R300 Freemartinism

Freemartinism, also known as XX/XY Chimerism, is a form of intersex that occurs in cattle, resulting in a sterile, masculine heifer (freemartin or martin heifer). The phenomenon is caused by blood exchange between twin foetuses, a common occurrence in cattle pregnancies. In the case of a male-female set of twins, cells from the male with an XY genotype end up in the female’s (XX) system. This exposes the female to male developmental hormones, resulting in sterility and potentially abnormal genitalia and other sex characteristics.

Approximately 90% of male-female twin calves result in a freemartin. Since freemartinism is not always apparent on physical examination of the calf, a genetic test can be useful to identify them.