HGG Community Forums

White 1 (Kit W) which is what the mare has, and white 2 (Kit W2), which is what the stud has, are a very risky combination. It’s very likely to produce a lethal foal when bred to each other.

Here is a link to the lethality chart for the kit genes.

http://hj2.huntandjump.com/forum/discussion/13757/new-kit-lethality-and-kit-mutation-load-explained#Item_12

That said, the foal is only lethal if it inherits both patterns and has a high enough white factor. Each parent has a 50% chance at passing on their white allele, so there is only a 25% chance the foal would get both. And even if it did get both, there is still a possibility for a live foal, depending on white factor. Try to breed for a white factor of "none" or "minimal". With 1 parent "none" and one "light", and no other patterns that influence white factor, I personally would have no issue breeding this pair.

Can someone please explain what Lethal foal means?

Okay. The teacher in me wants to make a more thorough explanation. If this seems too complicated, I will not be offended if you decide to stop reading here. :D

There are three mechanisms which cause a foal in the game not to survive.

1. If it inherits the Frame Gene from both parents. That gene is abbreviated Olw in the game, which stands for Overo, Lethal White, which is where the phrase Lethal Foal comes from. What the dominant Olw broken gene does is cause a foal to be forn with an incomplete digestive system and all white hair. Because it can't digest it's food, it will die from impaction colic within a day or so of birth, a difficult and tragic end of careless breeding. The Olw gene, combined with other white-producing genes gives the typical "Overo" pattern of paint horses. However, a horse without a significant white producing gene can carry Frame without showing it. This is one reason to color test all horses that might possibly carry the gene. In the game, it just causes a dead foal.

2. Homozyogous Splash 2 (PAX3C7OY) and homozygous Splash 3 (Sps3) produce unborn game foals, where either the PAX 3 gene or the MITF gene are too broken for the foal to survive. They are also lethal in combination, that is if a foal inherits one copy of each of these. However, the Splash 1 gene, which is on the MITF gene along with Splash 3, is okay to cross with either or with itself. The 4th game Splash variation, SpsM (Macchiato) is not lethal with anything either.

3. The various combination of Kit mutations mentioned in the chart linked above. The Kit gene controls vital processes in foal development, and if the foal inherits two copies that are severely broken, the foal will not survive. There has to be at least 1 relatively complete copy of the Kit gene for a foal to survive. If both copies are too greatly broken, the foal dies in utero, and never gets born at all. This is what happened with your cross of a White 1horse with a White 2 horse--the foal inherited a severely broken Kit gene from each parent, and was never viable. The safest Kit mutations are Tobiano and Roan, which only break the Kit gene in small ways. Sabino is moderately safe. White 1 and White 2, which are each produced by one seriously broken copy of Kit are especially risky, regardless of the white factor of the two parents. There is a 25% chance of a dead foal with every such cross.

In the game, there isn't really a "paint" or a "pinto". Everything is done by genetics, so a horse can be splash, frame, or both. I actually have a splash/frame line myself, and hardly ever get a lethal foal (usually only because of the w2 that's floating through the line).

If you breed two horses who are het frame together, you have a 1/4 chance of the foal dying, a 1/4 chance of the foal not getting any Olw at all, and 1/2 chance of the foal getting frame. The easiest way to go about breeding a frame line is to have your stallions without the frame, if you want to completely avoid lethal foals.

In real life, if the horse is a Tobiano paint/pinto with no Overo horses in it's pedigree, it is likely to be safe to breed to any other paint/pinto.

It's just with the Overo paints and the paints that are some form of WhiteSpotted Kit mutation or Splash 2 or 3.

In any of those cases there is generally a 1 in 4 chance of a non-viable foal. Here's a simple punnet square base on potential results from mating a W1 mare with a W1 stallion. It makes it easy to see the genetics working out.

http://www.pbase.com/malewis/image/162880040/medium.jpg