Registry Services - Genetic Disorders
OLWS (Overo Lethal White Syndrome)

OLWS is a disorder in which the caecum, colon and sometimes the rectum undergo a large dilation and fill with faecal mass. Associated with homozygosity of the Frame Overo gene it results in incomplete migration of nerve cells to the large intestine during embryonic development. Affected foals die within 72 hours of birth.

At the direction of the Association all horses with white markings beyond the limits described in rule 8.1k will be required to be tested for the Frame or Overo Lethal White gene using the official procedure before they will be considered for registration in either the Stud Book or the Appendix Register.

Any horse applying for registration that displays excessive white markings, beyond the limits described in rule 8.1k, where both parents have a negative OLWS result on file with the Association, will not be required to be tested for OLWS.

Geldings who display excessive white markings beyond the limits described in rule 8.1k are not required to be tested for OLWS if parent validated to two (2) stud book quarter horses.

All horses applying for Foundation recording with the Association must be OLWS tested.

Any horses applying for Foundation recording that display excessive white markings, beyond the limits described in the rile 8.1k will not be accepted for Foundation stock recording.

Imported horses or horses applying for registration for Imported Semen must be OLWS tested if they display excessive white markings, beyond the limits described in rule 8.1k.

All horses tested for OLWS will have their registration or recording certificates marked with their OLWS official test results.