Endometrosis is a chronic degenerative

syndrome A syndrome is a set of medical signs and symptoms which are correlated with each other and often associated with a particular disease or disorder. The word derives from the Greek σύνδρομον, meaning "concurrence". When a syndrome is paired ...

of the lining of the

uterus The uterus (from Latin ''uterus'', plural ''uteri'') or womb () is the organ in the reproductive system of most female mammals, including humans that accommodates the embryonic and fetal development of one or more embryos until birth. The uter ...

(the

endometrium The endometrium is the inner epithelial layer, along with its mucous membrane, of the mammalian uterus. It has a basal layer and a functional layer: the basal layer contains stem cells which regenerate the functional layer. The functional laye ...

) in mares. There are no explicit symptoms and the cause is also unknown, but the severity of endometrosis increases in parallel with the age and number of pregnancies of the mare. Endometrosis is confirmed by histological examination of an

endometrial biopsy The endometrial biopsy is a medical procedure that involves taking a tissue sample of the lining of the uterus. The tissue subsequently undergoes a histologic evaluation which aids the physician in forming a diagnosis. Medical uses There are a ...

, which shows degeneration of blood vessels in the endometrium, and fibrosis of the tissue, along with the development of endometrial cysts. The most common classification for endometrosis in mares was published by KENNY u. DOIG (1986) and modified by SCHOON et al. (1992). The different degrees of endometriosis are divided into stage I, IIA, IIB and III. These changes cause

subfertility Infertility is the inability of a person, animal or plant to Sexual reproduction, reproduce by natural means. It is usually not the natural state of a healthy adult, except notably among certain eusocial species (mostly haplodiploid insects). I ...

; in pregnant mares, the changes in the endometrium can cause the placenta to fail, leading to

miscarriage Miscarriage, also known in medical terms as a spontaneous abortion and pregnancy loss, is the death of an embryo or fetus before it is able to survive independently. Miscarriage before 6 weeks of gestation is defined by ESHRE as biochemical lo ...

of the foal. Foals which are delivered at full term may be underdeveloped (dysmature). No effective treatment is known. Since the causes of endometrosis are unsettled there is not known much about how to prevent it. The

etymology Etymology ()The New Oxford Dictionary of English (1998) – p. 633 "Etymology /ˌɛtɪˈmɒlədʒi/ the study of the class in words and the way their meanings have changed throughout time". is the study of the history of the Phonological chan ...

of endometrosis is from the

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

''endos'' (inside), ''metra'' (

womb The uterus (from Latin ''uterus'', plural ''uteri'') or womb () is the organ in the reproductive system of most female mammals, including humans that accommodates the embryonic and fetal development of one or more embryos until birth. The uter ...

) and ''-osis'' (

disease A disease is a particular abnormal condition that negatively affects the structure or function of all or part of an organism, and that is not immediately due to any external injury. Diseases are often known to be medical conditions that a ...

). This term was adopted in 1992; prior to that, endometrosis was variously known as chronic degenerative endometritis, endometrial fibrosis, or chronic endometrial disease.

Symptoms and Occurrence

There are no explicit symptoms, but suspicious are mares with low infertility or embryonic deaths. Endometrosis occurs most commonly in older mares or mares that have foaled at least twice, but in general all ages can be affected. However, there seems to be no relation between the occurrence or degree of endometrosis and the number of previous foalings. Also natural seasonal and cyclical changes in the endometrium seem to not affect the disease.

Causes and Pathogenesis

The causes of endometrosis are still unsettled. Most of the time endometrosis co-occurs with endometritis which may activate the periglandular fibrotic stroma cells, but it hasn't been proven. Endometrial periglandular fibrosis are the most common abnormalities that occur in mares with endometrosis. When the periglandular endometrial stromal cells look and function atypical it is a first sign for endometrosis. Mares who suffer from endometrosis seem to be unable to produce enough histotrophe, which leads to an embryonic loss of the foal.

Classification

The degree of endometrial fibrosis is classified by different systems based on histopathological examination. The most common is the classification by KENNY u. DOIG (1986) which was modified by SCHOON et al. (1992). The classification is divided into three or rather four stages (I,IIA,IIB,III) which consider degenerative endometrial changes based on degree of fibrosis, glandular alteration and glandular nests with or without periglandular fibrosis and glandular atrophy. The staging is influenced by different factors like taking a biopsy during or not during breeding season or histopathological examination after treatment against the endometritis which co-occurs most of the time.

Stages

The following table shows the different degrees of endometrosis which is classified by KENNY u. DOIG (1986) and modified by SCHOON et al. (1992).

Diagnosis

Endometrosis is most often diagnosed in barren mares. For the diagnostic procedure the endometrium of mares are biopsied to examine the changes in the endometrium under microscope. Therefore a small piece of tissue is removed from the endometrium of the mare, which is subjected to conventional histopathology. The only contraindication for endometrial biopsy is pregnancy.

Treatment

As the changes in the endometrium are seen as irreversible there is no effective treatment available. But to prevent infection antibiotics are administered in the uterus

Prevention and Prognosis

Since the causes of endometrosis are unsettled there is not known much about how to prevent it. But a good breeding management seems important to lower the chance of mares becoming endometrosis. Endometrosis is more common in mares that have been used irregularly for breeding. Also strict veterinary supervision increases the foaling rates of mares significally. As endometrosis is a chronic disease the mare will remain unfertile and the foal may be underdeveloped.

References

{{Reflist Horse diseases