A model to explain foaling

Keywords: equine, education, model, foaling

Image size:1478 x 813 px

The author uses this model frequently, especially during the foaling season when students participate in foal watches and when owners require instructions on what to expect during foaling and when to intervene. The model can be used to demonstrate the diffuse nature of equine placentation and how readily this may detach from the endometrium in cases of dystocia; far more rapidly than in ruminants. They are informed that this (in large part) accounts for the high death rate in equine dystocia. It is emphasized that second stage foaling is also very rapid and that the foal is likely to die unless the first responder has basic knowledge of how to respond during foaling. This is why the teaching model has proven valuable and why the author encourages others to build similar models.

With an assistant holding the red velvet allantochorion stationary within an imaginary uterus, the author demonstrates how the allantochorion remains attached to the endometrium after it has ruptured at the site of the cervical star. At this point, the author usually digresses, showing how the allantochorion can become detached from the endometrium, even before it has ruptured at the cervical star. In that case, it would move caudally and appear at the vulva lips instead of the amnion. This  serves to introduce the subject of premature placental separation (red bag) and the importance of rapid intervention should that occur.

Progressing in the vein of a normal foaling, the author shows how the amnion appears at the vulva lips with the forelimbs and muzzle of the foal visible through the amnionic membrane. The translucent polyester material used for the model allows this to be demonstrated clearly. There is an elasticized opening in the amnion. This opening shows where an attendant would cut the amnion or where it would rupture spontaneously. The author notes the possibility of asphyxiation in foals caused by an intact amnion remaining over the foal's muzzle after birth and consequently, stresses the need to transect or rupture the amnion when it first appears at the vulva lips.

At this time (before the simulated second stage is complete) the author may pull the model apart so that it is clear that the umbilical cord has two distinct parts; the intra-amnionic cord and the extra-amnionic cord. It is emphasized that this anatomy is distinctly different from that in ruminants where the amnion is attached to the chorion and there is no extra-amnionic cord. Furthermore, the author continues, it is that difference in anatomy that prevents the amnion from leaving the vulva lips and suffocating the newborn ruminant. In horses by contrast, the amnion is shown (in the model) to be free of the chorion, tethered to it only by the extra-amnionic cord. This allows the amnion to be born without rupturing, making neonatal asphyxiation a significant reality in horses; hence the need for amnionic rupture by the attendant.

At this time as well, for students of veterinary medicine or animal science it is useful to show a major difference in the anatomy of the intra- and extra-amnionic umbilical cords i.e. the presence or absence of the urachus. In the model, a yellow-colored string on the intra-amnionic umbilical cord represents the urachus. The urachus is shown to leave the umbilical cord where leaves the amnion and emerges into the allantois. This is used to demonstrate how allantoic fluid (predominantly urine) accumulates within the allantoic cavity. If the model is re-assembled at this point, it is possible to demonstrated how the allantoic fluid escapes when the allantochorion ruptures at the cervical star. The author adds that this is the first major discharge of fluid that occurs during foaling; before the rupture of the amnion and the discharge of amnionic fluid.

With the model re-assembled and the elasticized opening of the amnion at the vulva lips, the author emphasizes the need for immediate examination of fetal presentation, position and posture. Noting those conditions under which foaling is unlikely to proceed without specialized assistance (wry-neck, shoulder flexion, breech posture etc), the author turns to basic obstetrical mutations, especially carpal flexion and the need to repel the foal to obtain space for mutation. With the current model, the stuffed toy has short limbs that make it difficult to demonstrate malposture. A longer limbed toy would be preferable.

With the toy foal in normal position and posture, one can suggest to the student or owner that with a live foal, this is a time when one could contemplate leaving the stall, to observe the completion of foaling from a distance. Alternatively, if progress appears to have stalled, to intervene as necessary.

Once the toy foal has been "delivered", it is easy to demonstrate how the placenta can be expelled inside out or in its normal anatomical situation. The author usually takes this opportunity to mention that the placenta should be kept for inspection to ensure that placental fragments have not been retained and that there are no signs of placental pathology. This is also a convenient time to introduce the idea of time limits for placental expulsion and suckling (~3 hours in both cases).

