Dystocia in Horses

Dystocia
Risks
Causes
Terminology
Clinical Signs
Diagnosis
Treatment
Summary

Dystocia, or difficulty giving birth, is a relatively rare complication in horses occurring in less than 10% of foalings. ^[1] Dystocia carries significant risks for both the mare and foal, including damage to internal organs, nerves, and blood supply for the mare, and reduced oxygen availability for the foal.

The main sign of dystocia is a delay of 20 – 30 minutes between the release of chorioallantoic fluid from the mare’s vulva and delivery of the foal. Other signs include failure to see any portion of the foal at the vulvar lips, or abnormal positioning of the foal.

If your broodmare is showing signs of dystocia, contact your veterinarian immediately. Prompt intervention is critical for the well-being of both the mare and the foal.

Diagnosing dystocia requires inspecting the vaginal canal to determine the foal’s position and assess if surgical intervention is needed for its removal.

Most cases of dystocia are treatable on farm by repositioning the foal within the uterus to allow a smooth delivery. In severe cases or when manual repositioning fails, referral to a surgical hospital allows for Caesarean section or controlled delivery under anesthesia.

With appropriate intervention, dystocia can result in the delivery of a healthy foal. Supervision of mares when they are close to delivery is the best method of identifying dystocia early enough to allow successful intervention.

Dystocia, a term derived from Greek words meaning ‘difficult birth,’ is a medical condition observed in many animals, including horses. In equines, dystocia refers to complications that arise during the delivery of a foal and occurs in approximately 4% of foalings. ^[1]

Dystocia encompasses a range of complications such as prolonged labor, evident distress in the mare, or delivery that appears to have stalled. Some breeds, such as draft horses, Friesians, and Shetlands, and Miniature horses, may have a higher risk of dystocia. ^[2]^[3]

In horses, dystocia is most commonly caused by abnormal positioning or posture of the foal within the mare’s reproductive tract. ^[1]^[4] Mares experiencing dystocia require rapid intervention to correct the foal’s position and allow for a smooth delivery.

Risks

Dystocia is risky for both mares and foals. Once labour begins, uterine contractions continue even if the foal is stuck in the birth canal.

Risks to the Mare

For the mare, this can result in several serious, potentially life-threatening conditions such as:

Tearing of the reproductive tract from the foal’s movement

Traumatic injury to the intestinal tract or other organs by the foal

Retained placenta, resulting in sepsis and laminitis

Laceration of the uterine arteries by the foal

Paralysis of the hindquarters from nerve damage ^[4]^[5]

Mares that survive dystocia often have reduced fertility in future breeding cycles due to damage in their reproductive tract, particularly if the dystocia is prolonged. ^[4]^[5]

Risks to the Foal

In foals, dystocia compromises the delivery of oxygen, which can potentially lead to hypoxia, brain damage, or even neonatal death if not promptly addressed.

Once labour begins, the ability of the placenta to provide oxygen to the foal is reduced, necessitating a rapid delivery to allow the foal to take its first breath.

In cases of dystocia, the foal cannot yet breathe on its own, but does not receive adequate oxygen from the placenta. These foals have a very high risk of neonatal asphyxia or “dummy foal syndrome”. ^[4]^[5]

One study found that for every ten-minute increase in duration of this stage of labour, there was a 10% higher risk of the foal being stillborn. ^[1]

Causes

Dystocia can arise from various causes, each contributing to complications that affect the foal’s movement through the birth canal during the birthing process.

Abnormal Foal Positioning

The most common cause of dystocia is abnormal positioning of the foal within the birth canal, preventing smooth delivery. Any alteration in the position of the foal can potentially result in dystocia, as the mare’s pelvic canal is very narrow relative to the size of the foal. ^[4]

Fetal Oversize

Unlike other species, fetal oversize is rarely the cause of dystocia in horses. Mares appear to regulate fetal growth according to the capacity of their uterus, thereby minimizing the chance of producing a foal too large for safe delivery. ^[4]

Fetal oversize is more common in young, maiden mares who may not be fully grown at the time of delivery. ^[4]

Malformations

Malformations of the foal contribute significantly to dystocia, with contracted limbs being the most common cause. Foals with contracted limbs cannot fully extend their legs, preventing them from positioning themselves correctly within the uterus prior to delivery. ^[4]

Other malformations that can cause dystocia include facial malformations such as wry nose, or abnormalities in the spine such as scoliosis.

