ISSN 2398-2977      

Reproduction: pregnancy diagnosis - indirect



  • eCG, previously known as pregnant mare serum gonadotropin (PMSG), is produced by fetal trophoblast cells that invade the maternal endometrium (endometrial cups) around days 35-38 after fertilization.
  • The cups increase in size until day 60 after which a maternal immunologic rejection results in a decrease in their size beginning around day 70 and continuing until day 120 by which time they are no longer functional.
  • Serum levels of eCG   Mare: physiology of pregnancy - diagram  mirror the growth and decline of the cups with first detection around day 35-40, peak at day 60-65, and decrease to non-detectable levels by day 120.
  • Used to confirm presence of live foal after 100 days.
  • However, eCG remains elevated once endometrial cups are formed even if there is fetal death.
  • In-house tests are available.


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Equine chorionic gonadotropin (eCG)
  • ELISA.
  • Mare immunologic pregnancy test (MIP test) hemagglutination inhibition test.
  • Direct latex agglutination test.

Estrogen determination

  • Serum conjugated estrogens ELISA method.
  • Urinary estrogens simple chemical method relying on color changes and fluorescence in the presence of warm concentrated sulfuric acid (Cuboni test).


  • RIA most specific for progesterone.
  • ELISA moderately specific.
  • Competitive protein binding assay least specific for progesterone.

Early pregnancy factor

  • Rosette inhibition test.


Equine chorionic gonadotropin (eCG)
  • Widely available.

Estrogen determination

  • Widely available.


  • ELISA - widely available.
  • RIA - specialist laboratory.

Early pregnancy factor

  • Not widely available.

Technique (intrinsic) limitations

Progesterone assay alone should not be used as a pregnancy test.

eCG can be elevated even after fetal death.

None of the above indirect methods can reliably detect multiple pregnancies.

Result Data

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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Crisci A et al (2014) Clinical, ultrasonographic and endocrinological studies on donkey pregnancy. Theriogenology 81 (2), 275-283 PubMed.
  • Ohnuma K et al (2000) Study of early pregnancy factor (EPF) in equine (Equus caballus). Am J Repro Immunol 43 (3), 174-179 PubMed.
  • Lofstedt R M (1997) Pregnancy diagnosis in the horse. Equine Vet Educ 9, 293-294.
  • Sobiraj A & Bostedt H (1985) Direct and indirect methods of the diagnosis of pregnancy in mares. Tierarztl Prax 13 (3), 313-323 VetMedResource.
  • Bostedt H, Hirschhauser R, Blanco C & Toth T (1983) Application of new latex test for indirect pregnancy diagnosis in mares. Berl Munch Tierarztl Wochenschr 96 (6), 192-194 PubMed.

Other sources of information

  • Metcalf E S, McCue P M & Jasko D J (2004) Evaluation of a Test for Equine Early Conception Factor. In: Proc 50th Ann Conv Am Equine. AAEP, Lexington, Ky. pp 518-520.


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