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The term overo lethal white is used to describe a foal with two copies of the frame gene. It is born with a white coat and a malfunctioning colon. Foals with overo lethal white (OLW, also referred to as lethal white syndrome) will always die a painful death within 72 hours and are usually put out of their misery as soon as it's diagnosed. There is no remedy of any kind and it is not infectious. Careful breeding may prevent this illness.

Genetic cause

OLW is purely a genetic condition. That means it is not infectious and cannot spread in a herd or to people. It is caused when two horses with the frame pattern are bred together, and the foal receives both copies. As a result, the colon in the foal is not fully developed and the foal has a complete, or nearly complete white coat.

After birth, the foal has to eat on its own, but it is not capable of fully processing the food. As a result, the foal will die within 72 hours. There is no cure.

Before it is born, the foal can survive in uterus because it doesn't need its colon as long as it's still attached to the placenta. After birth, the umbilical cord is broken and the foal has to survive on its own. That's when the malfunction becomes apparent.

How to prevent

OLW is only caused when the foal inherits two copies of the frame gene. If a foal inherits only one copy, it remains perfectly fine, even if the coat is white due to some other gene. Therefore, it is best to never breed two horses with the frame pattern. Breeding with one horse that has the frame pattern is safe, but make sure you test both parents. Breeding with horses that do not carry frame, and do not belong to a breed that carries frame, is also safe.

Frame is present in a small number of breeds with an North American origin. These include the paint horsequarter horse and mustang horse. It's best to always test these breeds for frame before breeding them. You can find the test in the laboratory.

Be careful if you want to breed horses without testing them. Frame is cryptic and can appear as only a white blaze or snip. If you wish to breed with a horse that belongs to a breed that is known to have frame, always test both parents at the laboratory before breeding them. Never breed two horses that have frame.

European breeds like the Oldenburger, friesian, haflinger and many others are safe. If you're not certain and want to know if your horses are at risk before testing them, please post your question in the forum.

Healthy white foals

Sometimes, white foals are born that have not inherited two copies of the frame gene. These horses are perfectly fine and will likely grow up to become good horses. There are several genes that can cause this, and always keep this in mind. Not all white foals will die. It is always best to cancel any risks by carefully selecting the parents before breeding.

In Horse Reality

In this game all breeds are safe, except the quarter horse and the mustang horse.

Immediately after a foal with OLW is born, players will receive a message stating the condition has been found in their foal and that it will be put down. There is no fee, nor a cure.

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