Managing dystocia in mares (Proceedings)

Context

Foaling problems are very stressful for most practitioners, mares, and horse owners. The maternal and fetal outcomes during dystocia are less successful for the mare compared to other species. An understanding of the underlying causes and strategies to remedy dystocia are essential for a successful outcome.

In this paper we will discuss normal parturition, the main causes of dystocia, the signs of dystocia, the time frames for intervention, the decision process, and principles, options, and remedies for dystocia in the mare.

Parturition is characterized by fetal hypothalamo-pituitary- adrenal placental maturation and cross talk with the dam that signals the readiness, for birth and sets in motion the accompanying changes that prepare the dam for birth of the foal. Fetal maturation results in fetal adrenal activation to prepare the fetus for birth including final organ maturation such as the production of surfactant in the lung, initiation of lactation, and a shifting steroid ratio which sets up the cascade of events that leads to relaxation of the pelvic ligaments, softening of the cervix, preparation of the birth canal, and labour - like contractions.

Greater than 90% of all foaling occur without any needed intervention. When intervention is needed however the life of the mare and the foal often hang in the balance. Pregnancy and parturition are a risky business for mares. Risk adverse clients should not breed their mares!

A key to a successful outcome during difficult times is preparedness, and if trouble arises a plan needs to be in place to handle trouble. Practice seminars and educational materials are helpful tools, and networking occasions.

Veterinarians should know these time frames for normal parturition

     • Stage I - Coordinated forceful uterine contractions, begin slowly and in total likely last around 14 hours. The last 4 hours usually corresponds to cervical dilation. This is when labour is obviously underway and the contractions are frequent. The mare shows typical colicky – like behaviour. Violent colicky behaviour is not normal.

     • Stage II - Rupture of the Chorioallantois and delivery of the fetus (5 - 30 minutes). The rupture of the chorioallantois (water breaking) occurs usually without the mare posturing as if to urinate. As she gets up and down this fluid will continue to leak out. It will appear to like urine. At this stage it is important to watch for trouble: premature separation of the placenta (Red bag) where the chorioallantois does not rupture, requires immediate intervention. Failure to progress so the fetal limbs are visible 30 minutes after the chorioallantoic membrane has ruptured ( water has broken), or malpositioning of fetus when something is presented at the vulva that should not be there. Normally the bluish amnion is presented and 2 feet 10 cm apart and a nose are visible.

     • Stage III - Passage of the placenta (< 4 hours), may be as soon as 10 minutes, but within 2 hours. Begin treatment with oxytocin at 4 hours.

The main causes of dystocia include both Maternal and Fetal causes

Maternal causes include small or malformed birth canal such as might occur following pelvic fracture or injury;

Uterine inertia or fatigue: Primary versus Secondary, Older mares, hydropic conditions (excess birth fluid); Twinning: Both fetuses coming at once, often one or both are dead, most abort at 8 - 11 months; Uterine torsion: May or may not involve the cervix, a torsion may occur anytime from midgestation on, and the mare will usually present with colic-like signs; Ascending Uterine Infection: usually results in premature delivery of a weak small foal.

Fetal causes include:Fetal Malpositioning: carpal flexion most common; Fetal Oversize: Rare in horses; Fetal Monster or Malformation: Hydrocephalus, Contracted Foal Syndrome, Schistosomas refelxus

Signs of dystocia include: violent colic like signs in the mare, failure of the labour to progress to delivery of the foal, abnormal vaginal discharge, depression of the mare, excessive abdominal enlargement, abnormal membranes (chorioallantoic membrane) presenting at the vulva, abnormal fetal parts presenting at the vulva, inability of the foal to be pulled out, prolapsed rectum.

Violent-colic like signs

Foaling in mares is a physically demanding process. Mares that are showing signs of colic, violent rolling etc are believed to be trying to move in such a way to reposition the foal for delivery.

Failure of labour to progress

In these cases the labour starts and then either,chorioallantoic membrane fails to rupture (water breaks), or it breaks and nothing happens. These mares tend to act restless. They act like they are in labour but the contractions seem to stay at a low level. This may happen when the foal is in posterior presentation and the mare never really gets stimulated to strain to deliver the foal. Mares that are exhausted may be in this condition when they present.

