History

A 6-year-old 500-kg (1,100-lb) multiparous Thoroughbred broodmare was referred to our veterinary hospital 3 days after parturition because of signs of colic; the mare was accompanied by its 3-day-old foal. The farm manager reported that parturition had been uncomplicated and that the mare had appeared to be comfortable until the day of referral; the referring veterinarian reported that the fetal membranes appeared to have been expelled in their entirety after parturition.

At the time of admission, results of physical examination were unremarkable, except for pale pink mucous membranes. Results for a CBC and venous blood gas analysis were within reference limits. Serum biochemical analysis revealed an elevated creatine kinase activity (1,720 U/L; reference range, 10 to 350 U/L). The lactate concentration was high (5.1 mmol/L; reference range, 0.5 to 1.78 mmol/L). The PCV was within reference limits (39%; reference range, 27% to 43%). Total protein concentration was at the low end of the reference range (4.7 g/dL; reference range, 4.6 to 6.9 g/dL).

Transabdominal ultrasonography with a 2- to 5-Mhz curvilinear probe^a revealed a moderate amount of swirling peritoneal fluid containing hyperechoic particles in the ventral portion of the abdomen. The appearance of this free fluid was consistent with that of blood during acute hemorrhage.

Hemorrhage from the uterine artery was considered to be the most likely cause of the colic. A catheter was placed in the left jugular vein, and isotonic solution^b was administered at a maintenance rate of 1.5 L/h. In addition, aminocaproic acid (loading dose, 40 mg/kg [18.2 mg/lb] in 1 L of lactated Ringer solution, followed by a maintenance dose of 20 mg/kg [9.1 mg/lb] in 1 L of lactated Ringer solution, q 6 h for a total of 4 doses) and flunixin meglumine (1.1 mg/kg [0.5 mg/lb], IV, q 12 h) were also administered. Serial measurement of PCV and total protein concentration was performed, which revealed a decrease in PCV of 12% and a decrease in total protein concentration of 0.3 mg/dL over a 12-hour period. At that time, a transfusion of 8 L of whole blood was administered. The dosage of flunixin meglumine was reduced (0.5 mg/kg [0.23 mg/lb], IV, q 12 h) at 24 hours after the blood transfusion, and IV fluids were discontinued at that time.

The mare became febrile (rectal temperature, 39.3°C [102.7°F]; reference range, 37.2° to 38.3°C [99° to 101°F]) 36 hours after the blood transfusion. Another CBC was performed, which revealed neutrophilia (8,740 cells/μL; reference range, 2,500 to 6,900 cells/μL) and lymphopenia (1,130 cells/μL; reference range, 1,500 to 5,100 cells/μL). Treatment with trimethoprim-sulfamethoxazole (30 mg/kg [13.6 mg/lb], PO, q 12 h) was initiated, and an additional dose of flunixin meglumine (0.5 mg/kg, IV) was administered.

Transrectal palpation and ultrasonography with a 5-Mhz linear probe^c of the reproductive tract were performed. The uterus was toned and had palpable rugae; the left and right uterine horns were asymmetric, with the left being larger than the right. Ultrasonography revealed a large hematoma in the broad ligament of the left uterine horn. A distinct hyperechoic multilayer elliptical structure (approx 1 cm in height × 5 cm in length) in the uterine body was surrounded by anechoic fluid containing flocculent debris (Figure 1).

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Ultrasonographic image of the uterine body of a mare that was examined 3 days after parturition because of signs of colic. The hyperechoic multilayer elliptical structure is approximately 1 cm in height by 5 cm in length.

Citation: Journal of the American Veterinary Medical Association 252, 6; 10.2460/javma.252.6.655

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Question

What is the structure in the uterus visible on the ultrasonographic image? Please turn the page.

Answer

The ultrasonographic appearance is consistent with that of a hippomane.

Results

After transrectal ultrasonographic evaluation was completed, the mare's tail was wrapped and the perineum was cleaned in preparation for palpation of the uterus per vagina. The structure in the uterus was manually extracted and identified as a hippomane, which was covered in a mucoid film (Figure 2). The uterus was lavaged with approximately 16 L of dilute (1%) betadine solution divided into boluses of 3 to 4 L/bolus, which were sequentially infused into the uterus and removed via siphoning until the effluent was clear.

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Photograph of the hippomane that was manually removed from the uterus of the mare in Figure 1. Notice that it is covered in a mucoid film.

Citation: Journal of the American Veterinary Medical Association 252, 6; 10.2460/javma.252.6.655

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Within 12 hours after removal of the hippomane and uterine lavage, the mare was afebrile. Transrectal palpation and ultrasonography of the reproductive tract the following morning revealed no evidence of free intrauterine fluid or any other abnormalities. The mare had no additional episodes of pyrexia.

Discussion

The mare of the present report was initially examined because of colic-like behavior 3 days after parturition, with acute hemorrhage (likely from the uterine artery) as the diagnosis. The mare became febrile while hospitalized. Potential causes of pyrexia in a postpartum mare include peritonitis, metritis, retained fetal membranes, or trauma associated with parturition.¹ In this case, there was no history or visible evidence of trauma, which decreased the likelihood of a perineal laceration, rectovaginal fistula, vaginal laceration, or vaginal abscess as the cause of pyrexia.

