Bovine Freemartinism

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.