Context and significance
Endometritis is the most common infectious pathologic condition affecting the uterus in brood mares. Pathologic endometritis
is an abnormal extension of a physiologic process. In the pathologic form excessive inflammation of the endometrium occurs
and then persists. In an industry that often lacks a focus on profitability, it is a major cause of lower pregnancy rates
and poor reproductive efficiency. Mares that are prone to repeated pathologic episodes of endometritis are difficult to get
in foal and are called subfertile. Hughes and Loy (1969) emphasized the economic and opportunity costs of missed conception
and pregnancy. In this review the predisposing factors that culminate in endometritis, the pathogenesis of endometritis, the
principles of treatment and therapy for this condition will be discussed.
When advising clients on the attributes of high quality brood mares the age of the mare and her perineal conformation are
some of the most important characteristics. This is because the long term reproductive health of the mare depends on her ability
to maintain her reproductive tract with minimal contamination from genital pathogens. While other factors such as the mare's:
genetics, breed, pelvic conformation, immunologic constitution, reproductive history, and internal physical features such
as the vestibulovaginal sphincter, cervix, ovaries and uterus, all play a role, perineal conformation is commonly what is
at fault, and contributes to reduced fertility particularly as the mare ages.
Perineal conformation is very important for reproductive health. There should be a focus on the shape of the perineum and
tilt of the vulva of brood mares. The vulva should be vertical in its orientation and in line with the anus. The mare should
have 1/3rds of the vulva above the pelvic floor and 2/3rds below. In defective conformation the top of the vulva is recessed
inward and forms a slope down towards the anus. Opening the lips of the vulva should create a situation where air rushes into
the vagina. This is called pneumovagina or "wind sucking." Passage of a vaginal speculum should be met with resistance. The
physical barriers, such as the vulvar seal and the position of the vulva relative to the pelvic floor, prevent manure and
thus contamination from entering the reproductive tract. If these barriers are suboptimal the mare will have increased contamination
of the reproductive tract with genital flora and will be predisposed to infections such as bacterial endometritis. For example
pneumovagina is a common predisposing factor for endometritis, and is usually due to a conformational defect such as: abnormal
angulation of the vulva (so called tipped perineal conformation) or a defective vulvar shape or seal. In some mares one half
of the vulva will override the other half. Age: Older mares are over represented in the population of mares with pathologic endometritis.Age of the mare is important factor
because fertility begins to decline in mares after the age of 12. Age related deterioration in fertility in mares is often
linked to undesirable changes in the mare's anatomic barriers to infection, such as a sloping perineal conformation, the cumulative
toll of inflammatory and degenerative processes in the uterus, the aging of the immune system and a loss of competent oocytes.
The immune system of the mare ages in a process that has been referred to as "inflammaging." While veterinarians are able
to do many things in terms of reproductive management we are unable to make mares younger.
Breeds such as the Thoroughbred, where the focus is more on athletic than reproductive performance, and breeds with a narrow
genetic basis, such as the: Tennessee Walker, Clydesdale, Shire and Friesian are more prone to subfertility in both mares
Impaired physical barriers
In addition mares that have cervical injuries or that sustained injuries to the vulva, tumours of the reproductive tract,
endocrine disturbances, abnormal physiological responses (such as a long cervix that does not relax while in estrus), or a
dependent uterine location are prone to excess genital contamination due to impaired physical barriers. Recently a laparoscopic
procedure, uteropexy, was reported to help repair a pendulous uterus (Brink and Schumacher 2010).