Horse-Breeding Problems: Pyometra

Infectious fluid in the uterus can mean poor future fertility for a broodmare.

A 19-year-old American Quarter Horse mare came to the clinic for evaluation of a vaginal discharge. The mare had given birth to eight foals in her lifetime, and the last foal was born five months prior to the clinic visit. The foaling was normal, and the mare was left open and not rebred. The goal of the exam was to determine the source of the vaginal discharge and provide a prognosis for future fertility. The mare was in good body condition for her age, and her external reproductive conformation was normal.

However, a yellowish-white purulent discharge was emanating from her vulva. An ultrasound examination revealed a dramatically enlarged uterus filled with “hyperechoic” or cloudy fluid. A vaginal speculum examination showed an inflamed, reddened cervix with a small amount of the purulent fluid passing out of the uterus through the cervix into the vaginal vault. Uterine culture, cytology and biopsy samples were collected for laboratory analysis. Culture revealed a heavy growth of Streptococcus bacteria and cytology evaluation showed large numbers of degenerated inflammatory cells (white blood cells) along with numerous chains of cocci-type bacterial organisms.

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Histopathologic evaluation of the biopsy sample revealed active, severe inflammation and moderate fibrosis and provided an overall biopsy score of 3B on a scale where 1 is considered normal and 3 is markedly abnormal. The clinical diagnosis of the mare’s condition was a pyometra, a chronic accumulation of a large volume of infectious fluid in the uterus. The mare was treated with a dose of prostaglandins, multiple uterine lavages, intrauterine antibiotics, systemic antibiotics, oxytocin and a Caslick surgery to close the dorsal aspect of her vulva. Re-examination three weeks later showed that the mare had no fluid present in her uterus. Pyometra carries a very guarded-to-poor prognosis for future fertility. The condition may be associated with a physical obstruction or functional defect in the cervix. Affected mares commonly have a persistent (ovarian) corpus luteum leading to inadequate prostaglandin production or release.

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A chronic or intermittent vaginal discharge may be present if the cervix is open. Conversely, if the cervix is closed or adhered shut, there may be no vaginal discharge despite accumulation of a large quantity of fluid in the uterus. Interestingly, mares with a pyometra are not usually systemically ill so there are no clinical signs such as fever, loss of appetite or depression to indicate that something is amiss. A key to management success is if the infection and concurrent fluid accumulation can be resolved and further accumulation prevented. This is largely dependent on the cervix’s ability to function properly. Mares with an incompetent cervix will usually reaccumulate fluid despite appropriate medical therapies or the condition will re-occur once therapy is discontinued. In those instances, further treatment is aimed at salvaging the mare for non-breeding purposes. The mare in the clinical case has a fair prognosis for future fertility based on the fact that she did not re-accumulate fluid in the three-week period between initial treatment and re-evaluation.