18 Aug 2026
Victoria Colgate MA, VetMB, MSc, MRCVS previews her session, during which results from a UK hospital study will be presented for the first time.
Victoria Colgate
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Image: Lynsview / Adobe Stock
In general, parturition in the mare proceeds uneventfully and dystocia is a rare event, with a reported prevalence of only 2% to 13% (Merari and Fielding, 2025).
However, when dystocia does occur, it comprises a true emergency where every minute can make a difference, not just to mare and foal survival, but also to maintenance of breeding soundness and to future athletic potential, respectively.
Early detection by owners, followed by rapid procurement of veterinary assistance and determination of the cause of the dystocia, are vital first steps. Quick and informed decision-making must follow, which requires the clinician to have a thorough understanding of the normal physiology of parturition and the resolution options available. But it cannot be emphasised enough that unless correction looks to be simple, early and expedient referral to a hospital setting, if possible, is of paramount importance.
As is inherently desirable for a prey species, normal parturition in the mare is a rapid process that has often been described as “explosive” (Maaskant et al, 2010). Stage II labour, from rupture of the chorioallantoic membrane to delivery of the foal, should take between 20 to 30 minutes and it has been shown that for every 10-minute increase in duration across 30 minutes, risk of stillbirth increases by 10% (Norton et al, 2007).
This limited time window of viability is the result of early placental separation during the delivery process, meaning any delays risk fetal hypoxia with potential progression to asphyxia. Accordingly, a successful outcome, in particular for the foal, is extremely time sensitive.
Dystocia refers to any deviation from the normal parturition process and can have fetal, maternal or fetal membrane causes. Red bag delivery (premature separation of the chorioallantois) is really the only common fetal membrane cause and, in this instance, guided action by the owner/foaling attendant is vital as dystocia resolution cannot wait for clinician arrival.
Maternal causes encompass primary and secondary uterine inertia, plus anomalies of pelvic anatomy or incomplete dilation of the birth canal leading to relative fetopelvic disproportion, but overwhelmingly dystocia in the mare is of fetal origin.
Absolute fetopelvic disproportion describes the situation where the fetus is simply too large to pass through the birth canal. Although this does occur in the mare, it is comparatively rare to incidences recorded in bovine species, as mare uterine size limits growth to dictate foal size, making oversize uncommon even after prolonged gestation (Gormley, 2021). Thus, as has been overwhelmingly demonstrated by the published literature, dystocia in the mare is most commonly caused by abnormalities of fetal presentation, posture and/or positioning.
In normal parturition the foal would have: an anterior presentation with head and forelimbs entering the birth canal first; a dorsosacral position with the dorsum of the foal against the mare’s sacrum; and an extended posture with both forelimbs, the head and the neck extended.
Any deviation from this may lead to dystocia – usually a normal anterior presentation, but with single or multiple postural abnormalities being particularly common and often caused by rigid flexural deformities and other congenital conformational abnormalities.
Although the published literature on dystocia management and associated prognosis is limited, the consistent message is of early referral and minimised dystocia duration leading to the best outcome for the foal, plus benefits for the mare. Additionally, no single resolution method is the most appropriate for every dystocia presentation and owner situation, meaning critical assessment of progress with the selected method, and a willingness to change the plan, is essential.
Meaningful progress has been defined as correction of a maldisposition every five minutes (Woodford, 2025) with conversion to caesarean section (C-section) if delivery is not achieved within 15 minutes of attempts at controlled vaginal delivery (CVD; Abernathy-Young et al, 2012).
Overall, four methods are available for dystocia resolution, but before any interventions are initiated, a cursory physical examination of the mare should be carried out and relevant obstetric history, such as the due date and duration of the current dystocia, obtained.
It is particularly important to ascertain any potential for infectious disease, and differentiate abortion over an at-term dystocic delivery. Additionally, determining whether the mare, or foal, are the bill payer’s priority is a useful early step. Theoretically, it is important to determine fetal viability as this has bearing on selection of the most appropriate correction method. However, this can sometimes be difficult to definitely elucidate as fetal hypoxia can cause absence of reflexes and a slowed pulse (Lu and Sprayberry, 2021).
Assisted vaginal delivery (AVD) refers to manual manipulation of the foal in the birth canal with the mare conscious, but sedated. In reality, in referral centres this is usually rarely performed due to previous attempts at such an assisted delivery by stud personnel or the ambulatory clinician.
