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Endometrosis is a chronic degenerative syndrome of the lining of the uterus (the endometrium) in mares.[1] The cause is unknown, but the severity of endometrosis increases in parallel with the age and number of pregnancies of the mare.[2] Endometrosis is confirmed by histological examination of an endometrial biopsy, which shows degeneration of blood vessels in the endometrium, and fibrosis of the tissue, along with the development of endometrial cysts.[2] These changes cause subfertility;[1] in pregnant mares, the changes in the endometrium can cause the placenta to fail, leading to miscarriage of the foal.[2] Foals which are delivered at full term may be underdeveloped (dysmature).[3] No effective treatment is known.[3]

The etymology of endometrosis is from the Greek endos (inside), metra (womb) and -osis (disease).[1] This term was adopted in 1992;[4] prior to that, endometrosis was variously known as chronic degenerative endometritis, endometrial fibrosis, or chronic endometrial disease.[4]


  1. ^ a b c Hanada, M; Maeda, Y; Oikawa, MA (2014). "Histopathological characteristics of endometrosis in thoroughbred mares in Japan: results from 50 necropsy cases". Journal of Equine Science. 25 (2): 45–52. doi:10.1294/jes.25.45. PMC 4090358. PMID 25013358.
  2. ^ a b c Sprayberry, Kim A (2009). "Chapter 20: Fetal monitoring in broodmares". In Samper, JC (ed.). Equine breeding management and artificial insemination (2nd ed.). St. Louis, Missouri: Saunders/Elsevier. pp. 241–248. ISBN 9781416052340.
  3. ^ a b Munroe, G; Campbell, M; Munroe, Z; Hanks, M (2011). "Chapter 2.1: Female reproductive tract. Chronic degenerative endometrosis". In Munroe, GA; Weese, J. Scott (eds.). Equine clinical medicine, surgery, and reproduction. London: Manson Publishing/The Veterinary Press. p. 318. ISBN 9781840766080.
  4. ^ a b Flores, JM; Rodríguez, A; Sánchez, J; Gómez-Cuétara, C; Ramiro, F (April 1995). "Endometrosis in Mares: Incidence of Histopathological Alterations". Reproduction in Domestic Animals. 30 (2): 61–65. doi:10.1111/j.1439-0531.1995.tb00606.x.