Things that go bump in the prepartum mare.

Pregnancy is not without its challenges.  There are several hazards the mare must avoid or overcome.  Rupture of and subsequent hemorrhage from the mid-uterine artery is the most common cause of death in mares post partum.  The external iliac artery, utero-ovarian artery, and uterine artery have also been implicated.1  Uterine contractions and obstetrical manipulations further increase stress on the vessel wall.2  Although usually considered a problem of the postpartum period, reports exist of cases in the peripartum period.1, 3  Peripartum hemorrhage has been reported to occur at any age, however older mares are considered to be at greater risk due to age-related degeneration of arterial vessels.4

Hemorrhage can occur into the peritoneal cavity, within the broad ligament of the uterus, within the uterine wall (mural hemorrhage), or into the uterine lumen.  Combinations of these may occur.  Hemorrhage into the peritoneal cavity leads to profound hypovolemia, pain and sometimes peracute death.  If confined to the broad ligament or uterine wall, pain can be significant but prognosis for life better.  Broad ligament hematomas may be incidental findings during routine reproductive examinations, or may become acutely apparent a variable time after foaling following rupture resulting in abdominal hemorrhage and pain.  Luminal hemorrhage is usually of less significance due to the relatively small amount of blood lost and lack of significant uterine distension.  Fractures of the pelvis are rare, however when they occur they may lacerate arteries or regional muscle bodies leading to significant hemorrhage into the surrounding musculature or peritoneal cavity.  Apparent abdominal pain can result from the fracture itself or the presence of peritoneal blood.  Hemoperitoneum itself is a significant cause of abdominal discomfort in the horse, with approximately 13% of all cases due to rupture of uterine vessels.5  Mare’s act colicky, sweat along the flanks, display flehmen, have elevated heart and respiratory rates, and mucous membranes become pale, dry and tacky.  How to manage is for another day.

Mild to moderate abdominal pain is also seen with torsion of the uterus.  This has been reported within the final three months of gestation, but is not usually associated with parturition.6-8  Devitalization of the uterine wall can lead to rupture and systemic illness.  Diagnosis is made by rectal palpation, with the broad ligament coursing tightly over the dorsum of the uterus indicative of the direction of torsion.  Hard to describe but once you have felt one you will know what I mean.  Ultrasonography can indicate health of the uterine wall and viability of the fetus.  Regrettably both can be devitalized.

It is rare to see uterine rupture prior to parturition, however perforation of the uterus can occur due to chronic stretch from an outstretched fetal hoof, or external abdominal trauma contacting the heavily gravid uterus in an area of pre-existing wall tension.  Systemic mare compromise will be present.

More likely to be seen are ruptured body wall, ruptured rectus abdominis, and prepubic tendon rupture causing an abrupt change in shape of the body wall.  Subcutaneous edema, fluid, hemorrhage and muscle fiber disruption are visible with ultrasonography.9  Prepubic tendon rupture results in ventral abdominal wall deviation, increasing regional edema and pain.  Hemorrhagic mammary secretions can occur.  Herniation of the abdominal wall has the potential to incarcerate gut.9.

These are just a few of the things that can happen.  Next time I’ll go over some things that can go wrong with the gastrointestinal tract around the time of foaling.

 

1.    Rooney J. Internal hemorrhage related to gestation in the mare. Cornell Vet 1964;54:11-17.

2.    Gruninger B, Schoon HA, Schoon D et al. Incidence and morphology of endometrial angiopathies in mares in relationship to age and parity. J Comp Pathol 1998;119:293-309.

3.    Pascoe RR. Rupture of the utero-ovarian or middle uterine artery in the mare at or near parturition. Vet Rec 1979;104:77-.

4.    Arnold CE, Payne M, Thompson JA et al. Periparturient hemorrhage in mares: 73 cases (1998-2005). J Am Vet Med Assoc 2008;232:1345-1351.

5.    Dechant JE, Nieto JE, Le Jeune SS. Hemoperitoneum in horses: 67 cases (1989-2004). J Am Vet Med Assoc 2006;229:253-258.

6.    Pascoe JR, Meagher DM, Wheat JD. Surgical management of uterine torsion in the mare: a review of 26 cases. J Am Vet Med Assoc 1981;179:351-354.

7.    Doyle AJ, Freeman DE, Sauberli DS et al. Clinical signs and treatment of chronic uterine torsion in two mares. J Am Vet Med Assoc 2002;220:349-353.

8.    Perkins NR, Robertson JT, Colon LA. Uterine torsion and uterine tear in a mare. J Am Vet Med Assoc 1992;201:92-94.

9.    Hanson RR and Todhunter RJ. Herniation of the abdominal wall in pregnant mares. J Am Vet Med Assoc 1986;189:790-793.

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