On hospital arrival of the mare, it would be more normal to proceed straight to CVD, which involves anaesthetising the mare and placing her in the Trendelenburg position with the hindquarters hoisted off the ground. This positioning allows gravity to assist with repulsion of the fetus and the general anaesthesia causes cessation of all abdominal and myometrial contractions to ease manipulation of the fetus within the confines of the mare’s pelvis.
It is commonplace to start preparing the abdomen for a C-section during attempts at CVD – so that conversion to the former procedure can be rapidly achieved if required. It should be borne in mind that even in the face of an already dead fetus, attempts at CVD should not be excessively prolonged as repeated manipulations risk abrasive trauma to the mare’s reproductive tract with potential consequences of adhesions endangering her future reproductive career (Gormley, 2021).
C-section in the emergency dystocia setting is usually performed following failed attempts at CVD, but it can also be carried out due to maternal disease such as uterine torsion or colic, which is compromising the foal, or as an elective procedure when a difficult delivery is expected, that is, in a mare with a history of a pelvic fracture.
Fetotomy refers to reduction in the size of a dead fetus by a number of cuts, to enable easier passage through the birth canal and avoids the costs and risks associated with a C-section when you are confident the fetus is deceased. Although rarely used and often regarded as presenting significant risk of reproductive trauma for the mare, when a partial (1-3 cut) fetotomy is performed by an experienced clinician in a good candidate with minimal swelling of the reproductive tract, it can be a safe technique that does not impair short-term fertility (Abernathy-Young et al, 2012).
Overall, the best method of correction must be the one most likely to deliver the foal in the shortest timeframe, while minimising trauma to the mare.
Independent of the cause of dystocia and method of resolution, mare survival following dystocia is universally reported as high, justifying referral and treatment even if the foal window of viability has passed (Norton et al, 2007). However, in the short term, dystocia and its resolution is a risk factor for the development of: retained fetal membranes, laminitis, metritis, delayed uterine involution, peritonitis, uterine prolapse, haemorrhage, neuropraxia and neuroparesis, leading to a survival drop off when you consider those making it to hospital discharge.
Another pertinent consideration is the longer-term impact on breeding soundness. Mares suffering from a previous dystocia episode have been shown to be significantly more likely to suffer from dystocia on a subsequent occasion (Ellerbrock et al, 2024) and reductions in future fertility are recorded, significantly so if mares were rebred in the same year in which a C-section was performed (Abernathy-Young et al, 2012). But the counter is that mares certainly do recover and have shown sustained future fertility, with production of many further live foals in the future.
Foal survival following a dystocic delivery is variable, but overwhelmingly low, with rates reported between 4% to 31% (Maaskant et al, 2010). Overall, method of resolution does not seem to significantly impact fetal survival, with Bryon et al (2003) reporting survival rates of 32% and 31% for foals following CVD and C-section respectively. Time, however, has clearly been shown to have a substantial impact with prolongation of stage II labour beyond 40 minutes being associated with a significant increase in fetal mortality (McCue and Ferris, 2012).
Even following delivery of a live foal, there is notable short-term mortality risk during hospitalisation associated with potential hypoxic injuries sustained during delivery, plus owner elected euthanasia of foals suffering from congenital malformations – often the cause of the dystocia in the first place.
Although, in the equine population overall, dystocia is a rare event, it forms a significant caseload for some referral centres and yet the published data is sparse and comparisons are limited by inconsistent definitions and lack of generalisability.
With prognostic indicators being fundamental to owner-informed decision-making and up-to-date data essential to optimising veterinary management, further research is needed.
On the Thursday of this year’s BEVA Congress, in the first clinical research session, we aim to start the conversation and present results from dystocia management in a UK-based hospital for the first time.
Victoria Colgate qualified from the University of Cambridge in 2014, and then completed a clinical training scholarship at its equine hospital before working in a busy polo practice in Ascot. She joined Rossdales Equine Hospital in June 2017 as the Margaret Giffen resident in clinical research, where, in addition to carrying out research projects, she attained an MSc in Veterinary Epidemiology and Public Health. After time away in a specialist role as a veterinary epidemiologist at Equine Infectious Disease Surveillance (EIDS), Vicky returned to Rossdales in July 2023 as a research associate, a role funded by the Margaret Giffen Charitable Trust.