Some aspects of twin-gestation in the mare.
Abstract: A study has been made of 44 cases of twin pregnancy in mares. The fetuses, foals, fetal membranes and blood groups of parents and foals were examined in order to determine the incidence of chorio-vascular anastomosis, blood chimaerism and freemartinism. All of the twins proved to be dizygotic and 33 of the 34 pregnancies were bicornual. Fusion of the chorion was seen in 14 of 22 placentas and macroscopic choriovascular bridges were observed in five of these, although blood chimaerism was diagnosed in 11 of 25 cases (44 per cent) examined. This would indicate a high incidence of microchoriovascular anastomosis. The fetal female genital organs of four heterosexual twins were found to be anatomically and histologically normal at autopsy despite the existence of blood chimaerism. Five other sexvalley mature mares born as heterosexual twins with chimaerism all had normal genital organs and estrus cycles and one of these has since become pregnant. The important interspecies differences with respect to the incidence and degree of choriovascular anastomosis and freemartinism are stressed and suggestions for a plausible explanation were advanced.
Publication Date: 1970-07-01 PubMed ID: 4248640PubMed Central: PMC1319496
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Summary
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This research explores twin pregnancies in mares, investigating the incidence of various conditions including chorio-vascular anastomosis, blood chimaerism, and freemartinism. The results suggest a high prevalence of certain conditions but imply no negative impact on female fertility.
Study Overview
- The study analysed 44 instances of twin pregnancies in mares. Various aspects such as the fetuses, foals, fetal membranes, and the blood types of both parents and foals were examined to understand the occurrence of conditions including chorio-vascular anastomosis, blood chimaerism, and freemartinism.
Findings and Observations
- All twins were found to be dizygotic (or non-identical), and 33 out of 34 pregnancies were described as bicornual, a term for pregnancies with the embryos in separate uterine horns, suggesting independent and separate development.
- The examination of 22 placentas found that 14 displayed fused chorions, an outer membrane that envelops the fetus. Interestingly, in five of these placentas with fused chorions, choriovascular bridges, fusion of blood vessels between the fetuses, were observed.
- Despite the absence of visible choriovascular bridges in many cases, blood chimaerism — a condition where an individual contains two sets of cells with different genetic profiles — was diagnosed in 44% (11 out of 25) of the cases examined, suggesting a high incidence of microchoriovascular anastomosis (tiny shared or connected blood vessels between the fetuses).
Female Fertility and Chimaerism
- Intriguingly, despite the presence of blood chimaerism, the anatomical and histological examination (cell-level investigation) of the female genital organs of four of the heterosexual twins revealed them to be normal at autopsy.
- Five mature mares, born as heterosexual twins and showing blood chimaerism, all displayed normal genital organs and estrus cycles (cycles of fertility), with one even becoming pregnant later.
Implications and Conclusions
- This research highlights noticeable interspecies variations regarding the incidence and degree of choriovascular anastomosis and freemartinism (a condition where the female twin of a male-female pair is often infertile due to shared circulation and hormonal exchanges).
- The findings suggest that while chimaerism and chorio-vascular anastomosis occur frequently in the observed mare twin pregnancies, they do not appear to negatively affect the fertility of the female offspring.
Cite This Article
APA
Vandeplassche M, Podliachouk L, Beaud R.
(1970).
Some aspects of twin-gestation in the mare.
Can J Comp Med, 34(3), 218-226.
Publication
Researcher Affiliations
MeSH Terms
- Animals
- Animals, Newborn
- Blood Group Antigens
- Blood Vessels / anatomy & histology
- Cattle
- Diseases in Twins / embryology
- Diseases in Twins / epidemiology
- Diseases in Twins / pathology
- Diseases in Twins / veterinary
- Estrus
- Extraembryonic Membranes / anatomy & histology
- Female
- Fetal Death / veterinary
- Fetal Diseases / epidemiology
- Fetal Diseases / pathology
- Fetal Diseases / veterinary
- Freemartinism / epidemiology
- Genitalia, Female / pathology
- Gestational Age
- Hematologic Diseases / epidemiology
- Hematologic Diseases / pathology
- Hematologic Diseases / veterinary
- Horse Diseases / epidemiology
- Horse Diseases / pathology
- Horses
- Male
- Mosaicism
- Placenta / anatomy & histology
- Pregnancy
- Pregnancy, Animal
- Twins
References
This article includes 9 references
- Vandeplassche M, Spincemaille J, Herman J, Bouters R. [Twin pregnancy in the mare].. Dtsch Tierarztl Wochenschr (1946) 1965 Dec 1;72(23):541-8.
- Short RV. Reproduction.. Annu Rev Physiol 1967;29:373-400.
- Ashdown RR, Marrable AW. Adherence and fusion between the extremities of adjacent embryonic sacs in the pig.. J Anat 1967 Apr;101(Pt 2):269-75.
- Bruere AN, Macnab J. A cytogenetical investigation of six intersex sheep, shown to be freemartins.. Res Vet Sci 1968 Mar;9(2):170-80.
- Bruere AN, Fielden ED, Hutchings H. XX-XY mosaicism in lymphocyte cultures from a pig with freemartin characteristics.. N Z Vet J 1968 Mar;16(3):31-8.
- Merkt H. [Embryonic resorption and twin pregnancies in horses].. Berl Munch Tierarztl Wochenschr 1968 Oct 1;81(19):369-70.
- Vandeplassche M. The physiological explanation of split parturition in the pig and other mammalian species.. Ann Endocrinol (Paris) 1969 Mar-Apr;30(2):328-41.
- MAYER M, ANH JN, PANIGEL M. [ELECTRON MICROSCOPE OBSERVATION OF THE PASSAGE OF ERYTHROCYTES ACROSS THE WALL OF FETAL CAPILLARIES IN THE HUMAN PLACENTA].. C R Hebd Seances Acad Sci 1965 Apr 26;260:4605-6.
- Wyshak G, White C. Genealogical study of human twinning.. Am J Public Health Nations Health 1965 Oct;55(10):1586-93.
Citations
This article has been cited 1 times.- Soni V, Versoza CJ, Vallender EJ, Jensen JD, Pfeifer SP. Accounting for Chimerism in Demographic Inference: Reconstructing the History of Common Marmosets (Callithrix jacchus) from High-Quality, Whole-Genome, Population-Level Data. Mol Biol Evol 2025 Jun 4;42(6).
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