Lethal white syndrome in overo horses, also known as overo lethal white syndrome (OLWS), is a genetic disorder that affects foals born with certain coat patterns. These foals appear healthy at birth but suffer from a non-functioning colon, leading to severe colic and death within a few days. Understanding this condition is crucial for breeders and horse enthusiasts to make informed breeding decisions.
What Causes Lethal White Syndrome in Overo Horses?
Lethal white syndrome is caused by a genetic mutation in the endothelin receptor B (EDNRB) gene. This mutation is associated with the overo coat pattern, a type of pinto coloring characterized by irregular white patches. When two horses carrying the OLWS gene are bred, there is a 25% chance their foal will inherit two copies of the mutated gene, leading to the syndrome.
How Does Lethal White Syndrome Manifest?
Foals with lethal white syndrome are born with a predominantly white coat and blue eyes. Despite appearing normal initially, they lack nerve cells (ganglia) in their intestines, preventing normal bowel movements. This results in severe colic, as the foal cannot pass waste, leading to death within 72 hours if not euthanized.
What is the Genetic Risk of Breeding Overo Horses?
Breeding two overo-patterned horses increases the risk of producing a lethal white foal. Here’s a breakdown of potential outcomes:
- 25% chance of a lethal white foal (homozygous for the mutation)
- 50% chance of a healthy carrier foal (heterozygous for the mutation)
- 25% chance of a non-carrier foal (no mutation)
How to Prevent Lethal White Syndrome?
To prevent lethal white syndrome, breeders can perform genetic testing on their horses. Testing identifies carriers of the OLWS gene, allowing breeders to avoid mating two carriers. This strategy significantly reduces the risk of producing affected foals.
Genetic Testing for OLWS: How Does It Work?
Genetic testing for OLWS involves a simple DNA test. A sample, typically a hair or blood sample, is collected from the horse and sent to a laboratory for analysis. Results indicate whether the horse is a carrier of the OLWS gene, helping breeders make informed decisions.
Why is Genetic Testing Important?
- Identifies Carriers: Detects horses that carry the OLWS gene.
- Informed Breeding: Helps breeders avoid mating two carriers.
- Reduces Risk: Lowers the chance of producing a lethal white foal.
People Also Ask
What is the Overo Coat Pattern?
The overo coat pattern is a pinto coloring with irregular white patches that do not cross the back between the withers and tail. This pattern is common in breeds like the American Paint Horse.
Can Lethal White Syndrome Be Treated?
Unfortunately, there is no treatment for lethal white syndrome. Affected foals suffer from severe gastrointestinal issues and typically do not survive beyond a few days without euthanasia.
Are All White Foals Affected by Lethal White Syndrome?
Not all white foals have lethal white syndrome. The condition specifically affects foals with the OLWS genetic mutation. White foals without this mutation can be healthy.
How Can Breeders Avoid Lethal White Syndrome?
Breeders can avoid lethal white syndrome by conducting genetic testing on breeding horses and avoiding mating two carriers of the OLWS gene.
What Other Conditions Are Related to Coat Patterns in Horses?
Other genetic conditions related to coat patterns include hyperkalemic periodic paralysis (HYPP) in horses with the impressive bloodline and hereditary equine regional dermal asthenia (HERDA) in Quarter Horses.
Conclusion
Lethal white syndrome is a serious genetic disorder affecting overo-patterned horses. Through genetic testing and informed breeding practices, the risk of producing affected foals can be minimized. Breeders and horse enthusiasts must understand this condition to ensure the health and well-being of their horses. By making informed decisions, they can contribute to the overall health of the equine population.
For more information on horse genetics and breeding practices, consider exploring topics such as the genetics of coat color in horses and equine genetic testing services.