as allantochorion in academic citations. Therefore it is used in preference to allantochorion in this entry.  The chorioallantois is the result of fusion of the chorion (the outermost fetal membrane in all mammals) and the outer surface of the allantois. 

At the onset of second stage parturition in all domestic animals, the chorioallantois normally ruptures where it overlies the internal cervical os. Allantoic fluid is released and the amnion appears at the vulva lips. 

During foaling, the bright red villous surface of the chorioallantois should not be seen until after the birth of the foal, when the placenta is expelled during third stage parturition. If it is seen at any time before the foal is born, the surfaces for gaseous exchange between fetus and dam (the endometrium and chorioallantois) are being separated, oxygen tension is lowered in the fetus and it is in danger of dying. A similar situation in humans is referred to as placenta previa (Latin praevius meaning previous) where the placenta lies over the cervix and precedes the birth of the fetus.  In humans however, the primary threat is life threatening hemorrhage, then anoxia. In horses the condition is commonly referred to as premature placental separation or colloquially, as "red bag" for obvious reasons. This author believes that the term placenta previa is also justified in mares because the placenta is being born before the fetus i.e. its appearance precedes that of the foal.  

The cervical canal is has no glands and does not participate in gaseous exchange. This may explain the avillous nature of the chorionic surface of the chorioallantois at this site i.e. the so-called "cervical star". The  avillous rays may develop from folding of the chorioallatois over the internal cervical os.

The image below is that of a five month pregnancy, removed from the uterus. The cervical star, covering the head of the foal, is particularly obvious.

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In the image below, the cervix has been opened at post mortem in a term equine pregnancy. The cervical canal is at the lower right of the image. A finger points to the white, avillous rays of the surface of the allantochorion that lie over the cervix. 

Although the cervical star is the most common site of chorioallatoic rupture, in normal foalings it may also rupture a short distance away.  

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The image below is that of a placenta from a term pregnancy. As is commonly the case, the placenta was found in the stall inside-out, with the allantoic surface of the chorioallantois showing and the chorionic surface inside the placenta.  For purposes of demonstration, the placenta was restored to its normal in-utero orientation, with the chorionic surface on the outside. A finger points to the site of rupture; in the center of the cervical star. The extra-amnionic umbilical cord lies within the site of rupture and the amnion is seen under the pointing  hand.

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As mentioned, premature placental separation is cause for an obstetrical  emergency.  If the chorioallantois protrudes from the vulva lips before the birth of the foal (as shown below) it should be transected immediately. This will release allantoic fluid. The translucent amnion will then be seen; the foal within. That membrane in turn should be transected and the foal delivered immediately.

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Images such as this are rare because the condition demands immediate attention, seldom allowing time for photography. The author of the image and holder of copyright is Dr Dale Paccamonti. pacc@lsu.edu

One should not confuse a prolapsed bladder with the chorioallantois.   In the case pictured at left, a Shire mare prolapsed her bladder before foaling. It is the bright, smooth and glistening structure protruding from her vulva lips. By contrast, the chorioallantois is dull and velvet-like.  This is a rare condition. The white membrane adjacent to the bladder is part of the amnion. Clenbuterol was used to suppress foaling and epidural anesthesia was used to facilitate replacement of the bladder. Then, using conventional methods, a live foal was delivered. Image size: 865 x 481px

Hydrocephalus as a cause of dystocia

Keywords: dystocia, equine, hydrocephalus

Hydrocephalus is not an unusual cause of dystocia due to fetal malformation.  In such cases it is likely that the bulbous shape of the head prevents normal distention of the cervix, resulting in dystocia.

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In this case hydrocephalus was be reduced by puncturing the cranium within the uterus  thereby allowing delivery of the foal (see inset). In other cases, fetotomy or cesarean section may be required.

Severe skeletal malformation a cause of dystocia

Keywords: dystocia, equine, mare, wryneck, wry-neck

A pluriparous mare presented for dystocia of several hours duration. The referring veterinarian reported the presence of "a severely deformed" foal that precluded normal delivery.

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An epidural was given and clenbuterol were administered IV.

