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Do you mean that the foal would have gotten Extensive White Factor and that means that the gestation went wrong? I thought it should pick up after its parents: Medium or Large? Or is it more random?

Or do you mean Kit Promoter? For example this horse has
W10/M and KP/KP and White Factor Large and survived: https://mesa.horsegeneticsgame.com/horse.php?horseid=3667136. My foal should've only had one copy of KP.

I updated the message so it now tells you the specific KIT combination that was lethal.

Hi! Going to offer some answers here, as I own a lethal white carrier in real life (Frame half Arab mare) and have looked into genetics heavily. Anyone is free to correct me if I am wrong anywhere!

1. Avoid this combo when both horses have a high white factor. W10 alone is enough for me to say no more KIT patterns: my W10 horses
If you look, AltaMax also carries W20 and KP in addition to W10 so I will be very careful with his matches.

2. See this forum post on how white factor is going to work soon. Ammit will have to answer to how it works exactly now.

3. If you have a high white factor, you have a high risk of lethality. Think about it this way: in real life, KIT mutations can affect actual working body systems of the horse, as they are also tied to body functions. So the more white you have, the more likely that the horses systems are affected too. You CAN have healthy max white foals. I own several on here: Denver City Cat who has a minimal white factor with KP2 (he has 4 max white foals and many near max white foals), Lost Diamonds who has an extensive white factor with tobiano and W2 (an example of a safe mix of white patterns, not only KIT), and recently sold Style Loves who has a double KIT pattern, minimal white factor and is KP/KP2.

4. I have found that KIT Promoter does heighten the risk of lethality when mixed with high White Factor. I like KIT Promoter to boost the minimal white factor horses, but I don't want it on my higher white factor horses as I start losing foals.

I specifically breed for KIT on most of my stock. I am more than happy to help you out on questions about KIT mixes until the new genetics guide is finished! See my favorite KIT mix here (W29/W20): La Bella Pricipessa & Creme Drizzle

Hi everyone, thank you for your time to put a detailed response. Sorry for my delayed reply, I noticed the update and wanted to take time to understand it better.

@lilpebbles,

2. In your example PB Denver City Cat is W29/W15 and OfMHBS Style Loves is W15/W15 and my foal was W10/M (since M/M is not lethal as far as I know).

For W15 we have this information in the genetics guide:

"Heterozygous individuals tend to have white faces and legs, and white spots on the neck underside and belly. Homozygous individuals tend to be entirely white. "

and for W29:

"White 29 - N/A skipped number. In HorseGeneticsGame.com W29 is used for horses that descend from the 1 millionth horse created in the game."

It doesn't say anywhere that W29 can be letal, but it's probably not since it's a made-up gene and W15 is non-lethal even when homozygous. So I assume that any W15 and W29 combos are safe by the extension.

3. From your examples and me playing with the search it appears that KP and KP2 doesn't have any influence on White factor. If it doesn't influence WF then it probably doesn't influence lethality, since it's the white that causes deaths? I don't know if that's correct, but I don't see the correlation. The horse can be KP2/KP2 and have None WF:

https://mesa.horsegeneticsgame.com/adv_search.php?runsearch=go&jump=0&50=2&51=2&56=0&57=0&58=0&59=0&60=0&61=0&110=1&179=2&180=2&181=2

I specifically breed for KIT on most of my stock. I am more than happy to help you out on questions about KIT mixes until the new genetics guide is finished! See my favorite KIT mix here (W29/W20): La Bella Pricipessa & Creme Drizzle

These are beautiful, especially Bella!

I really like bold patterns in horses and try to avoid all white horses. My favorite KITmutations are M, PW, but I'm also interested in W10 and W8, that's why I'm interested in breeding W10/M to M/M which I thought is safe, especially considering that the dam was already W10/M (was trying to replicate her look).



@Ammit,

Thank you, looking forward to the updated guide!

In the meantime if you are finding the chance of foals dyeing very distressing I would just avoid potential W10 to other KIT crosses.

The issue is that I don't understand what is the chance even approximately. Unfortunately there's no information in the guide and I don't have the access to the source code to read it. It would make a big difference in decision making to know whether potential lethality is 1% or 85%.

For example guide says:

Mutations that produce all white individuals with only a single copy are definitely going to be lethal with other high white KIT mutations and might also be lethal with roan, or even tobiano.

Neither of the horses I bred were fully white or mostly white, I would estimate that the mare had maybe at most 50% of white areas on her hide (looking at the pixel horse :D ) .

After the update my dam now has HPS5 White Factor: WF1/WF2 KIT: W10/M, and the sire now has KIT: M/M and WF2/WF2. Do I understand it correctly that this combo shouldn't be lethal anymore given that the white factor of a foal should be either Medium WF1/WF2 or Large WF2/WF2 guaranteed now that it's inheritable?

I see that some of the other horses that had W10/M and Large WF were mapped as WF1/WF3. Would this be a safe combo too? Does the larger number has (WF3 > WF2) has any impact at all or is total sum more important? WF1 + WF3 == WF2 + WF2?

FireElement you are asking for a level of specificity and exactness that I can not possibly give you right now. Those answers don't exist yet. HPS5 White Factor isn't even fully implemented yet. I understand it is stressing you out a ton that you have some foals dying. The only advice I can give you right now is to avoid crosses that have produced lethal foals for you, if you find that upsetting. I can't give you percentage chances because that varies wildly by the parents.

As I said above " I won't be able to put that update in until we finish some updates to WF and KIT." I promise I will add this information to the guide, when it is possible to do so. With KIT though there is always going to be some randomness.

I apologize for that being an unsatisfying answer, it's the best I can give right now. I am working on a simplified model of lethality, but I don't know what form that will take yet.

As for KP it has a mild boosting effect on lethality. As does splash and frame.