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Abortion: mummification / maceration



  • Cause:
    • Mummification :
      • Occurs when intrauterine fetal death is followed by autolysis and absorption of fetal and placental fluids. The uterine contents remain sterile but become dehydrated. It typically occurs during the middle or last 1/3 of gestation. Mummification is not followed by abortion if there is a source of progesterone (eg a persistent corpus luteum, a viable feto-placental unit or an exogenous source), influencing the mare's uterus.
      • Mummification is almost universally associated with twin pregnancy in mares, where one fetus twin occupies most of the uterus and the second fetus occupies only the tip of one uterine horn dies due to lack of placental support and mummifies, and the remaining twin may have enough placental space to survive, at least temporarily.
    • Maceration :
      • Occurs when infectious agents access the uterus. The fetus becomes macerated and decomposes and is subsequently aborted.
  • Signs: premonitory signs of abortion OR delayed parturition if no viable fetus remaining.
  • Diagnosis: discovery of the mummified fetus upon examination of the abortus/examination of the fetal membranes at the time of parturition of the remaining twin survives until that stage of pregnancy.
  • Treatment: if the fetus(es) and membranes have been expelled, either prematurely or at term uterine lavage and antibiotic therapy.
  • Prognosis: variable.
  • Mummification and/or maceration of a single fetus is rare in the horse. Some case reports indicate chronic infertility following removal of a mummified fetus.
  • Mummification of one member of a set of twins happens occasionally during normal gestation and has no apparent significance in terms of reproductive capacity of the mare.



  • The reason for the death of an early embryo is obscure.
  • Mummification is usually associated with twin pregnancies in the mare.
  • When both conceptions survive into the fetal stage, the death of one fetus (the one with less placental space) probably occurs because the endometrial area is insufficient in terms of oxygen and nutrients to maintain twin conceptuses.
  • Some cases may occur when uterine torsion causes fetal death and then resolves spontaneously.
  • Rarely, a single mummified fetus may persist in a mare when fetal death in a sterile environment is followed by maintenance of high progesterone due to a persistent corpus luteum or an exogenous source of progesterone.
  • In some cases of mummification, fetal problems may cause dystocia Reproduction: dystocia.
  • Infectious and genetic causes of mummification are unknown in horses.


  • Typically, the mummified fetus is expelled with the survivor at its birth or abortion.
  • The fetal membranes become shriveled and dried until they resemble parchment and the fluids of the allantois, amnion and fetus are resorbed.
  • The uterus contracts on the fetus and molds into a dry, contorted mass.
  • Two kinds are distinguished by the appearance of the fetal membranes:
  • Papyraceous → both fetus and membranes undergo desiccation and the hard, gnarled fetus is surrounded by fetal envelopes which resemble parchment.
  • Hematic → a similar process to above takes place but between the uterus and chorion there is a peculiar adhesive substance, apparently derived from blood, which resembles melted chocolate.
  • When it (rarely) occurs in singleton pregnancies, a fetus may be retrieved which has either been undergoing mummification or is in a state of complete mummification.
  • When it occurs in twin pregnancies the death of one fetus is followed by its mummification, but the second fetus is not expelled at the time of the death of the first.
  • It is assumed that an equine mummy can exist only when there is a source of progestogen acting on the uterus, for example a viable co-twin, a persistent corpus luteum or an exogenous source.
  • It has been reported, that in fetal mummification and maceration little or no systemic involvement occurs (which is remarkable when related to the systemic condition of mares with retained placenta and severe metritis) → it most likely demonstrates an intact endometrium.
  • It is unknown whether mares with mummified fetuses are consistently anestrus.
  • Affected mares with macerated foals may experience variable cyclicity like mares with pyometra Uterus: pyometra.


  • A (rare) mummified singleton fetus is likely to be expelled when (if) systemic progesterone levels fall following its death.
  • A mummified twin fetus may not be expelled until its co-twin is either aborted or born.
  • If the cervix is open, the fetus and placenta may become infected and can undergo maceration/decomposition.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Pizzigatti D, Arévalo Batista F, Martins C F, Müller T R & Hussni C (2012) Hematic mummification in a mare with twin pregnancy. J Equine Vet Sci 32 (5), 305-308 SciDirect.
  • Threfall W R (2005) Singleton mummified fetus in a Standardbre mare. Equine Vet Educ 17 (5), 235-239 VetMedResource.
  • McCue P (1997) Fetal mummification in a mare. J Equine Vet Sci 17 (5), 267-269 SciDirect.
  • Barder A & Troedsson M H (1996) Mummified foetus in a mare. J Am Vet Med Assoc 208 (9), 1438-1440 PubMed.
  • Gilbert R O, Bosu W T, Levine S S & Smith D F (1989) Intrauterine death and onset of mummification of a single equine fetus. Equine Vet J 21 (4), 301-302 PubMed.
  • Roberts S J (1978) Twin pregnancy in a mare: a live foal and a mummified foteus. Cornell Vet 68 (2), 196-198 PubMed.

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