Having used this model for many years, the author can attest to its value in teaching students and preparing horses owners for foaling.

Mesometrial hemotoma causing peritonitis

Keywords: equine, hematoma, mesometrium, fatal, foaling, peritonitis

An unusual variation of a mesometrial hematoma caused by a ruptured uterine artery. 

In this case, the hematoma spread more caudally than is common. Eventually its contents seeped into the peritoneal cavity through the site marked by the forceps in this image. In addition, a small thread-like fistula existed between the caudal area of the cervix and the most caudal part of the hematoma. This fistula may have formed as a result of cervical laceration during foaling. A long blunt probe was passed through the fistula to reveal its location in this image.

Image size:1618 x 1240px

Several days after foaling, the mare developed severe acute peritonitis and died. It was concluded that infection had spread into the hematoma from the injury in the cervix (lowest red arrow), through the hematoma and into the peritoneal cavity (upper red arrow & forceps).

Because of the pressure required to dissect connective tissue and form this large hematoma, it was remarkable that blood had not burst into the peritoneal cavity at the time of foaling. Perhaps bleeding had been intermittent, allowing a degree of coagulation. This would have permitted the hematoma itself to act like a valve, preventing blood from entering the peritoneal cavity where the forceps are shown here. Also, there were no obvious signs of putrefaction in the blood clot although it was clearly the only source of infection for the peritonitis that ensued.  Cytology of the coagulum was not performed; an important omission in this case. In retrospect, it would probably have revealed many bacteria.

For consideration by clinicians: Routine examination of the mesometrium by ultrasonography immediately after foaling is seldom if ever done. The author is in favor of routine examination of the vagina after foaling to detect tears into the peritoneal cavity. However, some owners object to this practice on the basis that it could interfere with dam-offspring bonding. If an owner allows this, it may be good practice to examine the mesometrium and pelvis for hematomas at the same time. If a hematoma is detected via ultrasonography, one could consider prophylactic treatment with antibiotics and tetanus toxoid.

Rectal prolapse after trauma to the vagina during foaling

Keywords: foaling, trauma, rectum, prolapse, intussusception

A pony mare foaled approximately 48 hours before these photographs were taken. The foal (shown in the inset image) had hind-limb arthrogryposis and only lived for short time after birth.

Two hours after parturition, the mare's rectum prolapsed and was reinserted by an attending veterinarian. A circumferential retention suture was placed around the anus.  Shortly afterwards, the mare began to show signs of shock and severe pain. She was euthanized.

The top image shows how the end of the rectal intussusception has come to lie within the caudal part of the rectum. A finger has been inserted into the end of the intussusception. The anus is indicated by the yellow arrow. The vulva lips can be seen just below the tail of that arrow. U indicates the uterus. To assist one in understanding this image, a smaller color coded version has been created beneath it.

Image size: 1451 x 942px

Image size: 726 x 471px

In this color coded image, the section of rectum that contains the intussusception is colored red and the intussusception itself is colored blue. The wall of the unaffected rectum is colored yellow.

One presumes that the rectal intussusception was a sequel to a painful birth and straining, possibly because of trauma to the soft birth canal caused by the deformed fetus. However the uterus, cervix (green arrow) and vagina only showed the degree of contusion pictured below. Many would consider that to be consistent with normal foaling so the cause of straining remained uncertain.

Image size: 1468 x 1040px

Mesenteric hemorrhage associated with foaling

Keywords: hemorrhage, foaling, equine, mare, intestine

A mature Standardbred mare that died suddenly immediately after foaling.  Her mucous membranes were extremely pale upon presentation and postmortem examination revealed that she had suffered from an extensive intra-abdominal hemorrhage. Contrary to expectation, the hemorrhage did not arise from a rupture of the uterine artery (prev. middle uterine artery). Instead, hemorrhage originated from one of the major vessels in the spleno-colic ligament. Bleeding extended into the mesentry and peritoneal cavity.

