For veterinarians, theyre painted in a brighter light than other equine delivery methods, but in actuality come with enough complications that should be considered. Lets explore, stage by stage.
pictureguy32 / stock.adobe.com
The normal gestational length for a horse is approximately 11 to 12 months. So, for close to a year, owners, trainers, barn managers and veterinarians alike eagerly await the arrival of a healthy foal. Unfortunately, this excitement and anxiety can come to an abrupt halt in a matter of minutes. The actions and decisions of a select few during these minutes can have a profound effect and lasting consequences.
Parturition has long been established to be a series of coordinated events, otherwise known as stages. In its most simplified description, the fetus gets into position during stage one, is born during stage two, and the remaining fetal membranes are removed during stage three.
Problems certainly can arise during any stage, potentially influencing subsequent stages, though delays in stage two generally garner the most attention, with good reason. Stage two delays or problems are the definition of a dystocia and represent the most vital point of intervention for the veterinarian. Recognition of dystocia, the decision making that accompanies it, and the expediency of action greatly influence neonatal survival, future reproductive soundness and, occasionally, mare survival.
The options for delivery of a living fetus during a dystocia include controlled vaginal delivery (CVD), assisted vaginal delivery (AVD) and cesarean section. A fourth option, fetotomy, is a reasonable option for elimination of the fetus from the uterus, but should be reserved only for a nonviable fetus.
AVD, or fetal repositioning when the mare is awake, differs from CVD in which fetal manipulation occurs while the mare is anesthetized, positioned in dorsal recumbency and has her hind end lifted off the ground.
A landmark paper in the Equine Veterinary Journal evaluated cesarean section and other methods of assisted delivery for mare mortality and complications. Data from 116 mares that had cesarean section or vaginal delivery were grouped and analyzed as follows: dystocia corrected by cesarean section, elective cesarean section, cesarean section concurrently with colic surgery, AVD and CVD.1
When excluding the group that had concurrent colic surgery, the survival rate for horses undergoing a cesarean section was 88%, with all mares undergoing an elective cesarean section surviving. The group of horses that had a cesarean section along with colic surgery had the lowest survival rate at 38%. In mares presenting with dystocia, those undergoing a cesarean section or AVD had significantly lower mortality rates (15% and 14%, respectively) than those undergoing CVD (29%).
It is very reasonable to wonder why each path was chosen and the circumstances surrounding the cases, which is always difficult to tease out of a large case series. The authors did note that there were no differences between groups for duration of dystocia.
The knee-jerk reaction to this paper is that cesarean sections (especially elective) are great and CVDs are not … but why wouldn't everyone just proceed to a cesarean section if AVD is unsuccessful?
The answer to this question is clearly complicated. For many horse owners, financial limitations may make CVD the only option, even when positioning of the fetus, time, trauma to the mare and clinician experience could suggest it's not the wisest option.
Along those lines, experience with mares with dystocia cannot, and should not, be overlooked. Clinicians and veterinary teams that do not routinely attend these cases will not have as good of a feel for timing of correction, techniques for efficient correction and the effects of applied force leading to tissue trauma. Spending a lot of time trying to correct a difficult malposition, or applying great force to do so, may lead to increased soft tissue damage that then leads to complications such as hemorrhage, metritis, uterine tear, peritonitis, sepsis, laminitis, future reproductive unsoundness and, ultimately, death.
CVDs are the in-between “gambling zone.” What I mean by this is for most, if not all, AVDs, the positioning and correction are simple and quick, leading to a positive outcome for mare and, oftentimes, foal. For difficult or impossible malpositions, the attending clinician will likely decide to proceed to cesarean section without attempting CVD-a decision that also improves mare and, potentially, foal survival.
It's the in-between cases and fetal positions that generally undergo a CVD, and have the biggest variability in decision making, human error and outcome. In the hands of experienced and knowledgeable clinicians, CVD is a fantastic method of delivering a foal from a mare with dystocia that can result in a live foal and mare while preserving reproductive soundness. However, it's essential that the technique is expertly executed to maximize the benefits.
As Rolf Embertson said, “The only definitive procedure that can be used with relative safety to remove any foal from any mare in dystocia is the cesarean section.”2 This point is without question, but, as he went on to point out, many circumstances do not call for such efforts.
Furthermore, cesarean sections are not without complications: hypotension and hypoperfusion during anesthesia, uterine hemorrhage, abdominal contamination, peritonitis, retained placenta, laminitis, incisional infection, hernia formation, body wall or incision failure, and evisceration. For many of these complications, surgical technique influences their potential.
Once anesthetized, positioned into dorsal recumbency, clipped, sterilely prepared and draped, a caudal ventral midline incision is made and the uterine horn containing the hindlimbs is identified and exteriorized, if possible. The abdomen is packed around the uterine horn and an impervious drape is placed around the horn in an effort to minimize contamination from hair, uterine fluids containing lube, hippomane and potentially meconium into the abdomen following incision into the uterus.