Abnormal vaginal discharge

If placentitis is present or chronic separation of the placental membranes has occurred, an abnormal vaginal discharge will often be present. In terms of vaginal discharge only scant clear mucus with a slight blood tinge is normal in mares. Brown coloured or pus filled discharge is abnormal. Fetal fluids have a very characteristic odour, and are not foul smelling.

Depression

Depression of the mare may signal the mare is in trouble. Most mares in labour walk more and spend more time eating, as if to distract themselves. Mares should separate themselves from the group for labour, but they should be BAR. Best to perform a TPR on these, check for vaginal discharge or fluid coming from the vagina, and vulvar relaxation.

Excessive enlargement of the abdomen may mean a mare has a lot of physiological edema, which will be non-painful and not hot. The edema may be pitting. In some mares the edema is abnormal it is hot and the underlying muscles are painful. In these mares the body wall muscles have been compromised. Twins and hydropic conditions of the membranes may result in abdominal enlargement with or without body wall compromise.

Abnormal membranes presenting at the vulva

Only the opaque bluish amnion should present at the vulva during parturition. When the chorioallantoic membrane ruptures (water breaks) the allantoic fluid that looks like urine, will come in a gush from the vagina, and then will dribble out as the mare moves. Following the rupture of the chorioallantoic membranes at the cervical star a bluish opaque membrane with the foals' forelimbs visible in it will be seen coming out of the vagina. A serious condition called a red bag occurs when the chorioallantoic membrane fails to break as the cervix dilates. The chorioallanotic (CA) rather than rupturing progressively peels or separates prematurely separates from the uterus and is pushed into the vagina and out the vulva of the mare by uterine contractions. The chorioallantois is needed during delivery because it is the exchange surface for oxygen during birth. Separation of the membrane results in life threatening fetal asphyxia. A red bag requires immediate intervention. Because the chorioallantois should have ruptured at the cervix but fails to during premature separation of the placenta, the cervical star is prominent and visible as a white jagged star shaped area on the unruptured surface of red chorioallantoic membrane. Rupture the chorioallantoic membrane, and you will find the amniotic sac with the foal inside it. Break the amnion open and immediately assist the delivery of the foal. Most of these foals will develop neonatal maladjustment syndrome later after birth, even if they appear normal at birth due to the intrapartum asphyxia.

Abnormal parts presenting at the vulva

In a normal anterior presentation the soles of the foal's hooves should point ventrally down toward the ground. There should be 2 forelimbs coming spaced about 4 inches apart with the nose just behind it. Anything else coming from the vulva such as a head only, or if the soles of the hooves point dorsally either the fetus is upside down (anterior dorsopubic) or it is the hind feet coming. In a fetus that is a schistosomas the foal's abdominal contents may come out the vulva, or all 4 legs. Larger loops of bowel are the mare's, which signals a life threatening rupture is present.

Inability to deliver the foal There are some cases of fetal over size where traction will not deliver the foal. In fact the head and limbs may not fit into the mare's pelvis, or the foal becomes hip locked during the delivery. There are also certain maldispositions of foals that may lead to the inability to pull the foal. Positions, such as poll lock where the nose has not entered the pelvis, or dog sitting, where the front end of the foal is out, and the foal's hind limbs are hung up on the mare's pelvis. Contracted foals where the limbs are ankylosed and not able to be straitened to enter the birth canal are another cause. Other fetal monsters will also not allow delivery.

Rectal prolapse is a serious condition in mares. Mares that delivery only the head of the foal tend to strain excessively, and may then prolapse their rectum. Excessive traction in assisting a foaling, or in cases where there is maldisposition of the foal will lead to rectal prolapse. In situations where it is a tight fit, allowing the mare some time to stretch before the final pull, giving her a break and also sedating her more so she is less aware of what is happening may help. Rectal prolapsed of greater than 4 inches (10 cm) carries that risk that the mesocolic aretery of the horse will tear. The mesocolic artery is the sole blood supply to the caudal portion of the reproductive tract, rupture will result in progressive necrosis of the rectum which will result in loss of the mare due to peritonitis and inability to defecate. Occasionally a fetal extractor is needed to assist with delivery of a foal, these devices must be used with extreme caution as they may fatally damage a mare. The mare must be recumbent when they are applied and excessive force must be avoided.

