CHAPTER 6Intrauterine Diagnostic Procedures
The character of the uterus is influenced by the reproductive status of the mare and the stage of the estrous cycle. Many of these changes are influenced by the presence of hormones. Dramatic changes occur during pregnancy and uterine involution. Thorough evaluation of the uterus is necessary to assess the status and predict the function of the uterus.
ANATOMY
The uterus has a single, relatively large uterine body and two uterine horns separated by a short septum at the bifurcation of the horns. The uterus is suspended in the broad ligament that is composed of smooth muscle and contains arteries, veins, lymphatic vessels, and nerves. The arteries supplying blood to the uterus are the uterine branch of the vaginal artery (caudal uterine artery), the uterine artery (middle uterine artery), and the uterine branch of the ovarian artery (cranial uterine artery). These three arteries form prominent anastomoses and contribute to arterial arches near the mesometrial attachment.1 The uterine veins follow a similar course relative to the uterine arteries. The uterine artery (middle uterine artery) is the largest uterine artery and the main supplier of blood to the uterus, whereas the main venous drainage of the uterus is via the uterine branch of the ovarian artery (cranial uterine vein). Interstitial fluid drains from the uterus through the lymphatic vessels and lymph glands to the thoracic duct that empties into the venous system near the heart. The uterus does not have sensory fibers and therefore does not require anesthesia locally for surgical biopsy. Pelvic nerves have parasympathetic fibers coming from the sacral area. Hypogastric nerves and the pelvic plexus supply sympathetic innervations from the caudal mesenteric ganglion that is located near the origin of the caudal mesenteric artery. These nerves join branches of the sacral nerves.2 The broad ligament is divided into indistinct regions defined by the part of the genital tract that it supports; the mesovarian supports the ovary, the mesosalpinx supports the oviduct, and the mesometrium supports the uterus. The uterus has several layers that from lumen to serosal surface include the luminal epithelium, endometrium composed of the stratum compactum and the stratum spongiosum, longitudinal muscle layer, circular muscle layer, and the perimetrium or serosal surface. Five to seven folds of endometrium are present in the collapsed uterus. These endometrial folds are arranged longitudinally and extend through the uterine body and cervix.
MARE RESTRAINT
The restraint necessary for most of the uterine diagnostic procedures that will be discussed in this chapter can be accomplished in most broodmares with simple standing restraint using a halter and lead shank. The horse handler should stand on the same side as the examiner, such that a left-handed examiner would stand to the right of the mare’s hindquarters and the handler at the mare’s head would also stand to the right or off side of the mare. Alternately, a right-handed examiner would stand to the left of the mare’s hindquarters and the handler at the mare’s head would stand to the left or near side of the mare. Positioning a mare in a stall doorway such that the body of the mare is against the wall of the stall and the hindquarters of the mare are just outside the door threshold may help keep a restless mare in position for the examination. The examiner can then stand behind the outside wall of the neighboring stall and reach over to the mare’s hindquarters. Fractious mares may be distracted with the use of a nose twitch. Palpation stocks can be used to contain mares and appear to offer some protection from kicks, but the examiner must remain alert because severe injury may be sustained should a mare suddenly squat or kick out with both hind legs. Fractious or anxious mares may require sedation if there is significant risk that the mare or examiner will be injured. A combination of acepromazine (0.02 mg/kg) and xylazine (0.6 mg/kg) administered intravenously often provides sufficient relaxation for an adequate length of time to ease examination. Lengthy procedures may require a longer-acting sedative such as detomidine intravenously (0.01 to 0.02 mg/kg).3 An attempt to assess the perineal conformation of the mare should be made before sedation, because the tranquilizers will dramatically relax the perineum, causing it to appear incompetent.