Hydrocephalus

In pony breeds, hydrocephalus is an important cause of dystocia. This condition arises when the cerebrospinal fluid around the brain fails to drain properly and begins to accumulate, resulting in a head that is two to three times normal size. ^[4]

Uterine Torsion

Rarely, dystocia results from uterine torsion, where the uterus twists around the foal and closes off the opening to the birth canal. ^[6]^[7]

Terminology

Veterinarians use specific terminology to describe a dystocia event and indicate the position of the foal within the mare prior to delivery. The main components of a dystocia description are the presentation, position, and posture of the foal.

Presentation:

Presentation refers to the direction the foal is facing within the mare, or which aspect of the foal is closest to the vulva.

During a normal delivery, foals have a cranial position, indicating that the foal is coming out of the vulva head-first. Foals coming out tail-first have a caudal presentation.

In rare cases, ventro-transverse presentations occur, where the foal is rotated within the uterus such that their legs are pointing towards the vulva.

Similarly, dorso-transverse presentations occur when the foal is rotated with their back pointing towards the vulva. ^[4]

Position:

Position describes how the foal is sitting relative to the mare’s pelvis. Most descriptions use the position of the foal’s back as a landmark, then identify what portion of the mare’s pelvis the foal’s back is next to.

For example, normal delivery has a dorsosacral position, meaning that the foal’s back (dorsum) is next to the mare’s sacrum (the top portion of the pelvis).

Foals that are “upside down” have a dorsopubic position, meaning that their back is against the mare’s pubic bone (the bottom of the pelvis).

Foals can also be found in right or left dorsoilial, meaning that their back is against either the right or left ilium (sides of the pelvis). ^[4]

Posture:

Posture indicates the positions of the foal’s head, neck, and limbs relative to its body. A normal delivery will have the foal extending its front limbs, head, and neck forward in a “diving position” to enter the pelvic canal.

Dystocia can occur if any portion of the foal is not in a correct position, as the foal will be unable to slide smoothly through the narrow passageway of the pelvis. ^[4]

Clinical Signs

Symptoms of dystocia develop once labour begins, and timely recognition is crucial to ensure the safety of both the mare and the foal.

If your broodmare is close to her due date, stay vigilant for signs that delivery is beginning so you can intervene if there are complications.

Signs that a mare is close to foaling include the following:

Softening of the tail head and relaxation of the vulva

Increase in the size of the udder

Wax-like material accumulating on the teat tips

Milk streaming from the udder ^[4]^[8]

Progression of Labour

During a normal birth, mares go through three stages of labour.

Stage One: In the first stage of labour, uterine contractions begin, causing restlessness or mild colic signs. Mares may lay down and get up frequently during this time, which is thought to assist in positioning the foal for delivery. ^[4]

Stage Two: As birth progresses, the chorioallantois portion of the placenta will rupture, releasing large amounts of watery fluid from the vulva, indicating the start of the second stage of labour. ^[4] During stage two, strong uterine contractions push the foal out of the uterus within 20-30 minutes. ^[4] The normal birth position for foals is a dorsosacral and cranial position.

Stage Three: Finally, stage three of labour involves passing of the placenta from the uterus.

Symptoms of Dystocia

A diagnosis of dystocia is made if the foal is not delivered within 20 – 30 minutes of the chorioallantois rupturing. ^[4]

Other possible signs of dystocia include:

Failure to see a hoof at the vulvar lips within five minutes of the chorioallantois rupturing

Seeing hooves that are facing upwards, rather than pointing downwards in a normal delivery position

Identifying anything other than two front feet and a head in “diving position” during vaginal examination of the mare

Little evidence of uterine contractions in the mare ^[4]^[9]

Diagnosis

Dystocia must be diagnosed quickly, as the risks to both the mare and foal are high. The simplest method of diagnosis is a vaginal examination, where a veterinarian palpates within the mare’s vaginal canal to identify which foal structures are present.