Image size: 1500 x 1227px

Despite an adequate worming program on this stud farm, the presiding pathologist suggested the mare could have experienced verminous arteritis and by extension, arterial rupture because of hypertension during foaling. However, some doubt  has been leveled at that suggestion, based on the fact that verminous arteritis due to S. vulgaris is still well controlled by current anthelmintics and cases of arteritis are no longer common in this geographical area (N.E. Canada). Instead, it has been suggested that the trauma seen here may have been sustained by the foal during parturition. The accompanying review substantiates that idea.

Reference: 
Dolente, B.A. et al. 2005. Mares admitted to a referralhospital for postpartum emergencies: 163 cases (1992-2002). J.Vet.Emergency and Critical Care 15: 193-200

Third-degree perineal lacerations

Keywords: laceration, degree, mare, foaling, injury

First and second degree perineal lacerations are seldom of importance, the first being laceration of the vaginal mucosa and the second, laceration of the vaginal mucosa and the tissue between the vagina and rectum.

Third degree lacerations involve the vaginal mucosa, rectal mucosa, and the interposing tissue.  They may take the form of fistulas or more commonly, complete destruction of the perineal body. As mentioned in an entry on evisceration after foaling these accidents appear to be more common in maiden mares than pluriparous mares.  These old but valuable images illustrate the problem well.

In the top right inset of the image below, a third degree laceration is being examined several days after foaling. A large hematoma is present in the left wall of the vestibule and there is considerable fecal contamination over the lacerated tissue between the vagina and rectum.  These injuries are almost never fatal and hemorrhage is seldom severe because of the blunt nature of this trauma.

The author estimates that the main image was obtained perhaps ten days later, when the hematoma had resolved and secondary intention healing of the torn tissue was well underway.

Image size: 840 x 767px  Modified. Original copyright Dept. Theriogenology, ISU. Ames, Iowa.

Although the value of antibiotic treatment is debatable in these cases, immediately tetanus prophylaxis is suggested. Although there is some disagreement on when surgery should occur, the author suggests that one should resist the temptation to repair these injuries surgically until second intention healing is complete. If that is done, the wound margins and viable tissue can be clearly delineated for surgery.

In practice, the foal is also weaned before surgical repair is attempted because dietary restrictions imposed on the mare (to decrease fecal production) will retard the growth of the foal.

Owners may be concerned to wait for several month for repair because fecal contamination of the vagina continues during that period. Remarkably,this approach does not appear to have a detrimental effect on the future reproductive capacity of mares. This could be due to excellent uterine defense mechanisms in young mares,

Method of repair:

Image size: 743 x 824px  Modified. Original copyright Dept. Theriogenology, ISU. Ames, Iowa.

The author has used an Aanes two-stage technique modified by Dr. Tracy Clark at Iowa State University. The image at upper left shows how the perineum has been prepared for surgery. Pre-surgical starvation diminishes the amount of feces in the rectum (ringed in the lower left inset) at the time of surgery. After all feces have been removed by hand, fecal debris can be prevented from entering the surgical field by using a large tampon device made of rolled cotton, held together with half hitches of umbilical tape, complete with a tail of tape to withdraw it from the rectum after surgery.  Epidural anesthesia is used.

The inset image at lower right shows how the rectum, vagina and interposing tissue are repaired using a continuous, cranial-to-caudal suture pattern. No attempt is made to reconstruct the perineal body during first stage repair. Doing so will cause feces to exert pressure on the anus, breaking the suture line described above.

After the first stage has healed, the perineum is reconstructed.

Third degree lacerations of the perineal body may not involve the anus; after healing they take the form of  fistulas between the vagina and rectum. Sometimes these fistulas are large, allowing these animals to defecate through their vulva lips. Such a case is shown below.

Image size: 444 x 1050px  Modified. Original copyright Dept. Theriogenology, ISU. Ames, Iowa.

The lower image shows the area being prepared for surgery with a dramatic demonstration of the extent of the lesion to be repaired. The technique used is similar to the first stage described above.

Reference: 

Aanes, W.A. 1988. Surgical management of foaling injuries. Vet. Clin. North Am. Equine Pract. 4:417-438. 

Per rectal evisceration after foaling

Keywords: trauma, equine, mare, foaling, rectum

The first image shows a six year old mare presented shortly after her first foaling.  Despite video surveillance, foaling was rapid and consequently, unattended. The birth of a live foal was followed immediately by evisceration from the anus. As shown in inset A, a temporary purse string suture had been placed around the anus by the rDVM.

