Treatment of Hydropsical Conditions Using Transcervical Gradual Fetal Fluid Drainage in Mares With or Without Concurrent Abdominal Wall Disease

Highlights

• Hydropsical conditions are a medical emergency in mares.

• Hydrallanotis can lead to abdominal wall disease, such as prepubic tendon rupture.

• Leptospirosis is associated with hydropsical conditions.

• Mares with abdominal wall disease may become embryo transfer donors.

• Slow transcervical drainage of fetal fluid is effective for treating hydrallantois.

Abstract

Hydropsical conditions are exceedingly rare in the horse. However, when they occur, they are true emergencies due to the severe enlargement of the pregnant uterus, which can result in clinical signs, such as an enlarged round abdomen, dyspnea, reluctance to walk, and colic, and may lead to the development of abdominal wall disease. The pathogenesis of hydropsical conditions is not fully elucidated, but they have been associated with placentitis and fetal abnormalities. This report describes six cases of hydropsical conditions in mares with or without concurrent abdominal wall disease. Five out of six cases were hydrallantois, and of these five, two mares had abdominal wall disease; the remaining one out of six cases was hydramnios. All mares were treated by termination of the pregnancy through gradual fluid drainage transcervically over a number of hours, and their fetuses were delivered vaginally. All fetuses were euthanized immediately after vaginal delivery. Of the six mares, two had signs of placentitis, two were confirmed seropositive for leptospirosis, and two were euthanized (one because of a vaginal tear that communicated through the peritoneum and one mare that developed abdominal wall rupture and laminitis). The remaining 4 mares were available for follow-up; three mares were not rebred, and one mare became an embryo donor, with a successful embryo recovery. We reported the prevalence of leptospira involvement in two out of six cases of hydrallantois and also described the clinical outcome of the mares after treatment with slow fetal fluid drainage.

Introduction

Hydropsical conditions (hydrops) in horses are very rare but are life-threatening medical emergencies [1]. Hydramnios, the excessive accumulation of amniotic fluid, has been associated with a higher prevalence of fetal abnormalities in cattle and accounts for about 10% of the cases of hydrops in large animals. Hydrallantois is the excessive accumulation of fluid in the allantoic space and accounts for the other 90% of the hydropsical cases [2]. The pathogenesis of hydrallantois is not fully elucidated, and it has been speculated that functional or structural changes in the chorioallantoic portion of the placenta contribute to the abnormal accumulation of fluid in the allantoic cavity [3]. Placentitis and fetal abnormalities have been reported in cases of hydropsical conditions [4], [5], but these problems are not always present [4], [5], [6]. A genetic predisposition to hydropsical conditions has not been established; however, draft horses are more commonly reported as affected [5]. Both multiparous and nulliparous mares have been reported to be affected by hydropsical conditions [1], [4].

Normal fetal fluid volume near term in the mare in the amniotic space is reported to range from about 3 to 5 L, whereas in the allantoic space, there is gradual increase to about 8–15 L at term [7]. Hydropsical cases have a variable range of fetal fluid accumulation, with allantoic fluid being reported from 120 to 220 L [5] and in one mare with hydramnios, with a uterine rupture, an estimated 96 L was present [8]. Hydramnios cases are reported to have a slower progression of fluid buildup, and therefore slower abdominal enlargement, whereas a severe rapid abdominal enlargement within the last 2 weeks before presentation of clinical signs is commonly noted in mares with hydrallantois [2]. Clinical signs also vary and are related to the severity of fluid accumulation and can include severe ventral wall edema, anorexia, dyspnea, reluctance to walk, colic signs such as sweating and shivering, and tachycardia [1]. Complications related to the excessive fluid accumulation and heavy gravid uterus can lead to abdominal wall disease, such as ventrolateral body wall tears and partial or full prepubic tendon (PPT) rupture. Other complications that could arise from hydrops include uterine rupture, abortion, dystocia, and retained placenta [1], [9]. Inflamed painful ventrolateral body wall regions, pitting ventral edema, displacement of the udder cranially, and bloody mammary secretion can be expected if PPT rupture has occurred [10]. Differential diagnoses include twin pregnancy and other causes of colic and ventral edema [1], [9]. A complete physical examination is warranted. Mares may be off feed; reluctant to move; and may have tachypnea, dyspnea, and an elevated heart rate; and/or display signs of shock or colic [1].

Reproductive evaluation of the mare is needed to confirm diagnosis of a hydropsical condition, including transrectal palpation and transrectal and transabdominal ultrasound examination of the pregnant uterus, placenta, fetus, and body wall [2]. Transrectal palpation reveals a very distended uterus that may or may not extend beyond the pelvic brim and a fetus that is not usually palpable [1], [2], [3], [5], [11]. A transrectal ultrasound is performed to evaluate fetal fluid character and depth, to evaluate the area adjacent to the cervix for evidence of placental separation or discharge, and to measure the combined uteroplacental thickness to rule out ascending placentitis [6], [12], [13]. The transabdominal ultrasound is normally used to perform a fetal and placental assessment and also to measure the fetal fluid depth and echogenicity [13]. This approach is used to rule out twin pregnancy [6], [9], [12]. The transabdominal ultrasound can also aid in an evaluation of the body wall to determine if complete prepubic tendon rupture or an abdominal wall defect, such as a ventrolateral hernia, has occurred [10], [14], [15]. Creatinine kinase (CK), alkaline phosphatase, and serum amyloid A (SAA) are usually increased in cases where the abdominal wall is compromised [14], [15].

Treatment is normally focused on salvaging the mare but not the foal, as most cases of hydrops become clinically apparent from 6 to 7 months of gestation to term [1], at a time when the fetus is not viable. However, a single case of hydramnios that presented at 265 days and was medically managed to term has been described, in which the mare delivered a live foal at 321 days [6]. Immediate termination of the pregnancy is generally indicated in confirmed hydrops cases, to avoid complications such as cardiovascular compromise or abdominal wall rupture [1], [9]. Pregnancy may be terminated by induction of parturition and assisted delivery [1] or through transcervical gradual drainage of the fluid through the cervix [4], [9]. The transcervical method is suggested to minimize the risk of splanchnic pooling of blood during or after the termination of pregnancy, which has been suggested to be the cause of hypovolemic shock [5], [8].

Outcome of the mare is dependent on the stage of pregnancy, severity of abdominal enlargement, clinical signs, and the concurrent involvement of abdominal wall disease. Hydropsical conditions have been reported to reoccur [16] in subsequent pregnancies; however, this is uncommon, and mares that have been affected by hydrops have been successfully rebred and carried subsequent healthy pregnancies [3], [5]. In this report, six clinical cases of hydropsical conditions, treated via transcervical catheterization for gradual fetal fluid drainage, are described.