Mare Problems in the Last Month of Pregnancy

Medical problems in the last month of pregnancy may have devastating effects on the foal or both the mare and the foal. This paper will review the most common medical complaints in the last month of pregnancy in the mare. A general overview of the evaluation of the colicky mare in advanced pregnancy is provided as a guideline for differentiation between genital and nongenital causes of colic. Diagnosis and management of specific genital causes of colic as well as some specific condition related to the reproductive tracts are discussed in detail.

1. Introduction

There has been substantial progress in the identification and management of high-risk pregnant mares in the last 5 years. Mares at risk of pregnancy loss include those with a history of medical or reproductive problems. Barren mares, old maiden mares, mares with cervical defects, and mares with recurrent pregnancy loss may all have difficulties in mid to late gestation. Mares with history of a medical or surgical problem that may be exacerbated by pregnancy including those with chronic cardiovascular or respiratory disease, gastrointestinal, metabolic, or endocrine disorders may also experience problems. Problems requiring immediate clinical evaluation to maximize foal and mare survival may also arise throughout pregnancy. It is important to communicate with owners on how previous and current disorders may adversely affect the mare’s pregnancy during the prebreeding examination.

Clients should be instructed to closely monitor pregnant mares. Parameters that are easy for clients to monitor are the general demeanor of the mare, feeding behavior, mammary gland development, and vaginal discharge. Vaginal discharge may be very discrete and should be suspected if the hair under tail is clumped. The major complaints during pregnancy can be grouped into the following: (1) colic; (2) abnormal vaginal discharge; (3) abnormal mammary development; (4) abnormal abdominal development or shape; and (5) accidents during the pregnancy.

This paper discusses the major disorders occurring in the last month of pregnancy, with special emphasis on the clinical diagnostic approach and referral protocols. Although the last month of gestation is defined as beginning around day 300, this can be variable because many physiological factors affect gestation length (breed of mare, breed of sire, season, nutrition, etc).

General Evaluation of the Colicky Pregnant Mare

The late pregnant mare is prone to colic, and the cause may be of gastrointestinal or genital origin.¹ Nonreproductive causes of colic include anterior enteritis, large colon volvulus, small intestinal incarceration, large colon impaction, tympany, small colon obstruction, and colitis.^1–3 Large colon volvulus occurs most commonly.^4–6 Colic causes of genital origin include first stage of labor, uterine torsion, uterine rupture, preparturient hemorrhage, and hydrops. Inguinal herniation or ruptured prepubic tendon should also be considered genital because they are induced by the heavy gravid uterus. Attaining a diagnosis of the cause of colic relies on a systematic approach including history, physical examination. and ancillary tests if needed. Approach to diagnosing the cause of colic in the late pregnant mare is a challenge because examination can be restrictive due to the large size of the uterus, particularly when performing transrectal palpation or abdominocentesis.

Historic data to include are the mare’s age, parity, stage of pregnancy (breeding date), previous colic episodes, previous surgery, response to analgesia, and degree and duration of pain. Management aspects to consider, especially for the hobby breeder, include changes in exercise, feeding, and water access. Colic signs vary in intensity from mild to severe. Some mares may show intermittent signs of discomfort, particularly after feeding. Underweight, malnourished, or stressed mares may be prone to developing gastric ulcers that may cause mild, often postprandial, colic. Other mares may go off feed intermittently, whereas some may be described as dull or reluctant to move. It is important to determine if there is a persistent tenesmus or violent colic because these cases may require immediate referral to a surgical hospital.

Physical examination should include heart rate, respiratory rate, capillary refill time, and auscultation of all abdominal quadrants. Mucous membranes should be evaluated for evidence of endotoxemia, presence of severe hyperemia, icterus, or paleness. Degree of dehydration should be estimated. The overall appearance of the mare (girth) and any abdominal distension should be noted. Late pregnant mares may not show a typical cardiovascular response to pain because they had several months to adapt to the demands of the growing fetus and placenta. Nasogastric reflux is always significant. Gastric distention can occur secondary to outflow obstructions, including extraluminal effects of displaced gastrointestinal viscera from the gravid uterus.

Transrectal evaluation of the abdominal content in advanced pregnancy presents a great challenge, even for experienced equine practitioners. In the case of violent colic, extreme caution should be exercised because mares can fall suddenly to the ground. The gravid uterus in the last month of pregnancy occupies the great majority of the abdomen, and displacement of some of the gastrointestinal tract is not uncommon.^1,7 Because of the enlarged uterus, many gastrointestinal structures cannot be palpated rectally, and absence of obvious palpable abnormalities does not rule out gastrointestinal pathology. Transabdominal ultrasonography should be performed on all mares to evaluate the gastrointestinal tract as well as the fetus and placenta.

The need for sedation depends on colic signs. Sedatives should be short-acting and rapidly cleared (xylazine or romifidine). The degree of rectal edema and amount and nature of fecal material in the rectal cavity must be evaluated. Mares may have a dry edematous rectum with thick mucus. Ample lubrication and local administration of lidocaine may help in the rectal examination. Epidural analgesia may also aid in rectal examination, but it must be considered carefully, particularly if referral is a possibility (ie, trailer ride). Primiparous mares may show recurrent signs of discomfort because of a large fetus. The first ruleout during transrectal palpation is uterine torsion. Mares with uterine torsion may show severe pain on palpation of the broad ligament (see below). An inability to advance the hand deep into the rectum may be due to hydrops allantois or large intestinal distension. Large intestinal distension is generally accompanied by severe straining. Palpation of distended small intestine warrants further evaluation for a nonstrangulating or strangulating/ischemic small intestinal lesion. Decision of medical or surgical treatment will depend on the amount of gastric reflux and peritoneal fluid character. Palpation of the large colon may reveal displacement or gas distention. Palpation of tight tenia (bands) across the pelvic inlet is a significant finding in colonic volvulus.

The most common large colon problems in the late pregnant mare include displacement, volvulus, impaction, and tympany.^1,3Although rare, mares with large colon volvulus typically have a history of acute onset of violent colic, cardiovascular compromise, and progressive abdominal distension. Gastric reflux is present in about one-third of the cases.³

Distention of the large colon, cecum, and small intestine may be a consequence of external compression by the fetus.⁸ Palpation of the cecum is severely hindered by the gravid uterus. Tight tenia are suggestive of gas accumulation caused by colonic obstruction or displacement. Cecal rupture should be considered in mares with signs of endotoxic shock and contaminated peritoneal fluid.

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