DEALING WITH EQUINE DYSTOCIA IN THE FIELD
Tom A.E. Stout
Utrecht University, Faculty of Veterinary Medicine, Department of Equine Sciences, Utrecht, the
Netherlands
Introduction
Parturition in the mare is a rapid event involving considerable expulsive forces, and
during which the foal must undergo coordinated changes in position and posture in
order to progress from the fetal orientation (lying on its back with forelimbs and neck
flexed) to a disposition compatible with passage through its dam’s pelvis and vagina
(extremities extended and rotating about the long axis so that its sternum passes
along the mare’s ventral pelvis). Given the considerable length of a foal’s extremities
and the complexity of the positional and postural changes required, it is perhaps
remarkable that the majority (approximately 90-95%) of equine births progress
without complications (Frazer et al., 1999a). Nevertheless, failure of one or more of
the extremities to extend properly into the birth canal is the most common cause of
equine dystocia. By contrast, fetal-maternal disproportion (i.e. a foal too large to pass
intact through the pelvis) is rare in horses (<2% of dystocias; Frazer et al., 1999b)
and, in the author’s experience, only regularly encountered in draft and miniature
breeds. Abnormalities of presentation are also uncommon, with posterior
presentation a feature of only 1%, and transverse presentation only 0.01%, of normal
pregnancies (Vandeplassche, 1987), although transverse presentation is
considerably more common in Friesian and draft horses (Maaskant et al., 2010).
Dystocia in the mare must always be treated as an emergency since even a
relatively minor delay in the progression of delivery can be life-threatening for the
foal. Indeed, fetal hypoxia or death due to reduced placental function or placental
detachment is likely if delivery is not completed within 45-60 minutes of the onset of
second stage labour (i.e., rupture of the chorio-allantoic membrane and/or onset of
abdominal contractions; Frazer et al, 1999a). Moreover, because most mares
continue to strain violently as long as fetal parts are present in the vagina, dystocia
and/or attempts to correct the dystocia can endanger the life or the future fertility of
the mare by inflicting severe trauma to the genital tract or other abdominal or pelvic
structures. While speed is therefore of the essence when dealing with equine
dystocia, it is still important to assemble relevant background information via a brief
history and general clinical assessment prior to obstetrical examination, since this
may influence the subsequent therapeutic approach. While the majority of equine
dystocias can be corrected on farm, the exact approach may still depend on the
stage of parturition, the condition and behaviour of the mare at presentation, whether
the foal is alive, the equipment and facilities available, the experience and
competence of the veterinarian and lay assistants, the value (financial or emotional)
of mare and foal, the wishes of the owner, and proximity to a referral centre.
Proceedings
of
the
South
African
Equine
Veterinary
Association
Congress
2016
241