IN-DEPTH: CONDITIONS AND MANAGEMENT OF THE PERIPARTUM MARE


8. Maternal Disease Conditions and Musculoskeletal Problems Affecting Pregnancy


Maternal disease conditions, particularly colic in late pregnancy, can be challenging to manage. First of all, colic pain has to be distinguished from the abdominal discomfort associated with parturi- tion. Ideally, the overall strategy adopted will be to save the life of the mare and at the same time maximize the likelihood of the foal surviving as well. In most situations this will require the fetus to re- main in utero because of the risks associated with the foal not being ready for birth. Economic con- siderations and the stage of gestation may in some circumstances significantly alter this approach. The conditions most of concern in the late pregnant mare are those related to endotoxemia and include colitis, large colon displacements and torsions, ante- rior enteritis, and a variety of other small intestinal conditions. Profound disturbances in systemic cir- culation may be also involved in these conditions which may critically affect uterine perfusion and placental transfer of oxygen and nutrients to the fetus. Recurrent pain unrelated to the gastrointes- tinal tract may have a reproductive tract origin and conditions include uterine hemorrhage and uterine torsion. The latter is relatively uncommon and the pain level is generally not as severe as that associ- ated with intestinal displacements, especially colon torsions, which can be violently painful. Diagnosis of abdominal conditions can be a chal-


lenge in the late pregnant mare due to the size of the pregnancy and the amount of space in the caudal abdomen it occupies. Rectal palpation may allow only limited assessment of the gastrointestinal tract, and ultrasound both transrectal and transab- dominal, may be more useful to identify free fluid in the peritoneal cavity or distended small bowel or the thickened and edematous colon wall present in colon displacements. Similarly, abdominocentesis may be difficult, unless undertaken with ultrasound guidance, as the gravid uterus will generally occupy the full ventral extent of the abdomen in late preg- nancy. Increased cell counts and protein levels may reflect disease associated with either compro- mised uterine or bowel wall. Although, many causes of abdominal pain are not serious and may reflect changes in dietary management of the mare some conditions will require surgical correction. Occasionally, standing surgery may be appropriate, for example many cases of uterine torsion are more easily corrected by a standing flank laparotomy; however, it is more likely an exploratory laparotomy in dorsal recumbency will be required. Maintain- ing oxygenation of the mare is challenging in these circumstances with the weight of the gravid uterus pressing down on the diaphragm and even ventila- tion may not prevent low oxygen tensions and an inevitable degree of severe fetal hypoxia. Particu- larly in late pregnancy the oxygen demands of the rapidly growing fetus are high.29 Similarly main-


taining maternal blood pressure and therefore avoiding reduced uterine and fetoplacental perfu- sion must also be addressed. Generally, the mare’s survival is more important and supersedes the foal in these circumstances; however, normally the foal’s best chance will be if it can remain in utero until it has fully matured and be delivered normally at full term. Although postoperative dehiscence of the midline incision is generally a concern in late preg- nant mares following surgery, especially if a large incision is necessary, wound dehiscence and the risk of catastrophic bowel evisceration at the time the mare foals or that she will have difficulty producing sufficiently strong abdominal contractions is rare. Ultrasound monitoring of the midline wound can detect any suspicion of wound breakdown and the common use of colic belly bandages has improved the management of these type of wounds. As men- tioned earlier, the use of a large-dose dexametha- sone regime to promote fetal maturation may again be appropriate in pregnant mares, post colic surgery, in some instances. While the mare is hos- pitalized, continuous telemetric fetal electrocardio- graphic monitoring may be practical and allow close assessment of fetal wellbeing and detect any early indications of fetal compromise. This may be par- ticularly important if the mare has postoperative complications from endotoxemia, anemia, and hy- poalbuminemia. Telemetric systems, (e.g., Kruuse Televet 100)f allow continuous recordings to be eas- ily made. Both heart rate and heart rate variabil- ity can be determined. Decreasing heart rate and increasing heart rate variability parameters indi- cate maturation of the fetal autonomous nervous system. Accelerations and decelerations in heart rate are easily detectable. Accelerations often oc- cur with fetal movements and indicate wellbeing in the fetus. A recent study of heart rate variability in normal mares and their fetal foals in late gestation only showed significant changes in fetal heart rate variability in the last few minutes before foal- ing.30,31 For the 10 days prior to foaling, fetal heart rate (FHR) and heart rate variability remained con- stant and did not predict the beginning of foaling. Only during the last 30 minutes before delivery, in the majority of fetuses, did FHR decrease and RR interval increase. Accelerations and decelerations in FHR were detectable at all times, but neither their number nor duration changed over time. In human fetuses, reduced heart rate and decelera- tions in heart rate are considered signs of fetal com- promise. Therefore, unstable heart rate variability parameters in the days before foaling, a reduction in the number of accelerations, and an increased num- ber of decelerations may indicate a pregnancy at risk. Continuous telemetric fetal heart rate moni- toring is a potentially useful technique especially where continuous assessment of fetal health is needed in response to a rapidly changing clinical situation.


AAEP PROCEEDINGS  Vol. 65  2019 155


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