Introduction: In mammals, ovarian carcinomas are reported
commonly in dogs and arise from the surface epithelium of the ovary
or from the rete ovarii. In horses, they occur rarely. A 6-year-old
quarter horse mare was diagnosed during gynaecological examina-
tion with an enlarged right ovary. Laparoscopic ovariectomy was
performed in November 2012. Histopathological examination showed
a highly malignant carcinoma infiltrating the right ovary. The condi-
tion of the horse improved until April 2013 when the animal devel-
oped fever, anorexia, anaemia, neutrophilia and monocytosis.
Ultrasound examination revealed a large amount of abdominal fluid
and a large, heterogeneous mass in the cranioventral abdomen. The
mare was humanely destroyed.
Materials and Methods: Full post-mortem examination, histology