Freemartin

A freemartin or free-martin (sometimes martin heifer) is an infertile cow with masculinized behavior and non-functioning ovaries.

[7] Several researchers made the discovery that a freemartin results when a female fetus has its chorion fuse in the uterus with that of a male twin.

[11] The etymology of the term "freemartin" is uncertain: speculations include that "free" may indicate "willing" (referring to the freemartin's willingness to work) or "exempt from reproduction" (referring to its sterility, or to a farmer's decision to not bother trying to breed a freemartin, or both), or that it may be derived from a Flemish word for a cow which gives no milk and/or has ceased to be capable of bearing offspring;[5] "martin" is generally held to derive from an Irish or Gaelic word mart for "cow" or "heifer", although connections to Martinmas have also been posited.

If suspected, a test can be done to detect the presence of the male Y-chromosomes in some circulating white blood cells of the subject.

Genetic testing for the Y-chromosome can be performed within days of birth and can aid in the early identification of a sterile female bovine.

The freemartin model allows one to analyse perfectly healthy and unmanipulated animals, without resorting to transplantation often used in stem cell research.