Palpation Per Rectum
Most mares are large enough to allow examination of the internal genital tract by palpation per rectum. The examiner should don a plastic shoulder-length examination sleeve and generously lubricate the forearm that will be used for the examination. Most commonly a nonsterile methylcellulose water-based lubricant is used. All feces must be removed from the rectum at the time of the internal examination. The uterine body is difficult to access adequately because it is bounded by the broad ligament. The entire length of each uterine horn should be systematically allowed to slip between the examiner’s opposing thumb and forefingers and a conscious note be made of the palpable presence of the endometrial folds. The endometrial folds should be palpable in the nonpregnant mare. The character of the pregnant mare’s uterine wall changes remarkably as early as 14 to 16 days after ovulation so that the endometrial folds are no longer palpable in the pregnant mare. A nonpregnant status must be confirmed before conducting any intrauterine procedures, because most intrauterine procedures would be detrimental to the maintenance of that pregnancy. The position of the uterus may be within the pelvic canal or cranial and/or ventral to the pelvic brim. The diameter of the horns should be estimated manually and the presence of any cysts, uterine fluid, or uterine masses noted. The tone of the anestrous uterus tends to be flaccid because steroid ovarian hormones are not present at this time. Progesterone present during diestrus will cause an increase in the tone of the uterus, resulting in a round, firm, tubular character of the uterine horns. During estrus the uterus tends to become edematous and have a plump but less turgid character. The cervix and ovarian structures should be assessed at the time of uterine palpation, and the character of these structures should be consistent with the character of the uterus and the stage of the mare’s estrous cycle.
Ultrasonography Per Rectum
Ultrasonography per rectum can be best used after complete and thorough palpation per rectum.4 All fecal material must be removed from the rectum during the examination. The footprint of the probe can be lubricated with nonsterile rectal lubricant. Upon entering the rectum with the ultrasound probe, one should locate the bladder and its neck because the urethra marks the caudal limit of the vagina. The presence of any material in the vagina (located dorsal to the bladder) should be noted. The cervix is not particularly distinct ultrasonographically. Each uterine horn should be systematically and consecutively examined in its entirety so that no portion of the uterus is overlooked. The diameter of each uterine horn can be measured ultrasonographically at its base. During estrus, edema of the endometrial folds appears hypoechoic and allows the folds to be seen more distinctly. A cross section of an estrous uterine horn has a spoked-wheel appearance because each fold projects towards the center or lumen of the horn. Although a very slight amount of anechoic uterine fluid may be seen in the uterine lumen during estrus normally, most accumulations of fluid not associated with pregnancy are considered abnormal and may be a clinical sign of endometritis. The character of uterine fluid may range from anechoic to quite hyperechoic. Unfortunately, there is not a direct correlation between echogenicity of the fluid and severity of the abnormality. Air mixed with uterine fluid, as seen in pneumometra, causes bright white lines or hyperechoic flecks in hypoechoic fluid. Equine urine is quite hyperechoic due to the urine crystals and mucus typically present. Therefore urine present in the uterus would appear hyperechoic. The uterine fluid associated with a hydrometra due to segmental aplasia of the tubular genital tract or a nonpatent hymen may appear anechoic. The fetal fluids seen in the pregnant uterus are black or anechoic during early gestation and are confined within the membranes of the conceptus.
Endometrial Microbiology—Aerobic Culture of an Endometrial Swab
It has been shown that the normal caudal genital tract has a considerable number of different microorganisms present, including microorganisms known to be significant uterine pathogens such as β-hemolytic Streptococcus zooepidemicus and Escherichia coli.5 Care must be taken to avoid harvesting microorganisms from the caudal genital tract (cervix, vagina, vestibule, clitoris) when procuring an endometrial swab. If examination or environmental conditions are not ideal, one may wish to perform the uterine swabbing while the mare is in estrus when uterine defenses (open cervix, increased cellular immunity) are optimal for dealing with iatrogenic contamination. Procurement of the swab during diestrus will allow detection of microorganisms that the mare was not able to eliminate on her own during estrus. Examination during diestrus also allows the examiner ideal conditions to thoroughly evaluate the mare’s cervix for presence of a competent canal or cervical laceration while the cervix is closed and under the influence of progesterone. The mare should be restrained so that procedures will be safe for the mare and the examiner as described in the section on palpation per rectum. In addition, swabs should be obtained in as clean an environment as possible. This can be challenging in a farm situation. Avoid dusty areas near hay storage and drafts.
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