Approach to the equine dystocia

It is very important that the mare is in safe working area. One of your first tasks is to keep everyone calm. Remove people from the working area who are hysteric or abusive.

Some Time Frames to remember, more than 4 hours of active labour and no progress, more than 30 minutes after the chorioallantois ruptures, or any of the above signs should trigger a veterinary examination

Key principles to remember in a mare dystocia is that:

     1. Absolute fetal oversize is very uncommon, therefore correction of the problem will usually allow you to pull the equine fetus.

     2. The actions of the dam must not be counterproductive to your efforts. The average mare outweighs the average vet by 450kg.

     3. Gravity must be your friend – get a recumbent mare up, point the mare down hill, or half unload the mare off the trailer so the front end is headed down hill

Begin with informed consent. Then perform a quick physical including TPR and assessment of hydration status and mucus membrane colour and refill time. Dystocic mares typical HR 80, increased RR, sweating, hemoconcentrated, stress leukogram. Perform QAT's if possible. Rule out hemorrhage, shock, peritonitis, endotoxemia. If you suspect peritonitis obtain abdominal fluid asap. Note that normal abdominal fluid may appear bloody in some normal mares at parturition and therefore abdominal fluid should have a laboratory evaluation before determining the significance of it (i.e. to confirm that the mare has peritonitis). Wrap the mare's tail. Emphasize safety and work where there is space and good footing. The mare does not tolerate as much uterine contamination and vaginal manipulation when compared to other species. Be clean, efficient, and as gentle as possible.

Next

Empty rectum this allows you to check for parts misplaced into the rectum, remove the manure that will soil your working area, and ascertain the presentation. Scrub the mare's perineum and SEDATE the mare (this will ALMOST always be needed see below), you may wish to put in a short catheter. Prepare for a vaginal examination.

The decision process means evaluating

     1. The Cervical Status (dilated or not). If the cervix is fully dilated you will not be able to find any of it. The vagina and uterus form one runway to the vulva. If the cervix is not fully dilated the mare be early in labour, or the mare may be exhausted and late in the labour as the cervix is now closing. If the cervix is twisted or spiralling the mare has a uterine torsion that involves the cervix. If the cervix is partially dilated, does mild traction result in rapid complete cervical dilation? This usually happens in the mare, it does not happen in the cow

     2. The Placental status (detached or not, detached usually means a dead fetus), If the red chorioallantois is coming from the vulva you likely have a highly compromised or non-vital foal. Alternatively the mare may have already foaled and she is passing her placenta.

     3. The Fetal status (alive or not) is determined by smell and condition of the fluids and fetus, palpation for reflex movement (eyeball retraction, blink reflex, suck reflex, pharyngeal reaction, pinch reflex, umbilical cord or chest palpation for heart beat, anal tone). Please note in cases of placentitis the fetal fluids may be highly abnormal and the fetus may still be viable. In most situations it is best to focus on the survival of the mare, as in a rural practice and many referral practices long response times make it difficult to get a live foal. Generally a mare may live to have another foal.

If fetus is alive 3 options to proceed

FIRST prepare to resuscitate foal (epinephrine, doxapram, suction, and oxygen)

1. Mutation

(Controlled vaginal delivery) mare is left standing and the fetus is repositioned, I generally do not advise wasting time without sedating the mare, all of your manipulations will take less time and be less traumatic.

The mare is sedated with (dormosedan; 2 - 10 mg (0.004 - 0.02 mg/kg) IV and butorphanol; 10mg IV (0.02 mg/kg TO EFFECT). The mare should be totally unaware of what you are doing back there, if she is turning to look at you, or walking away, or straining against you give her another 0.2ml of each. Keep on giving the 0.2ml as needed to keep her heavily sedated. Work on the sedated mare no more than 15 minutes then decide to go to #2 if not making any progress, or refer for #3 particularly if the fetus is over size.

Recommend using based on 500 kg horse: Clenbuterol; 10cc IV (0.6 micrograms / kg) if it is available to relax the uterus. If the uterus must be relaxed 10cc of 1/1000 epinephrine diluted into 60 mls total volume and injected slowly IV will also work.

