UC Davis School of Veterinary Medicine Veterinary Genetics Laboratory
Freemartin Testing - Sheep

A freemartin is defined as a female that is born as a twin with a male and is sterile as a result of exposure to masculinizing hormones. A connection between the two fetal circulatory systems develops early in gestation (anastomosis) and leads to the exchange of blood between the fetuses. Exposure to male hormones leads to underdevelopment of the female's reproductive tract. Incidence of freemartinism in sheep is generally low (about 1%), but increased risk has been observed when litter sizes are four or more. A DNA test that detects presence of Y-chromosome is available to confirm chimerism in the blood of females suspect of being freemartins.


Padula A. M. The freemartin syndrome: an update. Animal Reproduction Science 87: 93-109, 2005.

Allow 2-6 business days for results.

Veterinary Genetics Laboratory Tel 530-752-2211 Email VGL