Image size: 990 x 747px

When the purse string was released, intestines burst out of the anus as shown in inset B. The placenta remained hanging from the vulva lips. The intestines had passed out of the peritoneal cavity through a tear in the rectum. Blood on the operator's glove after detection of the rectal tear:

Image size: 800 x 600px

The injury to the rectum was not caused by the foal because neither the uterus nor the vagina were damaged. This defies a simple explanation. It is possible that the rectum may have ruptured due to high abdominal pressure during foaling but the author is not aware of previous reports of such an accident. The mare was euthanized

More commonly evisceration occurs through vaginal tears.  The image below show how viscera can escape through the vagina. Note that the cervix and even the cranial vagina lie well within the peritoneal cavity, cranial to the reflection of the peritoneum in the recto-genital pouch. This anatomy makes it possible to perform ovariectomy via colpotomy in both mares and cows. However it becomes a potential liability in mares during foaling. This is because foaling is far  rapid than calving and a foal's forelimbs are more likely to traumatize the cranial vagina than is the case for calves. This is especially so if the foal is in foot-nape posture during second stage. If the foal’s hooves penetrate the vagina where it lies within the peritoneal cavity, intestines can enter the vagina through the site of penetration.

The image below clarifies this. LUH and RUH are the left and right uterine horns. PR is the peritoneal refection, edged by a red line, in the recto-genital pouch. The green lines show the cranial and caudal extents of the cervix. The red arrow points to a common site of vaginal penetration, the roof of the cranial vagina. The curved yellow arrow shows how intestines can move into the vagina. The rectum can be seen as a shaded body above the genital tract.

1232 x 919px

In the image below, a foal's legs penetrated the cranial vagina, entering the recto-genital fossa. This allowed the intestines (yellow arrow) including the large colon, to escape from the peritoneal cavity. Such cases are invariably fatal.

Image size: 1200 x 1008px Copyright Dept. Theriogenology, ISU. Ames, Iowa.

It is important to note that evisceration may occur some time after the birth of the foal, when the mare lies down and pressure is exerted on the abdomen. Evisceration through tears in the uterus is also possible, through the open cervix. Both vaginal and uterine tears can be present in mares that appear to be totally normal.  Although some owners object to potential interference with dam-offspring bonding immediately after foaling, the author always requests permission to examine the cranial vagina and uterus (as far cranial as possible) at that time.

The reader should be aware that it is far more common for a foal's hooves to tear through the caudal part of the vagina than the cranial part of the vagina. Tears often occur through the dorsal wall of the vestibule and there may even be total ablation of the perineal body. In those cases there is no danger of evisceration.

Note: Foaling accidents appear to be more common in maiden mares than pluriparous mares. This may be because the tract is smaller and less distensible in younger, than older animals. Also, maiden mares may panic and strain excessively during this novel experience. 

Severe iatrogenic trauma during foaling.

Keywords: iatrogenic, foaling, trauma, equine

A nine year old Standardbred mare had an assisted foaling because of an apparent "hip lock". This was regarded by the author with circumspect because hip lock is rare in mares due to their large pelvic sizes compared to cattle*. It is perhaps more likely that the foal had unilateral or bilateral hock flexion i.e. "dog sitting" posture:

Image size: 805 x 492 px. Source unknown; contact lofstedt@upei.ca to verify copyright.

Either of these postural abnormalities may have been resolved partially or completely during traction. The nature of assistance was unclear but non-human mechanical forces may have been involved.

Image size: 1492 x 2088px

A live foal was extracted. However, the mare appeared to be partially paralyzed in her hind quarters and was unable to rise.  Her heart rate was elevated at 80 beats per minute and later rose to 130 beats per minute despite treatment with an NSAID and fluids.  The mares packed cell volume was 37% but may have remained high because of splenic contraction.  Hemorrhage from the vulva lips was obvious, soaking the adjacent pasture (see inset).  The owner elected to euthanize the mare.

The lower image shows some of the postmortem findings; extensive muscular and fibrous tissue necrosis within the vaginal wall. There was also subluxation of the mare's right sacroiliac joint. Severe coalescing vaginal and vulvar hematomas were also present.

