Freemartinism in a captive herd of Rocky Mountain bighorn sheep (Ovis canadensis).

Freemartinism in two animals from a captive herd of Rocky Mountain bighorn sheep (Ovis canadensis) at the Denver Zoological Gardens (Denver, Colorado, USA) is described. A young ewe had female external genitalia, a masculine appearance, and demonstrated male behavior as she matured. Another ewe with female external genitalia died as a yearling. Necropsy revealed a non-patent vagina and internal male genitalia. Both females were chimeric with karyotypes containing XX and XY sex chromosomes.