Bovine Freemartinism

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Aetiology

  • Results from sexual modification of a female twin by the in-utero exchange of blood from a male foetus.
  • Freemartin is XX genetic female, but becomes an XX/XY chimera.
  • 90% of female calves born co-twin to a male will be freemartins.
  • There are two theories to explain this:
    • Hormonal Theory
      • Hormones from the male twin reach the female through vascular anastamoses between the fused placentae to cause masculinisation of the female gonad.
    • Cellular theory
      • Exhange of blood-forming cells and germ cells between foetuses.
      • Reciprocal exchange results in identical erythrocyte antigen types and sex chromosome chimerism (60 XX/XY).
  • Paramesonephric (Mullerian) ducts do not form or atrophy.
  • Mesonephric (Wolffian) ducts persist in the female twin and may form rudimentary male tubular genitalia.


Diagnosis

  • Clinical genital abnormalities
  • Presence of sex chromatin bodies in circulating leukocytes of the male co-twin
  • Chimerism (XX/XY) of haematopoeitic cells. Blood tests can be used to demonstrate different chromosome complement in nucleated leukocytes and presence of two blood groups in each twin.
  • Rectal palpation and vaginoscopy reveal a shortened vagina
    • In calves 1-4 weeks old, the vagina is normally 13-15cm in length compared to 5-6cm in a freemartin.
  • Vulva and vestibule patent but vestibule or vagina is blind-ended - can be checked using speculum or probe.


Morphology

  • Gonads range from modified Ovaries to structures resembling Testes which are intra-abdominal and do not descend through the inguinal canal (Cryptorchid).
  • No spermatogenesis, sterile.
  • Produce Testosterone as the major hormone.
  • Rudimentary Uterus and Small Vagina.
  • Enlarged clitoris, long tufts of hair round vulva, skin fold from groin to umbilicus.
  • Vagina never communicates with uterus
  • Fibrous cords or non-patent uterine tubes.
  • Ovaries are usually small, cord-like thickenings in the ovarian ligament are semniferous tubules.