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Perineal and Cervical Abnormalities
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Part 1: Perineal Abnormalities
The perineum is the area that includes the anus, vulva, and the adjacent skin.
Vulva
In the normal mare, the vulva provides the first effective barrier to protect the uterus from ascending infection. The 'normal' mare has three functional genital seals forming a barrier between the external environment and the uterine lumen: the vulva, the and the cervix. During oestrus, the vulva and cervix relax, leaving the vulvovaginal constriction as the only seal.
The vulval lips should be full and firm and meet evenly in the midline with 80% or more of the vulval opening is below the brim of the pelvis. If the vulval seal is high (more than 4 cm of length dorsal to the pelvic floor) in relation to the pelvic brim, the vestibular seal is incompetent and aspiration of air (pneumovagina) and the aspiration of bacteria and contaminated material into the vagina can occur. The initial vaginitis may lead to cervicitis and acute endometritis resulting in subfertility. Contamination of the caudal reproductive tract with bacteria during pregnancy can result in embryonic death, and in late pregnancy can result in the development of placentitis and lead to abortion. Furthermore, the pneumovagina may lead o a urovagina (urine pooling within the vagina) when the vestibule and urethral opening are displaced cranially. The more severe conformational abnormalities are more likely to result in failure of the vulval seal, and to increased faecal contamination since the vulva forms a shelf on to which faeces may collect. The vulval lips may be angled at 25 or even 50 degrees to the vertical in these cases.
Caslick (1937) first pointed out the importance of this condition in relation to genital infection in Thoroughbred mares. Interestingly, it is most commonly found in Thoroughbreds, and, in the author's experience, is almost unknown in Shires and native ponies.
Defective vulval conformation can be (1) congenital, which is very rare or (2) acquired, which is due to (a) vulval stretching following repeated foalings, (b) injury to perineal tissue or (c) poor bodily condition (old, thin mares).
Older, pluriparous mares are more commonly affected with pneumovagina (aspiration of air into the vagina). However, young mares that are in work and have little body fat and/or poor vulval conformation, can also develop pneumovagina. In some mares, pneumovagina may only occur during oestrus when the perineal tissues are more relaxed. Some mares make an obvious noise whilst walking, but in other mares the diagnosis may be more difficult. The presence of hyperemia and a frothy exudate in the anterior vagina on examination with a speculum is pathognomic. Rectal palpation of a ballooned vagina or uterus from which air can be expelled confirms the diagnosis. Real-time ultrasound examination of the uterus may reveal the presence of air as hyperechoic (white) foci sometimes seen as a line at the opposed lumenal surfaces. Cytological and histological examination of the endometrium may demonstrate significant numbers of neutrophils indicative of an endometritis. Rarely eosinophils are also found in association with vaginal windsucking. Pascoe (1979) describes a Caslick Index (slope of vulva x length of vulva) which assists determination of the need for corrective surgery. This Index is particularly useful in mares not showing classical signs of pneumovagina. [...]
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