The foal was in anterior longitudinally presentation and dorso left-ilial position (arrow). There was an obvious wry-neck. Wry-neck is permanent ossification of the neck in a flexed posture; apparently unique to the horse among domestic animals.  The head was also deformed. Initially, one gained the impression that there was also bilateral shoulder flexion with both forelimbs retained.

Using a fetotome, the head was removed uneventfully but when an attempt was made to locate the forelimbs, they appear to be absent.  Because of the absence of the forelimbs, uterine tone and an inability to rotate the foal into a dorso-sacral position, the foal was delivered by cesarean section.  Her recovery was uneventful.

Radiology showed that both the left and right scapulae were present but only the right forelimb was present. Also, the right forelimb was vestigial, about the thickness of a thumb and it was also rotated on its longitudinal axis, so that the hoof faced backward. There was severe scoliosis and the head of the left femur did not articulate with the acetabulum.

Equine dystocia

Keywords: equine, foaling, dystocia

In most cases of the equine dystocia, the foal dies quickly. In fact, the vast majority of foals involved in dystocia will be dead by the time the veterinarian arrives. This is because the equine placenta separates from the endometrium rapidly during foaling. This is distinctly different to the situation in cows where the majority of calves are still alive when mutation and traction are first attempted.

Epidural anesthesia is slow and unpredictable in mares and therefore of limited value in cases of dystocia. However, it can be used for fetotomy in standing restraint (when the fetus has died) because there is usually time to perform an epidural and wait for it to take effect. In fact, epidural anesthesia was used to relieve dystocia by fetotomy in the inset of the main image below. If an attempt at epidural anesthesia fails, it is useful to remember that brief periods of relief from straining can be obtained by pulling out the tongue of the mare. This makes it impossible for her to close her glottis and strain during attempts at mutation and traction.

Because sympathetic stimulation causes uterine relaxation, the beta 2 sympathetic agonist clenbuterol is an excellent tocolytic and should be used when possible.  However, it may not be used in countries where horse meat is used for human consumption. The use of clenbuterol may be banned in cattle for that reason as well.

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If a live foal cannot be delivered in 5 to 10 minutes, general anesthesia should be induced immediately. This provides restraint as well as excellent uterine relaxation. When the hind quarters are elevated, the foal also moves cranially providing space in the uterus for fetal mutation. Under farm conditions, the author is aware of dystocia that was relieved by raising the hind quarters of an anesthetized mare using a tractor with a front-end loader!

Under more sophisticated conditions, such as a hospital adjacent to a major breeding facility, an attempt at mutation and traction is made while the mare is prepared for a potential cesarean section. This saves time in the event that a cesarean section is required.

3264 x 2448 px. Image copyright of Dr R.M. Embertson. rembertson@roodandriddle.com

If delivery is not successful while the mare is being prepared for surgery (~ 10 to 15 minutes) one can immediately resort of surgery. In this manner, the majority of foals will be delivered live. Under field conditions, most will die before or during mutation and traction.

Severe skeletal malformation in a foal

Keywords: dystocia, equine, mare, radiograph, wryneck, fetus

A pluriparous Standardbred mare was presented for dystocia of several hours duration. The referring veterinarian reported the presence of "a severely deformed" foal that precluded normal delivery.

An epidural was given and the beta 2 agonist clenbuterol, was administered IV and the pregnancy was examined per vagina. 

A dead foal was in anterior longitudinally presentation and dorso left-ilial position. It had

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an obvious wry-neck. Wry-neck is permanent in-utero fixation of the neck in a flexed posture; unique to horses among domestic animals.  The head of the foal was also deformed. Initially, one gained the impression that there was bilateral shoulder flexion with both forelimbs retained. 

Using a fetotome, the head was removed uneventfully but when an attempt was made to locate the forelimbs, they appeared to be absent.  Because of the absence of the forelimbs, uterine tone and an inability to rotate the foal into a dorso-sacral position, the foal was delivered by cesarean section.  The mare's recovery was uneventful.

Radiology showed that both the left and right scapulae were present but only the right forelimb was present.

Image size: 2070 x 2295px

Also, the right forelimb was vestigial, about the thickness of a thumb and it was also rotated on its longitudinal axis, so that the hoof faced backward. There was severe scoliosis and the head of the left femur did not articulate with the acetabulum.