Note: It is essential to determine the presentation, posture and position of a foal before traction is attempted. The foal should be repelled and posture should be corrected, preferably with copious lubrication. In most cases (unlike calves) the foal will be dead in prolonged cases of dystocia. It is difficult to repel a foal to correct malposture because epidural anesthesia is either unavailable or slow to take effect. In such cases, pulling out the mare's tongue will prevent closure of her epiglottis. Perhaps obviously, this will have no effect on myometrial contraction but will prevent the mare from straining voluntarily. This information is valuable to clients with pregnant mares because they will often provide assistance in foaling before the veterinarian arrives at the farm.

*The birth canal in a mature mare has a cross-sectional area of about 400 square cm; a cow about 280 square cm.

Contusion of the vestibule

Keywords: contusion, vestibule, foaling, equine

Even during normal foaling, there is frequently a degree of contusion of the vagina. This illustration shows contusion in the vestibule that is consistent with normal foaling.

Image size: 1200 x 2000px

Optimally, one should perform a gloved hand examination of the vagina after every foaling, in the event that serious vaginal damage has occurred.

Note: The vestibule is that portion of the vagina that lies between the vulva lips and the external urethral opening.

Hydrops

Keywords: hydrops, equine, foaling, induction

A 17-year-old Standardbred mare was presented for signs of abdominal discomfort, anorexia and a possible ventral rupture (erroneously referred to as "rupture of the pre-pubic tendon"; see this LORI entry). This mare was due to foal approximately 2 weeks after the time of presentation. The referring veterinarian reported rapid abdominal enlargement over the two week period before presentation.

The uterus was distended with fluid and a live fetus could be detected by ballottement per rectum. In a single day after admission, this mare gained 10 kg in weight, strongly suggesting some form of hydrops.

Image size: 1050  x 1593px

In the image, abdominal enlargement and ventral edema is indicated by a red arrow. Because of the potential for ventral rupture, foaling was introduced using oxytocin.  Milk electrolyte changes were used to determine the optimal time for induction. At the onset of second stage, it was noted that the chorioallantois was abnormally thickened. It was transected and a small, live filly foal was delivered in caudal presentation.

It was estimated that approximately 100 L of fluid had been released when the placenta was transected. The mare weighed 710 kg on admission and 570 kg immediately after foaling. The placental weight was 15 kg (approximately double its normal weight) and her foal weighed 30 kg. Therefore, the fluid content of the placenta was 90 kg or 90 liters. The normal amount of allantoic fluid normally varies from 8 to 15 L1 and the amnionic fluid somewhat less. Therefore there was little doubt that this mare had experienced hydrops allantois. However, the possibility of additional hydrops amnion component could not be excluded.

Shortly after foaling the mare experienced severe hypovolemic shock requiring aggressive fluid therapy. Due to continuing pain and damage of ventral abdominal structures that would probably compromise future pregnancies, the mare was euthanized at the request of the owner.

Notes: Both hydrops allantois and hydrops amnion are rare in mares. Although one is said to be more common that the other, neither can be dismissed on rates of probability when a mare is presented. Also, these condition are so sporadic that their etiology has not been properly studied.  Hydrops of either type can be diagnosed by sudden changes in weight, girth size and the ultrasonographic appearance of fetal fluids. Also, the biochemistry of the fetal fluids can be used to differentiate between hydrops in either compartment.

A major challenge in the case management of hydrops is to stabilize the mare after large amounts of fluids have been lost from the abdomen. Although this fluid is not lost from the blood stream, this author suggests that the sudden decrease in abdominal pressure may cause pooling of blood in the abdominal vessels, vascular dilation and following laplace's law, fluid loss into the peritoneal cavity

 References:

Arthur, C.H. 1975. Veterinary reproduction and obstetrics.  Fourth edition, London, Balliere Tindall. 41-42

Blanchard, T.L. et al. 1987. Hydroallantois in two mares. Equine Vet J. 222-225

Christensen, B.W. et al. 2006. Management of hydrops amnion in a mare resulting in birth of a live foal. J. Am. Vet. Med.Assoc.228:1228–1233

Honnas, C.M. et al 1988. Hydramnios causing uterine rupture in a mare. J.Am.Vet.Med.Assoc. 193:334-336

Normal edema at term and ventral rupture

Keywords: ventral, edema, rupture, equine, mare, foaling, pain

The plaque of ventral edema shown below (arrows) is typical of late gestation in mares.

