For some Frame Overo is a highly desirable white pattern gene. All frame overo horses alive, carry a single inherited copy of the frame overo gene. This causes pigment loss hence white markings on certain areas of the horse. However, this gene is also linked to a fatal condition known as Lethal White Overo syndrome whereby a foal is born almost pure white in appearance, and dies within it's first 72 hours of life. Correct breeding can avoid this occurrence.
Lethal White Overo syndrome occurs when a horse inherits two copies of the for the Ile118Lys EDNRB mutation, one from both parents. Whereas (mentioned above) horses with just one copy of the gene will live normally and exhibit the desirable pattern. A horse with two copies of the mutated gene will suffer intestinal abnormalities, caused by undeveloped nerves of the foal's digestive system. These animals die within the first 72 hours of living and are typically euthanized sooner for humane reasons.
Frame Overo horses which carry just a single copy of the Ile118Lys EDNRB mutation, will pass one copy of it to their foals approximately 50%. Therefore, when breeding an overo horse to a solid non-overo horse, the foal can only inherit one copy. However, if two overo horses are bred together they could potentially BOTH pass the overo gene to the foal, meaning it inherits two copies. Horses which inherit two copies of frame overo will suffer the Lethal White condition. Therefore, proper mating must be carried out to ensure that two frame overo horses do not breed, cutting out the risk of the foal inheriting 2 copies of the gene.
Animal Genetics offers DNA testing for Frame Overo. The genetic test verifies the presence of the Ile118Lys EDNRB mutation, and presents results as one of the following:
|O/O||Homozygous||A lethal white foal which carries two copies of the frame overo gene would test as Homozygous for frame overo. No living frame overo horse more than a week old will test as being homozygous, it applies only to horses in the lethal white condition.|
|n/O||Heterozygous||Horse carries just a single copy of frame overo, therefore exhibits the desirable frame overo markings. Since frame overo is a dominant gene, the coat pattern should be present (depending on the absence of other).|
|n/n||Negative||Non-Overo or 'solid' horse|
Submit a Sample For Testing:
To submit a sample for testing please click on ORDER and download a sample submission form. Then follow the sample collection and submission instructions.
Cost per sample is £20. Please see our fee schedules below for bulk and combination rates.