Diagnostic evaluation of fever in a postpartum mare should include examination of the reproductive tract.² Transrectal palpation of a postpartum uterus allows assessment of uterine size and tone, whereas ultrasonography allows for evaluation of the uterine lumen and its contents.² Ultrasonography may reveal excess uterine fluid, flocculent debris, and the presence of retained fetal membranes, which appear as discrete hyperechoic structures within the uterine lumen.³ Transvaginal palpation of the reproductive tract may aid in the identification of uterine tears, fetid uterine fluid, or fetal membrane fragments.²

In mares with a history of uterine artery hemorrhage, many clinicians will limit the amount of palpation per rectum to avoid the possibility of disrupting formation of a thrombus.^1,2 However, when the mare of the present report became febrile, identifying the source of the fever necessitated assessment of the reproductive tract via transrectal palpation and ultrasonography, despite the risk of potential clot disruption. At the time of the reproductive evaluation, the PCV and total protein concentration had been stable for 24 hours, which suggested that there was no active hemorrhage. In addition, precautions were taken to minimize excitability and stress of the mare during the examination. The mare was positioned in the door of the stall so that her head was facing into the stall, and the foal was restrained and positioned near the mare's head. Transrectal palpation, ultrasonography, and uterine lavage were performed cautiously but expediently to minimize the duration of the examination.

Results of the examinations confirmed a uterine artery hematoma, which made it less likely that there was bleeding and secondary peritonitis attributable to a uterine tear or other trauma. Ultrasonographic examination revealed a distinct multilayer hyperechoic elliptical structure surrounded by an accumulation of mixed echogenic fluid within the lumen of the uterine body. The presence of the hyperechoic structure, in conjunction with the pyrexia and hematologic changes, was suggestive of a differential diagnosis of metritis secondary to retained fetal membranes.

Foaling trauma and retained fetal membranes are precursors to the development of metritis, but it is important to mention that metritis may also develop in clinically normal postpartum mares that are confined to a stall for prolonged periods.⁴ Mares that are confined to a stall have reduced uterine clearance, which results in excessive accumulation of uterine fluid, and are at risk of developing metritis.⁴

It is likely that the uterine tone and contractility of the mare described here were initially reduced for a period because of hemorrhage from the uterine artery. When these factors were combined with stall confinement to facilitate medical treatment of the hemorrhage, this may have further reduced uterine clearance, which resulted in retention of the hippomane and development of metritis.

Treatment for metritis includes the use of systemically administered broad-spectrum antimicrobials, ecbolics, antiendotoxic and anti-inflammatory agents, and uterine lavage.⁵ Supportive care, including administration of IV fluids and treatments directed at preventing laminitis, may be initiated in severe cases.³ For mares that are confined to a stall, oxytocin administration and large-volume uterine lavage are warranted to reduce the incidence of metritis.⁴ Because of the lack of exercise, uterine clearance and the evacuation of normal lochia are decreased in mares that are confined to a stall.⁴ In the mare described here, administration of trimethoprim-sulfamethoxazole (a broad-spectrum antimicrobial) was initiated when the mare was first noted to be febrile, and administration was continued for 5 days. Oxytocin was not used because of the potential for thrombus disruption associated with cramping, discomfort, and an increase in heart rate and blood pressure in mares with periparturient hemorrhage.²

In the mare described here, palpation of the uterine lumen per vagina was performed to enable us to further investigate and identify the hyperechoic structure detected during ultrasonography. The hippomane was manually removed, and the uterus then was carefully lavaged to evacuate lumen contents and reduce the bacterial load. To ensure that we did not overly distend the uterus and risk disruption of the clot, 16 L of dilute betadine solution divided into boluses of 3 to 4 L/bolus was sequentially infused into the uterus and removed via siphoning.

Examination of the fetal membranes is a routine part of a postfoaling examination directed at determining that the chorioallantois has been completely expelled. However, it is important to mention that in addition to the chorioallantois, other clinically normal features of the equine fetal membranes and uterine contents include the amnion, allantoic vesicles, allantoic pouches, hippomanes, amniotic plaques, and yolk sac remnants.⁶ A hippomane is a soft proteinaceous concretion found within the fetal fluid in the allantoic cavity in all mares.⁶ Hippomanes are typically expelled during parturition or shortly thereafter along with the fetal membranes and other uterine contents.

To the authors' knowledge, there have been no reports of retention of a hippomane in a mare for 3 days after parturition and concurrent development of metritis. The mare described here served as an example of the importance of considering a retained hippomane as a differential diagnosis for retained fetal membranes as well as a reminder that confining a postpartum mare to a stall may increase the likelihood of the development of metritis. A febrile episode in a postpartum mare should warrant investigation of the reproductive tract as a potential source of the fever.

Outcome

The mare was discharged to the care of the farm personnel 6 days after admission. It was recommended the mare should not be bred for at least 90 days after parturition or until the hematoma in the broad ligament had resolved. The mare did not have any reproductive complications after discharge from the veterinary hospital. The mare was bred 77 days after discharge and conceived.