Image size: 1200 x 890 px

The affected area pits on pressure but the mare shows no discomfort at all. This makes this condition very different from impending rupture of the ventral abdominal structures.  That condition is shown below.

Impending rupture of ventral abdominal structures during late gestation.

A massive ventral plaque of edema (more obvious than the usual ventral edema of late gestation) and the painful gait of the mare are indicators of this condition. As shown in inset A, ventral edema may be so severe that the architecture of the mammary gland is largely obscured. Severe edema is also illustrated at lower left where the margin between the plaque of edema and the ventral abdomen is indicated by red arrows.

Image size: 1500 x 2102 px

Monitoring of milk electrolytes should be used to decide when to induce foaling. If the mare is off site, milk for electrolyte analysis can be collected by the owner. Assistance may be required during foaling. It has been suggested that minimal intervention is perhaps better that induction of foaling but that decision depends on prevailing conditions. In other words, if the mare is at a referral institution where 24 hour monitoring is possible, it may not be advisable to induce foaling. That is because induction of foaling is potentially hazardous, especially if it is done prematurely. In such cases, one would expect a higher incidence of failure of passive transfer and because the foal is not mature, a higher incidence of dystocia as well (movement into the correct position and posture is largely a function of fetal maturity).

After foaling, ventral edema usually subsides quickly enough to allow suckling (inset B). Otherwise, plasma transfusions may be given to prevent failure of passive transfer in the foal

If possible, the mare's abdomen should be supported until she can be induced to provide a viable foal. Supports can be made from wide elastic bandage i.e. Elastoplast TM, or a similar adhesive or partially adhesive bandage. Alternatively, a custom made support system can be used, such as that shown here.

Image size: 1200 x 1000px. Copyright Dr G. Colbern.  gtcolbern@gmail.com

Although the condition is often referred to as "rupture of the prepubic tendon" antemortem examination using ultrasound and posrtmorten examination in euthanized mares has shown that rupture may involve the prepubic tendon, the rectus abdominus muscle, the transverse abdominal muscles or oblique abdominal muscles.

Surgical reconstruction of the abdomen has been described but the long term success of those cases as broodmares is not known.  Soon after foaling, damage to abdominal is no longer visible so it may be tempting to re-breed these mares. This is not recommended because the condition is known to  reoccur in subsequent pregnancies.

References:

Blanchard, T.L. et al. 1987. Hydroallantois in two mares. Equine Vet J. 222-225

Ross, J et al. 2008. Body wall tears during late pregnancy in mares: 13 cases (1995–2006) J Am Vet Med Assoc. 232:257–261

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.

Image size 1650 x 946 px.

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.

Lactation and foaling

Keywords: milk, electrolytes, pH, foaling, equine

The first evidence that foaling is about to occur is a sudden and remarkable increase in filling of the mammary gland. In the illustration below, there is a remarkable difference between the mammary gland in the inset (approximately 1 week before foaling) and the mammary gland in the main image, one day prior to foaling. The larger inset serves as reminder that milk electrolyte or pH monitoring should begin when sudden enlargement of the mammary gland is noticed. Sampling is usually done once a day, usually in the evening.

Image size: 1500 x 1880px

Sodium (and chloride) milk in colostrum decrease with the approach of foaling. At the same time, potassium and calcium concentrations rise. However, of the three electrolytes in question, it is calcium that shows the most acute change as foaling approaches. Around foaling, calcium concentrations are about ten times higher than those in blood. Therefore colostral calcium concentrations have been used for many years to indicate when foaling may occur.

Water hardness test strips as well as commercial tests are base on calcium concentrations but high calcium concentration alone are not highly correlated to the time of foaling. As a result, these tests are best suited as negative tests for foaling i.e. to indicate that foaling is unlikely to occur.
The image below shows the results of a common water hardness test superimposed on a graph of milk electrolytes.

