Dr. van Haeringen Laboratorium B.V.

P902 Coat Colour Overo-factor (OLWS)


During the last decades, a large number of scientific publications have described the genetic principles of coat colour and coat variation. Coat colours and coat variations are influenced by many hereditary factors. The DNA-tests are based on physiological effects in the body, in which the production and distribution of pigments result in many coat colour variants. In several cases, the coat colour of an animal may only be decided using DNA-tests.

The Overo coat pattern is a white spotting pattern with white patches on the side with a “frame” of colour surrounding the white. A horse can also carry mutations for other modifying genes which can further affect its coat colour. While Overo coloured horses are desirable, the mutation that causes the overo colour is linked to a fatal condition known as Overo Lethal White Syndrome or OLWS. A foal with OLWS is born all- white and dies of complications from intestinal tract abnormalities. The Coat Colour Overo test (P902) tests for a genetic factor that affects the function of the EDNRB gene. This gene has two variants (alleles). The allele O is semi-dominant. One copy of the O allele results in horses with overo coat pattern. Two copies of the O allele result in a lethal white foal (OLWS). The allele N is recessive and does not have an effect on the basic colour.

Test specific information

This test is also included in a Combination Package Coat Colour.

Since 2015, two brands have been developed. CombiGen® is mainly directed at veterinarian applications, whereas CombiBreed® is mainly directed at breeders and/or owners.
Detailed information about Coat Colours and Coat Variation is presented at www.combibreed.com.


Most coat colours and coat types are usually visible directly after birth.

Turn Around Time

The turn-around-time of a test depends to a large extent on the logistics of sample transportation to the laboratory. After receiving the sample at the test location, you can normally expect the result within 10 working days. A longer delivery time applies to tests carried out by a Partner Lab.

Location of disease or trait

Genetic factors influencing coat colours and coat types are usually visible on the outside of an individual. Several factors may be hidden by the external variation.

Breed dependence

For this test samples from all breeds are accepted.

Sample type

For this DNA test we accept the following materials: Hair, Semen, Blood EDTA, Blood Heparin, Tissue. Please contact Dr. Van Haeringen Laboratorium if you wish to submit other material as listed.


Coat colours are based on many genetic factors. For each factor, a separate test result will be returned.


Various genetic factors influencing coat colour are inherited in a dominant or recessive mode. Coat colours are influenced by a large number of genetic factors.

Severity of Disease

Genetic characteristics are not a disease.

Code P902

Coat Colour Overo-factor (OLWS)

€ 47,80 (Incl. 21% VAT)
€ 39,50 (Excl. VAT)