Physical Examination

The general health of the mare should be assessed, with special attention paid to body condition score (BCS). Poor BCS may accentuate an inadequate perineal conformation, which may favor certain uterine diseases, including endometritis. The latter may result from chronic bacterial contamination, which is favored by weakened physical barriers such as tilted vulva, sunken anus, and poor labia apposition. Splanchnoptosis describes the sinking of abdominal and pelvic organs to a lower position so that the muscles of the perineal body stretch cranially and pull the vulva into an inclined or horizontal position. The resulting inadequate perineal conformation predisposes access of fecal contaminants to the vagina and uterus. The “windsucker” test assesses the integrity of the vaginovestibular sphincter and is performed by gently pulling the labia apart and listening for the presence or absence of an inrush of air. Air rushing into the vagina denotes a weak vaginovestibular sphincter.

Palpation Per Rectum and Transrectal Ultrasonography

The veterinarian examining the mare should be familiar with the reproductive anatomy and function to be able to differentiate between physiologic and pathologic changes. Palpation of the cervix and assessment of its tone are very important because the cervical tone and, to a lesser extent, the uterine tone, are indicative of circulating levels of progesterone. Mares under progesterone influence during diestrus or pregnancy should have a closed cervix that feels tubular and firm on palpation per rectum.

During diestrus, the uterine horns are also readily palpable as distinct tubular structures. Once a careful and detailed palpation of the uterus has been performed, transrectal examination should be carried out using an ultrasound machine equipped with a 5-MHz linear transducer. The initial findings obtained from palpating the mare can be confirmed using transrectal ultrasonography. In addition to detecting specific ovarian structures that may confirm the stages of the estrous cycle (the presence or absence of corpus luteum or hemorrhagicum), ultrasonographic examination of uterine horns and cervix provides valuable information for determining the stage of the estrous cycle. In the cycling mare, diestrous uterine horns display uniform echogenicity, and the appearance of the uterine horns in cross section is fairly circular. On the contrary, estral uterine horns have a characteristic echogenicity that arises from uterine edema that results in a wagonwheel or starburst pattern. Ultrasonographic detection of uterine edema is consistently associated with low circulating levels of progesterone. It is very important to rule out pregnancy before proceeding with further examination of the reproductive tract.

Vaginal Examination

Vaginoscopy through a disposable speculum allows inspection of the cervix and vagina. Particular attention should be paid to the color, degree of moistness, adhesions, and any abnormal secretions in the vaginal floor or exiting the cervix. During estrus, the vaginal mucosa is moderately hyperemic and moist, reflecting increased vascularization and mucus secretion by the estrogenic cervix and uterus. The cervix is relaxed and may touch the vaginal floor, depending on the level of relaxation of the dorsal cervical ligament; the caudal cervical os displays variable degrees of relaxation. In diestrus, the vaginal mucosa is pale and dry, and the position of the cervix in relation to the vaginal floor is high; the dorsal cervical ligament is commonly observed in an extended position that suspends the cervix during progesterone influence. To avoid contamination, an endometrial swab for uterine culture should be collected before a manual vaginal examination is conducted. Digital examination of the vagina and cervix in the nonpregnant mare is very useful for detecting masses such as vaginal or perineal wall abscesses, hematomas, tumors, adhesions, or anatomic defects caused by dystocias and, most important, to assess the integrity of the cervix.

Uterine Swab for Culture and Cytology of Endometrial Cells

A sample for uterine culture is commonly collected with a guarded or double-guarded uterine swab. Once the endometrium is swabbed, the outer case of these guarded or double-guarded swabs can be manipulated to harvest endometrial cells for uterine cytologic examination. Endometrial brushes are now available in the United States, and they provide a better and more reliable way to harvest endometrial cells for cytologic evaluation. Cytologic examination of the endometrium is important because it corroborates laboratory culture results. Uterine culture and cytologic analysis are useful for identifying active acute endometritis caused by bacteria or fungal agents.

Endometrial samples for culture and cytologic examination also can be obtained by a low-volume uterine lavage (about 100 to 250 mL), which ensures sampling of a greater proportion of the uterine surface. A closed system is recommended for this procedure. It consists of saline solution in a plastic bag connected to a 32 to 34 French gauge silicone uterine catheter. The saline solution is allowed to flow into the uterus and by gravity is recovered back into the original bag. A sample for culture is aseptically drawn, and the remaining contents are centrifuged for cytologic evaluation.

Uterine flushes or swabs are best collected during estrus, because the mare’s uterine defense mechanisms are able to resist bacterial contamination at this stage of the cycle. If these procedures are conducted during diestrus, a luteolytic dose of prostaglandin F_2α is administered to induce estrus and minimize the chance that bacterial contamination will establish an infection.

Endometrial Biopsy

Endometrial biopsy yields information about inflammatory or degenerative changes affecting the endometrium. Pathologists classify these changes into four or five categories that are associated with the probability a mare will successfully carry a pregnancy to term and give birth to a live foal.

Hysteroscopy

In addition to enabling a direct viewing of the uterine lumen, hysteroscopy can be used for removal of foreign bodies (cotton-swab tips or uterine brushes) or fetal maceration remnants, biopsy of uterine masses, and laser-guided ablation of uterine cysts.

Bacterial Endometritis

The pathogenesis of bacterial endometritis in the mare is complex and has not been completely elucidated. Many mares that are not pregnant at the 14-day pregnancy check or that have early fetal loss do not have vaginal discharge. However, before and during the palpation per rectum, one should observe the vulva for exudate that might indicate uterine infection. Vaginal speculum examination may reveal variable volume of exudate at the external cervical os and on the cranial vaginal floor. Transrectal ultrasonography should always be performed to provide information about any abnormal uterine contents, especially if the mare is in estrus. The volume and echogenicity of intraluminal fluid should be noted. Detection of fluid during diestrus invariably indicates that the mare has active endometritis(Figure 169-1). Analysis of the mare’s cycling pattern may indicate shortened interestrous intervals induced by endogenous release of luteolytic prostaglandin F_2α (PGF_2α) from the inflamed uterus. Endometritis should be ruled out in mares that do not become pregnant after being properly managed, especially those that have distinct endometrial edema at pregnancy examination on days 12 to 14 postovulation.

Figure 169-1 Transrectal sonogram from a mare with intraluminal uterine fluid. Accumulation of intraluminal fluid in the uterus during diestrus, regardless of volume, should be considered pathologic and an indication of endometritis.

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