Image size: 659 x 802px

When the concentrations of  calcium, sodium and potassium are combined, one is afforded a better prediction of foaling than with calcium alone. A chart such as that shown here can be used to predict the spontaneous time of foaling and if necessary, when it is safe to induce foaling.

Image size:1597 x 1110px

The pH of milk has been examined and compared to milk electrolytes for its value in predicting the time of foaling. In preliminary observations, it appears that the pH of milk is significantly correlated to changes in milk electrolytes and may also be used to predict foaling. It is not clear at this time if pH is superior to milk electrolytes to predict foaling. It is however, very simple to determine pH and even pH test strips are sufficiently accurate for this purpose. Sampling is also done once per day, preferably in the evening. The reason for a drop in pH with the approach of foaling is not clear.

In the image below. the pH of milk is compared to the time of foaling, superimposed on a graph of milk electrolytes. The greenish bar indicates the approach of foaling.

Image size: 1560 x 18545px

Image size: 500 x 397 px.

Colostrum also starts to become opaque (above) shortly before foaling because of an increase in content of kappa casein. This has also been used as an indicator of impending foaling. However little data exists on the accuracy of this observation. It is certainly not reliable in the hands of this author.

Note: "Waxing" (the accumulation of dried colostrum on teat tips) is often mentioned as a harbinger of foaling but many mares never show obvious waxing.

A note on the induction of foaling. One should not induce foaling in the absence of proof of readiness because premature foals are likely to experience malposture and neonatal respiratory embarrassment. Also, immunoglobulins increase in the mammary gland at an almost logarithmic rate as foaling approaches. Therefore a few days short of the natural duration of pregnancy may translate into a significant deficiency of immunoglobulins in the colostrum. For that reason and because of gut immaturity in the foal, failure of passive transfer is common when foaling is induced. One must only induce foaling when spontaneous foaling itself in imminent. Estimating the time of normal foaling can be difficult. This is important from the point of view of routine monitoring of foaling. It is however, absolutely critical when one induces foaling for conditions such as neonatal isoerythrolysis, ventral abdominal ruptures, orthopedic injuries etc. Again, one should let a mare foal spontaneously if at all possible; foal survival rates are not only higher than otherwise but should a complication arise, it is readily interpreted as veterinary malpractice.

References: 

Canisso, I.F. et al. 2013 Decreasing pH of mammary gland secretions is associated with parturition and is correlated with electrolyte concentrations in prefoaling mares. Vet. Record 173:218. Online ISSN 2042-7670

Ousey, J.C. et al.1984.  Preliminary studies  of  mammary secretions  in the mare to assess foetal readiness for birth. Equine  vet. J. 16: 259-263

Trans-luminal adhesions

Keywords: foaling, injury, obstetrics, adhesions

Purulent discharge seen on the floor (red ellipse) behind a mare. This mare discharged pus intermittently because of multiple draining abscesses that had formed in her vagina. These abscesses formed between trans-luminal adhesions caused by vaginal irritation. This followed prolonged intervention during dystocia.  This also caused obliteration of the cervix.

Image size: 2240 x 1606px

This illustration also shows how the extent of trans-luminal adhesions can be evaluated using transrectal ultrasonography and an infusion of saline.  At the upper right corner, a green check mark shows the normal appearance of saline in a uterine lumen.  Its echogenicity is due to microscopic bubbles of air that are normally found in saline. This appearance makes saline an ideal contrast medium for the evaluation of the uterine and vaginal integrity using ultrasound.

In the red rectangle, one can see how poorly an infusion of saline had distributed itself within the uterine lumen of another mare. That mare had severe trans-luminal adhesions throughout her uterus, probably as a result of a foaling injury.

Trans-luminal vaginal adhesions arising from the management of dystocia are not uncommon. To prevent trans-luminal adhesions from forming, a lubricating substance such as oil-based mastitis ointment can be applied to the vaginal wall two or three times at 48 hrs intervals after relieving an equine dystocias. Similar adhesions are rare in other species following treatment for dystocia; the equine vaginal wall appears to be especially sensitive to abrasion and chemical irritation.