¶ Inbreeding
This is a topic that gets brought up a lot in horse breeding games, so let's discuss it a bit.
In case you don't know, inbreeding is the mating of closely related horses. We'll start off by letting you know, yes, you may inbreed horses in Legacy, but no, it is not a ‘bad’ thing, and you will not be penalized. (*this may not be entirely true. You'll want to read on to learn about the risks of inbreeding)
¶ What is the purpose of inbreeding?
Let's start off by just thinking about the purpose of breeding any horses at all, inbred or not. Why breed them? Well, simply put, we breed horses in order to produce another generation better suited to whatever our uses/needs/goals are.
On the genetics side of this, that means there are alleles that benefit our goals, some that have no effect on what we're interested in, and some that have negative effects. With breeding, your goal is to produce horses who have more of those good alleles, and less of the bad. So, essentially, you are trying to reduce genetic diversity in your herd to get only the genotypes that help your goals.
Inbreeding is a relatively quick way to reduce genetic diversity. How is it quick? Let's think about things on a gene level. If you look at one horse, that horse only has a set number of alleles they can pass on to their offspring, but, if you have a herd of 10 horses, all of those horses combined will have more unique alleles than just any one horse. If you never inbreed with those 10 horses, you have a lot more alleles to deal with. If you pick 1 horse and inbreed to them, there are less alleles. Less alleles means you have less genetic diversity.
¶ But wait, I thought inbreeding was bad? You make it sound good!
I never said it was either. I simply described what it does, i.e. reduces genetic diversity.
Reducing genetic diversity can be good, if you only end up with good alleles. Horses in Legacy have over 600 genes, not to mention <5% are testable, which makes it extremely unlikely that any one horse only has good alleles. Additionally, for some genes, the heterozygous animal may actually perform better than either homozygous option, so reducing diversity at that gene is ‘bad’ no matter what (this is known as heterosis, or hybrid vigor).
¶ Why does inbreeding get such a bad rap though?
This is because inbreeding increases homozygosity, which can unmask bad recessive alleles you didn't know were in your herd.
Let’s walk through an example.
Say you have a stallion (the half yellow half green horse at the top of the pedigree below) you breed to two unrelated mares (the two green horses to the left and right of the stallion). The foals end up being male and female, and they are the best horses you have. Because of this, you decide to breed them together to try and get an even better horse. But, little did you know their sire carries a bad recessive allele that is ‘hidden’ by his good allele (represented by the yellow color). Unlucky for you, both his colt and filly happened to inherit the bad allele, and they both are heterozygous. Now, if you breed them together, you have a 25% chance that you will get a homozygous foal, and the allele’s bad effect will no longer be hidden (the yellow grand foal in the pedigree).
¶ So, you must be careful with inbreeding
If the horse you inbreed to has a lot of bad alleles, it will become very likely that the inbred offspring will be worse. But, if you are very careful about horses you inbreed to, you might get really good offspring.
I should clarify really quickly too though that homozygosity of bad alleles can happen even without inbreeding, so this problem is not unique to inbreeding. Inbreeding is just more likely to reveal them.
¶ What about diseases though? Doesn't inbreeding cause diseases?
It can certainly reveal recessive diseases. Just like the example above, if your horse carries a recessive disease allele, inbreeding to them might reveal it. But, if the horse you inbreed to does not carry a recessive disease allele, then you won't get disease by inbreeding.
¶ What about in the game though?
There is no blanket penalty for inbreeding in the game, like some 50% reduction in an inbred horse's show scores or something like that. That's not realistic. The only potential penalties are just the risk of getting horses with homozygous bad alleles, just like in real life. There are a few big ones to watch out for:
¶ Untestable, recessive, ‘inbreeding’ diseases in Legacy
There are 4 untestable, recessive diseases in Legacy. They are rare though, so it is highly unlikely you will encounter them without inbreeding your horses.
¶ Equine Hypohidrosis/Anhidrosis
This disease causes a horse to either not sweat, or sweat very little, which makes them overheat during training. As a result, they won't be able to do as many sessions as other horses.
¶ Equine Metabolic Syndrome
Horses with this disease put on weight abnormally easy. They will gain weight even on basic feed, so they are prone to becoming fat and developing Metabolic Laminitis. You will need to be careful to manage their feed and exercise.
¶ Equine Asthma/Heaves
These horses lungs don't work quite right, and they will breath heavily during training or exercise. But, there is a medication to help them, you will just need to pay a monthly fee for the prescription.
¶ Keratoma
A keratoma is a tumor that develops in the hoof wall and causes lameness. They will develop when the horse is between 5 to 8 years old, and will require a one-time surgery to remove (it's not cheap either!).
¶ Inbreeding's effects on Fertility in Legacy
Inbreeding, especially very heavy inbreeding, is very likely to decrease a horse's fertility, just like in real life. Horses will never become completely infertile in Legacy, but just be aware it can get pretty bad!
¶ What about COI? Why don't we show that in the game?
We don't show this statistic because it is often misunderstood and misused in games.
What is it? COI stands for ‘Coefficient of inbreeding’. Its a percentage that tells you about how inbred an individual is, with 0 being not inbred at all.
But, have you ever stopped to think about what a percentage tells you about inbreeding? If a horse has 10% COI, what does that 10% actually mean? Is 10% of their genome from one ancestor? Is 10% of their pedigree made up of one ancestor?
The answer is neither. It doesn't even tell you anything about one ancestor.
What it tells you is, if that individual with 10% COI has some homozygous genes, then there is a 10% chance that both the alleles at that locus are ‘identical by descent’. That is, they came from the same ancestor. They can be homozygous for a gene but the alleles are not identical by descent though. They can be inbred to multiple ancestors too, and COI is still one number that just tells you an overall probability, and not just for one ancestor.
Confused? This is why we don't use it in the game. You don't need to worry about it at all, this was just extra information about statistics.