MORE ABOUT LETHAL WHITE FOAL SYNDROME

To be an overo horse, a horse must inherit ONE overo gene from one of its parents. If the horse inherits this overo gene it is then able to pass the gene on to its offspring...   ANY horse with the overo gene - no matter how much or how little white the horse has, has an equal chance of producing overo foals... the amount of white on an overo does NOT indicate a stronger or weaker ability to pass the gene to its offspring.

Not certain? :) lets look at one of the "famous" overo sires "Rowdy".  A bay stallion with a blaze, he is responsible for a great many overo breeding programs today.

An overo has ONE overo gene and ONE non-overo gene... so it can pass either on to its foals...

The following table will show exactly what sort of foal is possible when crossing an overo with a non-overo:
In this case the dam is a non-overo (two negatives) and the sire is the overo (one negative, one positive)

As you can see by crossing an overo horse with a non-overo horse you will have a 50% chance of an overo foal and a 50% chance of a non-overo foal.
Please note - the overo foal MAY or MAY NOT have a lot of white - but it WILL carry the overo gene. 

The second table shows the possible results of crossing two overo horses:

So by crossing TWO overo horses we STILL have a 50% chance of an overo foal... but now instead of a 50% chance of a non overo, it is 25% non-overo and 25% lethal white.

From these two table was can see that breeding two overos together DOES NOT increase your chances of a healthy overo foal and it does NOT increase the amount of overo pattern the foal will receive.

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