[The first manifestations of freemartinism in the calf fetus do not depend on XX/XY chromosomal chimerism].

In order to investigate the eventual role of XX/XY chimerism in freemartinism the vascular anastomoses between twin fetuses were surgically suppressed in litters with several fetuses, before the appearance of the first sexual anomalies. In three female fetuses isolated from their co-twins on days 37 and 45, the initial freemartin effect of gonadal and Müllerian inhibition was absent, in spite of an important XX/XY chimerism in the liver.