What is another word for freemartins?
Pronunciation: [fɹˈiːmɑːtˌɪnz] (IPA) 
In biology, a freemartin refers to a female mammal that is sterile at birth and is always a twin to a male. There are several synonyms used to describe such individuals, including a nulliparous female and a sterile heifer. Nulliparous refers to an animal that has never given birth, while a heifer is a young female cow that has not yet given birth to a calf. Another synonym for freemartins is a mixed-sex twin, which is self-explanatory and describes the circumstance in which the individual is a female twin to a male sibling. These synonyms are used in veterinary and biological circles to describe freemartins, which is a relatively uncommon phenomenon in the animal world.
