Freemartinism is a condition that can result from twinning of a heifer calf with a bull calf. It affects the heifer twin, and is characterised by an underdeveloped reproductive tract. The condition arises when the blood supplies of the two placentas of the twins merge together (anastomose) so that the calves share a common blood supply. The hormone responsible for development of the male reproductive tract (SRY hormone) becomes active before the hormones that regulate female reproductive tract development, and this hormone can transfer via the shared blood supply from the male to the female calf. The SRY hormone inhibits development of the ovaries, which in a normal calf go on to produce the hormones that promote development of the rest of the female tract. Freemartinism does not occur in every heifer calf born as a twin to a bull calf; approximately 10% heifer twins are not affected. It is also possible for an apparently single born calf to be a freemartin, if the calf was one of twins but the male twin died early in pregnancy.
- Female that never enters oestrus
- Small vulva
- Hypoplastic (small and underdeveloped) uterus, uterine horns and ovaries, and short vagina on rectal palpation
There is no treatment for freemartinism and affected animals are usually culled.