ENDOMETRITIS IN THE MARE
T.A.E. Stout
Department of Equine Sciences, Utrecht University, The Netherlands
[email protected]
Introduction
Unresolved endometritis is one of the most common reasons for failure to establish
or maintain pregnancy in an inseminated broodmare. A uterine infection can be
detrimental to fertility in a number of ways; firstly, if the infection is active, the
neutrophils recruited to combat the microorganisms are likely to bind and
phagocytose sperm introduced during insemination thereby reducing the likelihood of
conception. Secondly, persistence of a uterine infection beyond day 6-7 after
ovulation can interfere with pregnancy either by direct infection of the embryo as it
enters the uterine lumen, or because the associated inflammation triggers
endometrial PGF2a release leading to premature luteolysis. In the longer term,
persistent or recurrent uterine infections may lead to a disturbed uterine
environment, and instigate chronic degenerative changes in the endometrium that
compromise the ability to maintain pregnancy; however, the evidence that recurrent
infections result in chronic endometrial damage is currently lacking.
Diagnosis
In some instances, there are clear indications from a mare’s history (failure to
establish pregnancy despite mating with a fertile stallion at a number of cycles;
irregular cycle length) or from an initial gynaecological examination (vulval discharge;
cloudy uterine fluid; excess uterine oedema) that the uterus is inflamed and/or
infected. For a long time, the diagnostic cornerstone in the case of a suspected
uterine infection has been the use of a guarded endometrial swab to recover a
sample of uterine cells/mucus for microbiological and/or cytological examination.
However, there is increasing evidence that isolated culture or cytological examination
of material collected using a simple swab is not always sufficient to definitively
demonstrate the presence of pathogenic microorganisms. For example, E. coli
appears to stimulate a very modest neutrophil response (Leblanc, 2010), while a
swab can easily be contaminated with organisms from the caudal vagina or
perineum such that a positive culture alone is not definitive proof of an active
endometritis; for these reasons, it is sensible to consider the results of cytology and
microbiology in combination before drawing conclusions. Even then, small volume
uterine lavage and uterine bio psy both appear to deliver material that is more
sensitive and specific in the diagnosis of uterine infection.
Indeed, there is a growing body of opinion that some microorganisms are able to
avoid diagnosis during initial sampling using a guarded swab. Organisms suspected
to be capable of evading detection by swabbing include fungi/yeasts, which can
invade deeper into the endometrium (Stout, 2008). Recently, it has also been
claimed that Streptococcus equi zooepidemicus can exist in a dormant state deep in
endometrium (Morten Peterson; personal communication), and it has also been
suggested that organisms such as Pseudomonas aeruginosa may escape initial
detection by ‘hiding’ in discrete inactive colonies under ‘biofilms’ (LeBlanc, 2010). In
Proceedings
of
the
South
African
Equine
Veterinary
Association
Congress
2016
11