Additionally, stay sutures and an assistant are vital to managing abdominal contamination. Once prepared, a process that should occur with expediency, an incision is made into the uterine horn, using the point of the hock of the fetus as a guide. Take care to not incise the foal and make sure the incision is large enough to deliver the foal. Having a team ready to help remove the foal and resuscitate if necessary is recommended. Once removed from the uterus, the foal's umbilicus is clamped and transected before the animal is passed to the neonatal care team.
Following delivery, the primary goal of the surgical team is closure of the uterus with minimal spillage, hemorrhage and retention of fetal membranes. This is achieved by holding the incision up with the stay sutures or lap sponges, ligating any large vessels and separating the chorioallantois from the endometrium along the incision, respectively.
Some surgeons recommend placing a hemostatic suture along the margins of the incision prior to closing the uterus. Introduced in 1980, this recommendation was made in response to a 6% mortality rate from uterine hemorrhage in mares undergoing cesarean section.3 This recommendation was reevaluated 20 years later, concluding that the hemostatic suture did not significantly reduce the incidence of severe uterine hemorrhage or postoperative anemia.4 Therefore, the decision to perform a hemostatic suture should remain a decision of preference by the attending surgeon.
The uterus is then closed in typically two layers with the outer layer inverted to minimize adhesion formation through suture exposure. The suture type and pattern are surgeon dependent. Once the uterus is closed, oxytocin should be administered intravenously to contract the uterus and help to expedite stage three of labor. The uterus is returned to the abdomen, the abdominal packing and impervious draping removed, and the abdomen is lavaged with a large volume of sterile isotonic fluids. The decision to place an abdominal drain for postoperative lavage should be based on the effectiveness of intraoperative lavage and degree of contamination. The ventral midline incision is then closed in two to three layers, per the surgeon's preference.
The primary postoperative targets for intervention and monitoring are passage of the placenta, infection and hemorrhage, with the most detrimental sequelae being sepsis, endometritis, hypoperfusion and sepsis. If the placenta is passed in a timely manner, the uterus is typically lavaged for a few days and with contraction aided by administration of oxytocin.
The ideal scenario following a cesarean section is survival of the mare with minimal morbidity, maintenance of reproductive soundness and delivery of a live, healthy foal. The latter is unfortunately oftentimes the limiting factor to an ideal scenario. In the aforementioned groups of delivery, the overall survival rate of foals delivered following dystocia was 11% at the time of delivery, which dropped to 5% by discharge.1
There was no difference in foal survival based on technique used to deliver the foal from mares with dystocia. The survival rate in this study1 was much lower than the 30% reported 6 years earlier5 and the 35% in 2012.6 In that study, only foals delivered by cesarean section were reported. Also worth noting from the 2012 study was an overall mare survival rate of 84% following cesarean section, with mares having dystocia for around 90 minutes having the fewest complications.
Finally, data on reproductive soundness following cesarean section are important to know when discussing outcome and prognosis with owners. Of the 95 mares undergoing cesarean section in the report, there was a cumulative foaling rate of 77% prior to the procedure.6
Following cesarean section, the cumulative foaling rate for those mares 3 years after the procedure dropped to 52% or 68% depending on if the duration of dystocia was greater or less than 90 minutes, respectively. This report gives credence to the mantra that time matters and that, while effective, cesarean sections are not benign.
As experience and literature have shown, mares with dystocia, as well as the cesarean sections that oftentimes accompany them, can be troublesome to both mare and foal. However, through sound judgment and decision making, good surgical technique and attentiveness to potential complications, mare survival and reproductive soundness can have a good prognosis, while foal survival remains an area of emphasis for improvement across the profession.
Dr. Jarred Williams is a clinical associate professor in Large Animal Emergency Medicine and Surgery at the University of Georgia College of Veterinary Medicine.
1. Freeman DE, Hungerford LL, Schaeffer D, et al. Caesarean section and other methods for assisted delivery: comparison of effects on mare mortality and complications. Equine Veterinary Journal 1999;31(3):203-207.
2. Embertson RM. Dystocia and caesarean sections: the importance of duration and good judgement. Equine Veterinary Journal 1999;31(3):179-180.
3. Vandenplassche M. Obstetrician's view of the physiology of equine parturition and dystocia. Equine Veterinary Journal 1980;12:45-49.
4. Freemand DE, Johnston JK, Baker GJ, et al. An evaluation of the haemostatic suture in hysterotomy closure in the mare. Equine Veterinary Journal 1999;31(3):208-211.
5. Vandenplassche M. Dystocia. In McHinnon AO, Voss JL, Eds: Equine Reproduction. Philadelphia: Lea and Febiger; 1993:578-587.
6. Abernathy-Young KK, LeBlanc MM, Embertson RM, et al. Survival rates of mares and foals and postoperative complications and fertility of mares after cesarean section: 95 cases (1986-2000). Journal of the American Veterinary Medical Association 2012;241(7):927-934.