09/13/2026
A good read!
Inbreeding vs Linebreed Educational Post
I see a LOT of misinformation about this topic. So let’s clear some things up.
Linebreeding IS inbreeding. The only universal definition to “linebreeding” is breeding relatives with the intent of capturing the good traits of a shared ancestor. Depending on what species you’re in, sometimes what breed, and even the individual you talk to, linebreeding can be extremely close inbreeding or fairly distant inbreeding. But it is ALWAYS inbreeding.
ARBA’s Guidebook used to have a version of Felch’s chart for line-breeding (pictured), which is where a lot of ideas for what is and isn’t linebreeding and what is and isn’t safe came from. Really, it was from a misinterpreting of Felch’s chart that these incorrect ideas came about. Felch’s chart was meant to be a way to track the exact genetic relationship between linebred animals. Specifically it was designed by a poultry expert for managing poultry flocks, but it works for other species as well. It’s meant to be used with a very high quality founding pair that’s completely unrelated and preserve the best traits of the founding stock, locking in those best traits, while maintaining enough genetic diversity to have a lower risk of health issues. It’s a very useful tool when used as intended, but it’s been very misinterpreted. It’s also not the ONLY way to lock in good traits while maintaining similar or even equal levels of genetic diversity.
We tend to be very scared of the word “inbreeding”, but it’s not necessarily a bad thing in and of itself. Controlled, careful inbreeding is how you set In good traits. It’s how you develop constancy in your stock. It’s how top winning rabbitries continue to produce that extremely high caliber of quality year after year.
Of course, if it’s not carefully controlled, things can go wrong. If it gets too close, things can go wrong. If you’re inbreeding rabbits without knowing how to run an efficient linebreeding program, things can go wrong.
Sometimes, even with all the best knowledge and calculations, things can go wrong. HOWEVER, things can and also do go wrong when breeding completely unrelated animals. That’s just a risk of breeding any two animals. Period.
So, what is too close? Well, that depends on a lot of factors! What species are we talking about? Some species handle inbreeding a lot better than others. Humans handle inbreeding terribly, which is one of the reasons the word scares us so much! Species that handle inbreeding well generally do so because the deleterious (harmful) alleles (gene variants) have already been purged from the population. We can artificially do this with careful inbreeding to bring deleterious alleles to the surface and eliminate them, locking in only the best alleles.
What is too close also depends on how related the animals further back in a pedigree are. Breeding siblings from two completely unrelated parents is safer than breeding siblings from parents who were already related. The biggest problem is that we often lack ancestor information for further back than 3 generations in some species (such as in rabbits and chickens). Ideally, you want to know all the ancestors as far back as possible, and at least 8-10 generations back. This information just often isn’t available in many species, so people tend to play it safer because there’s the implied idea that within any given breed, it’s likely there is relatedness further back in the pedigree. In a closed registry (no outside animals are allowed to be bred in after the closing of the studbooks), every animal in a breed is already some level of related. It makes sense to be more conservative and cautious about any type of inbreeding in such a registry than in one that has an open registry (outside animals allowed in). Once a studbook closes, no new DNA is coming in. Every generation tends to further and further lose genetic diversity.
Rabbits are an open studbook species (at least through ARBA). Most breeds have had outside breeds crossed in at various times. This means it’s inherently safer to more closely inbreed most breeds of rabbits than it is some species such as dogs (which generally have a fully or partially closed studbook). The chances of two rabbits being more related further back than we know is less. Which means outcrossing is more likely to be actually an outcross. That said, within any given breed, there are still likely to be relatedness between different individuals, even if it’s not on the pedigree. We do have to keep that in mind.
Now, another common misunderstanding is that it’s safe to breed parent x offspring but not sibling x sibling. Parent and offspring have a coefficient of relatedness (R) of 0.5. Parents share 50% of their DNA with their offspring. Siblings also have an R= 0.5. Assuming siblings aren’t identical twins, siblings share 50%* of their DNA with each other. It’s the exact same level of risk to breed parent x offspring as it is to breed sibling x sibling.
Let’s talk about coefficient of inbreeding (COI). COI tells us the probability that an allele was inherited twice from a common ancestor. This matters when we are talking about harmful alleles (versions of genres) that are recessive. Recessive means you need two copies of the same allele for the trait to show up. Chocolate color is an example of a recessive allele. You need two copies of the chocolate allele (b) to make a chocolate based color. Just one copy (Bb) makes a normal black based color. All fine and well when it’s just a non-harmful color change, but when it’s something that relates to the health, we really want to try to avoid doubling up on those recessives. With higher COI, the risk that we doubled up on a harmful recessive increases. So, of course we generally want to be careful with that.
However, once again, the COI of a rabbit from a parent x offspring breeding is the exact same as the COI of a rabbit from a brother x sister breeding. Either way, the rabbit has the exact same risk of having inherited a harmful allele from the same ancestor.
Again, this risk can be controlled by purging the line of harmful recessive alleles. The only way to do that is by heavily inbreeding.
So far, it may seem that I’m in favor of inbreeding as much as you like. Heavily inbreed and select out any that show harmful alleles.
Except there’s one more thing to consider! There are a few things that aren’t inherently harmful or good. Some genes it matters less which particular version you get and matters more that you get different versions from each parent. Adaptive immunity is a form of immune system that evidence shows likely relies specifically on alleles being varied, NOT the same, to respond to a wider variety of invading pathogens. So, inbreeding of any kind can reduce adaptive immunity. (https://www.psu.edu/news/engineering/story/population-bottlenecks-cause-decline-mammals-immunity-researchers-find)
There may be other types of genes in mammals (or other animals) that also require variation to best function. Either way, just the existence of adaptive immunity means we need to be careful not to inbreed too tightly, even if we do manage to purge all the harmful alleles from a herd. If your herd (or flock, or whatever) is starting to show less resistance to disease or parasites, it may be time for an outcross. That may set you back in uniformity, show conformation, production, or other good traits, but bringing in an outside line every once in a while can maintain good immune function, which is vital!
As you may start to see, inbreeding/linebreeding is a very nuanced and often complicated subject! If you don’t know your line well, outcrossing is generally safer. If you don’t understand how to do controlled and careful linebreeding, outcrossing is often safer. HOWEVER, if you never learn these things, you’ll always be blindly throwing darts at a dartboard, hoping you hit the bullseye for that really nice offspring. Learning these things so you can do controlled linebreeding, whether distant or close, will get you far more constantly good results.
* On average. Siblings can share more or less, but it’s typically somewhere close to 50% and thus has the same COI as parent x offspring.