Palpate the limbs and the joints. Flex the fetlock and limb. Position one hand on the fetlock and one hand up on the limb at the suspected hock or carpus. Flexion of a forelimb results in the fetlock and carpus bending in the same direction like an arc. Flexion of a hind limb results in the fetlock going one way and hock going the other way. If you think you have a hind leg go looking for the tail for conformation.

Pros and cons of epidurals

They take time to work, time that the foal does not usually have. You need a Local skin block at the sacrococcygeal site, then use 2 inch 18 or 20g needle (preferred). Beware that the tail desensitizes much sooner than the rest of the horse because it is lower and anesthetic agent gets there faster, and the anesthetic agent may take up to 20 minutes to diffuse cranially and have its effect on the perineum and vagina). Therefore caudal epidural is seldom used with a live foal. Epidural is usually Lidocaine 4cc with saline added to inject a 10cc volume, or 75 mg xylazine in 10cc saline (xylazine lasts longer than lidocaine), or the 2 combined.

2. Rapid assisted delivery

It is an alternative non-surgical method to reposition the fetus. This method involves general anesthesia and elevating the mare's hind quarters. Mare may already have detomidine and butorphanol (aka torb) on board, if she is still sedated then only ketamine is needed. If she is not sedated use Xylazine (1 mg/kg) sedation and Ketamine induction (2 mg/kg), may then intubate and go to gas if available or needed. Usually either you can fix it right away or not after you elevate the mare's hind quarters. If not may wish to have a superdrip ready. The mare's hind quarters are elevated so gravity is your friend, cleanse vulva, lubricate, mutate, place chains, put mare back down in lateral and perform the extraction or go to #3. After fetal delivery lavage the uterus to remove the lubricant, and give oxytocin. Provide good footing for recovery. Beware of LUBE coming from the mare's repro tract during recovery. It is a hazard. Remember to try to remove it before she wakes up or clean it up as it comes out!!!! or else risk limbs fractures of your patient while she slips on the lube trying to get up. If money is a problem or referral is not an option then euthanasia is sometimes performed if this technique does not resolve the problem.

Here is where preparedness comes in for a dystocia: transportation available, bobcat, tractor with front end loader, local arena, truck with a rope over a beam or a large tree branch, hoist in a clinic etc. in other words a plan to lift up the mare's back end if required. Plus a Phoning tree for trouble.

3. C-section

C-section is usually not the first choice for horses, horses are not humans! The complications following C-section are much greater with horses compared with humans and the surgery is very different and the surgery time is much longer. The biology of the horse means that anesthesia is much more problematic than in humans (1 in 1,000 don't recover). In many owners minds however they think of their own experiences which in human medicine means right to C-section. Due to the high cost of this surgical procedure, Cesarian section is reserved for the dystocias where the foal is typically viable and it cannot be repositioned for delivery, or the pelvis has sustained an injury so the foal cannot be delivered (elective C-section), or fetotomy cannot be accomplished safely. Unfortunately one of the reasons a skilled obstetrician cannot reposition a foal, is a fetal anomaly.

C-section is performed under general anesthesia is used and a ventral midline approach is used. Getting a horse under general anesthesia and ventilated is a big deal. The large colon of the horse is often in the way and needs to be repositioned. The surgeon must prevent any lubricant from entering the mare's abdomen, with as little as 60cc causing death in mares. The uterus must be carefully positioned and packed off before opening it. It is hard to move the uterus into the operating field. The cut uterus bleeds profusely. A contaminated uterus lowers the chance of the mare's survival because of increased risk of peritonitis. The placenta is removed from the edge and the cut edge of the uterus is often whip-stitched (simple continuous) for hemostasis prior to closure. Ileus is also common. Partial retention of fetal membranes is common as some of it may be inadvertently sewn into the closure. C-section may be required for fetal monsters.

A terminal cesarian section is sometimes performed to save the life of the foal. This is most common when the mare is of advanced age, has other medical problems such as colic and a c-section is needed to get a live foal. The mare is induced with either xylazine / ketamine or barbiturate, or she may be captive bolted, or shot in the brain (I prefer a 22 caliber). Medically a shot to the brain will induce unconsiousness and often the heart beat persists for some time. The foal is then removed from the mare and resuscitated. Owners must be prepared to handle an orphan. Foal is then resuscitated and it may be born anesthetized.

