The wide variance in anatomical characteristics among heifers born co-twin to a bull
make diagnosis of freemartinism by measurements of vaginal length or the distance between the
anus and vulva unreliable. Change in serum luteinizing hormone (LH) in response to injection
of estrogen or gonadotropin releasing hormone (GnRH) is different in freemartins compared
to normal heifers but is also an unreliable predictor of freemartinism. Presently, the most
conclusive way to establish freemartinism in a heifer born co-twin to a bull is to measure the
percentage of XX and XY chromosomes in cells from whole blood, which is a specialized and
expensive procedure.
