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I've been doing some research on breeding rabbits and saw many people mentioning that if you inbreed rabbits (father-daughter/mother-son/sister-brother) that there is only a small chance of birth defects and a chance at an improved outcome if the stock is already good.

There is another party that says inbreeding leads to serious side effects including fused spine, skeletal problems and missing or extra limbs example this video.

What does the science say? I would be interested to find a range of answers if there is a difference between "first generation" of inbreeding and if it makes a difference if recurring inbreeding happens?

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  • You mean for rabbits or in general, e.g. also for humans? It might be quite dependent on the species, e.g. number of chromosomes and gens etc. Anyway, I'm pretty sure that it gets worth if you keep inbreeding, because the number of identical gens (which can have defects) is increasing.
    – Martin Scharrer
    Apr 14, 2012 at 11:58
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    One of the big concerns with inbreeding is that recessive defects that are extremely rare in the population and therefore (being recessive) are almost never expressed, could quite easily end up on both your loci if both the paternal and the maternal DNA are from the same original strain. Being diploid mammals, I don't see that rabbits could be excepted from this rule.
    – David Hedlund
    Apr 14, 2012 at 12:30
  • In Australia, an incestuous family spanning several generations has been found. Many of the kids suffered from serious defects such as misaligned eyes, walking impairments, etc.
    – Twilight Sparkle
    Feb 25, 2014 at 13:05

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In general terms, inbreeding is dangerous because it increases the chances of homozygosity. This means that for a particular gene, identical alleles of the gene are present on both homologous chromosomes. Those individuals result of the inbreeding have more chances of having recessive or deleterious traits.

These are generally 'invisible', they don't express physically, but they are present in the genes so if a person has two of them, they can become a manifest trait. Some examples of negative traits are reduced fertility, increased genetic disorders, lower birth rate, higher infant mortality or loss of immune system function.

You can calculate the risk of recessive traits (an example of inbreeding calculation for dogs, and more info here). It is greater when the parents are close relatives and lower for relationships between more distant relatives:

A measure of inbreeding of an individual A is the probability F(A) that both alleles in one locus are derived from the same gene in an ancestor. This probability F(A) is called the "coefficient of inbreeding".

Both the inbreeding and the coancestry coefficients can be defined for specific individuals or as average population values, but they assume no selection or are limited to neutral alleles, so the numbers are a simple statistical calculation.

If you want to know how inbred a population is, you can use the effective population size. You can note how the average inbreeding coefficient changes from one generation to the next, and then define Ne as the size of the idealized population that has the same change in average inbreeding coefficient as the population under consideration.

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