Be prepared to resuscitate the foal. Generally recommend tubing colostrum into any foals that are not normally – delivered, covering them with broad spectrum antibiotics, evacuating the meconium, watching for normal behaviour, and determining the foal's IgG. At 12 hours post-partum.

If the fetus is dead

Usually mutation or fetotomy is used to extract a dead fetus. Generally the fetus will die within a half hour of trying to reposition it. Many are presented dead.

Generally the mare is evaluated first by rectal exam, then the tail wrapped and perineum cleansed. The mare is usually then sedated as above and is given ± Clenbuterol (if available) and epidural as described above. Lubrication is added to distend the uterus. Mutation is attempted. If unsuccessful then either go to #2 above (rapid assisted delivery) or if the cervix is wide open then perform a partial fetotomy. If a full fetotomy is needed then it is best to refer the mare. The cervix must be wide open to attempt a fetotomy. Amputation of the head or one limb is often all that is needed. The head may be chained, pulled out the back of the sedated mare, and removed using a scalpel blade at the atlanto-occipital joint. The remainder of the fetus is retropulsed and repositioned for delivery. With the head gone the manipulations are much easier. Following removal of the fetus lavage the uterus until clean and give oxytocin to encourage involution. Monitor for toxemia and retained placenta-laminitis. Follow for a few days post partum to monitor for involution and fluid accumulation. The uterus will be 1.5x its non-pregnant size within 12 hours of parturition if it is involuting normally.

Specific conditions

Upside down fetuses (Anterior dorsopubic or dorsoabdominal fetuses) are found in:

     1. Abortion or premature delivery when the uterus is not contracting normally and fetus is not stimulated to attain the correct "diver like" orientation

     2. Diseased fetuses that are too weak to move into the correct orientation (placentitis)

     3. Inappropriate early intervention, where the fetus has not yet had time to turn

In some cases it is easier to simply grasp the presenting limbs and try to rotate the foal, otherwise it may be possible to pull the head into the birth canal and use traction to start delivery while turning the foal 45 degrees. In other case the limbs have to be chained, repelled the head turned and then the limbs started.

Hind end coming first (posterior presentations)

Posterior Presentations: This is a problem in horses because the presentation of the fetal hind limbs does not stimulate the dam to strain very much, normally a head is presented in the vagina, and this is a huge stimulus for the mare to release oxytocin (the Ferguson reflex) and for the mare to push. Many fetuses die in posterior presentation because the owners think the mare is still in the early stage of labour, while she is ready to deliver. The mare's uterine contractions eventually separate the placenta and the foal asphyxiates. The final presentation of the fetus is determined around the 7 - 8th month and fetus cannot readily change the orientation of its long axis, because it is too large to turn near term. The other problem is that during delivery there may be cord compression resulting in birth related hypoxia. These foals may appear normal at birth, but then as their brain starts to swell as an aftermath of the hypoxia they may turn into dummies, have seizures etc. These foals may also be bad right from birth (no righting reflex, no suck reflex, can't thermoregulate, can't stand, depressed...)

Side ways fetus

(Transverse presentation) is the rarest with either all 4 legs coming (transverse ventral) or the back being presented (transverse dorsal). Try to turn under anesthesia or perform a fetotomy

Positional Problems are common

Carpal flexion, Contracted tendons, Poll Lock, Head Back, Dog sitting, Hock flexion, Breech and Twins

There is a large list of complications that may arise as a consequence of dystocia

Rectovaginal Fistula - often maiden mares. A foot gets caught in a dorsal vaginal fold usually above the urethral tubercle, or the foot - nape position; Uterine laceration or rupture; Vaginal laceration, hematoma or rupture; Cervical laceration; Bladder rupture, Bladder prolapsed, Rectovaginal injury; Perineal laceration; Uterine prolapse; Rectal prolapse; Retained placenta; GI complications; Peritonitis; Fatal hemorrhage broad ligament or uterus; Endometrial deterioration; Metritis - laminitis – toxaemia; Maternal intensive care, Neonatal intensive care; Dead foal; Dead Mare