Based on their palpation, they can often determine the position, presentation, and posture of the foal to diagnose the type of dystocia present. Most dystocias have a normal delivery position and presentation, with only the posture of the foal’s head, neck, or limbs impeding delivery.

Types of Dystocia

The most common types of dystocia in horses are:

“Head back” posture: Foal’s head and neck turn to the side or downwards, preventing the foal from entering the birth canal

Carpal flexion: One (or both) of the foal’s knees are flexed

Shoulder flexion: One or both front limbs point downwards and remain in the uterus, while the head and neck enter the birth canal

Foot-nape posture: Positioning of the forelimbs above the head

“Dog-sitting” posture: The head and all four limbs are present within the birth canal ^[3]^[4]^[6]^[7]^[9]

Your veterinarian will also check to see if the foal is alive and whether there are any serious, life-threatening conditions impacting the mare’s overall health such as hemorrhage or tearing in the reproductive tract. These factors determine whether the dystocia is treatable on farm, or if referral to a surgical facility is required.

Treatment

The appropriate course of treatment depends on the type of dystocia, whether the foal is alive, and other considerations including the mare’s overall health.

The main options for dystocia treatment are:

Assisted vaginal delivery – in which a veterinarian attempts to correct the foal’s position in a conscious mare

Controlled vaginal delivery – in which the mare is anesthetized to allow the veterinarian full control over the delivery process

Caesarean section – in which the foal is surgically removed from the mare’s uterus

Fetotomy – in which a stillborn foal is cut into sections for easier removal from the uterus ^[3]^[4]

Treatable on Farm

Many cases of dystocia are treatable on farm through assisted vaginal delivery. Assisted vaginal delivery often requires the veterinarian to push the foal back into the uterus, to give themselves more room to change the foal’s position.

After this adjustment, strategies used to correct the foal’s position include:

Manually adjusting the foal’s limb position through careful movements, ensuring that the foal’s hooves do not damage the uterine wall

Using a head snare to wrap around the foal’s head to pull it into position

Wrapping chains or ropes around the foal’s limbs to hold them in a particular position ^[3]^[4]

It is important to never attempt to correct a dystocia without a veterinarian present. During dystocia, the mare’s reproductive tract is extremely fragile, and can easily tear.

If assisted vaginal delivery does not result in delivery of the foal within 15 – 20 minutes, the mare should be referred to a surgical hospital to provide the best prognosis for both mare and foal.^[3] In cases where the foal has died, fetotomy can be done on-farm by experienced practitioners.

Not Treatable On Farm

The following types of dystocia are not treatable on farm and require an immediate referral to a veterinary hospital:

“Breech” presentation: The foal is presenting tail-first with both hindlimbs flexed forwards at the hip

Transverse presentation: The foal rotates within the uterus such that the abdomen or back are pointing towards the vulva

Fetal disproportion: The foal is physically too large to fit through the birth canal opening

Fetal malformations: The structure of the foal physically prevents delivery through the birth canal ^[3]^[4]

These types of dystocia usually require Caesarean section to deliver the foal, regardless of whether the foal is still alive. ^[3] Survival rates for mares following Caesarean section are relatively high at between 81-91%, whereas foal survival is much lower at between 4 – 31%. ^[5]

Summary

Treatment of dystocia requires prompt intervention to have the best chance at a favourable outcome for both the mare and foal.

Mares showing signs of nearing delivery should be closely monitored for signs of dystocia. It is important to identify when delivery begins and ensure that stage two of delivery occurs promptly within 20 – 30 minutes of the chorioallantois rupturing.

A veterinarian should be consulted in cases of dystocia to assist the mare during foaling. In some cases, the mare may have to be referred to a veterinary hospital for more intense intervention to increase the survival rate of both mare and foal.