Coefficient of Inbreeding (CI) Importance

Our breeding of Large Black pigs has one goal ~ Develop the most genetically diverse purebred animals possible to ensure the viability of the breed for future farmers. Our children have asked if they will get to raise this breed when they grow up. We believe it is possible but only if more farmers choose to become breeders. Bearing that title comes with the responsibility of breeding for the future of the breed and not just for a dollar today. To better understand our breeding efforts at Lucky George Farm we have put together a list of Frequently Asked Questions:

What is inbreeding?

Inbreeding is the mating of related individuals, i.e. individuals that have one or more ancestors in common.

What is close inbreeding?

Close inbreeding is the mating of close relatives. The closest form of inbreeding in domestic animals involves matings between full brothers and sisters (full sibs) and between parents and offspring (collectively called first-degree relatives). The next most close form of inbreeding involves matings between grand-parents and grand-offspring, between half brothers and sisters (half sibs), between uncles/aunts and nephews/nieces, and between double-first cousins (collectively called second-degree relatives).

What is linebreeding?

Linebreeding is a term commonly used to describe milder forms of inbreeding. Typically it involves arranging matings so that one or more ancestors occur more than once in a pedigree, while avoiding close inbreeding. Because many breeders apply the term “inbreeding” only to close inbreeding, we will refer to inbreeding/linebreeding in answering other questions.

What is the effect of inbreeding/linebreeding?

On average, the effect of inbreeding/linebreeding is an increase in the prevalence of inherited disorders, a decrease in viability and reproductive ability, and the loss of genetic diversity (i.e. decrease in genetic variation). Collectively, these effects of inbreeding/linebreeding are called inbreeding depression.

How is inbreeding/linebreeding measured?

The Coefficient of Inbreeding (CI) measures the extent to which an animal is inbred/linebred, compared with animals in a reference population that are assumed to be unrelated and have zero inbreeding. Typically the reference population is the earliest generation of animals for which pedigree information is available. The CI ranges from 0% (equivalent to the reference population) to 100% (completely inbred). It is important to note that the CI is NOT an absolute measure. Instead, it is a relative measure, i.e. relative to animals in the earliest generation of a pedigree. However, at the top end of the CI scale, being 100% inbred has an absolute meaning: the animal is completely inbred.

How many generations of pedigree are required to calculate the coefficient of inbreeding (CI) of an animal?

CIs can be calculated from two or more generations of pedigree information: CIs calculated from two or three generations show the extent of recent inbreeding; CIs calculated from a larger number of generations include longer-term inbreeding as well as recent inbreeding, and hence tend to be larger. The main thing to note is that in order to compare CIs, they must be calculated from the same number of generations of pedigree information.

What would be an acceptable/good CI range to strive for?

There is no acceptable level of CI below which there is no risk. The harmful effects of inbreeding increase in magnitude as the CI increases from 0%. Because of this biological reality, breeders should be aiming to arrange matings so as to minimize the CI of offspring. In other words, breeders should be aiming to arrange matings between animals that are least related.

How will I know if I am experiencing inbreeding depression with my Large Black herd?

This depends on how inbred your pigs are and how many generations the level of inbreeding has been occurring for. We’ve listed some of the issues brought on by inbreeding in order of impact to the future of the breed. The more inbred your stock is the more of these you will see and in greater severity.

  • Fewer piglets in a pregnancy
  • Chromosomal defects in live pigs (Dwarfism, hermaphrodites, scrotal hernia, cryptorchidism/undescended testicles, nipple abnormalities)
  • Deformities in live pigs (missing limbs, missing eyes, cleft pallet, blind anus)
  • Stillborns
  • Deformities in stillborns (mummified pigs, fetuses that stops developing)
  • Sows aborting litters before term
  • Trouble getting a sow pregnant
  • Sows/Boars being infertile

I know of a pig/s with a relatively high CI and it is perfectly normal. How can this observation be consistent with inbreeding being harmful?

Animals with high CI that appear to be healthy do arise from time to time. From the creation of inbred lines in laboratory animals, we know that it is possible to create such animals with a CI of 100%. However, the evidence from the creation of these lines shows very clearly that the chance of creating such an animal is extremely low; and that in order to create such an animal, many thousands of animals will be born with serious health and reproductive problems.

If you are interested in the genetic science behind inbreeding and its effects you can read the paper by clicking on the link. It is a demonstration case of the creation of an inbred line of mice, only one of 20 lines survived; the rest went to extinction due to inbreeding depression Bowman and Falconer [1960] Genetical Research 1, 262-74. Furthermore, detailed examination of completely inbred animals often reveals abnormalities that are not evident to the naked eye.

What does responsible breeding look like?

We believe it begins with purebred breeding stock that looks genetically diverse on paper and in body. Begin by breeding pigs that are conformationally sound OR as close to conformation excellence as possible. Secondly, and just as critical, is the level of inbreeding within the individual animal’s pedigree. We look for diverse genetics within their lineage and a low (under 15%) coefficient of inbreeding (CI). Our desire is to breed purebred boars and sows together that will result in piglets under 15% CI in 2016. By executing our breeding strategy we know we will be producing purebred pedigree Large Blacks with CIs under 10% within 2 years and under 7% within 3 years. That means every piglet produced on the farm whether for pork production or as a potential breeder will have lower CIs.

We feel that intentional breeding with pedigreed purebred stock is key to conserving a rare breed like the Large Blacks pig. In order to see the lineage and genetic makeup of a pig it is necessary that the records are true and clear for all potential owners to see. Knowing the history of an individual animal allows an owner the opportunity to decide whether they may want to breed their pigs. If they do breed, whether or not the resulting litter has the “hidden” genetic traits to strengthen the breed or weaken it by passing on undesirable traits. Every pig owner is not a breeder, every pig is not breeder quality, and one pig with bad genetic traits can reproduce a lot of genetically defective pigs.

We do not need to breed as many pigs as possible to conserve a rare breed. That action in the end is extremely detrimental to a rare breed. It is the selection process used to breed only the best purebred pigs to the best purebred pigs. Hopefully after reading the above information you can now see that “Best” at Lucky George Farm begins with purebred Large Black pigs that have pedigrees tracing back to Great Britain, low CIs, excellent conformation, as well as culling pigs out of our breeding program and moving them into pork production. We are picky and demand the best genetics because we want our children to have the opportunity to raise purebred Large Blacks 20 years from now.


Only pigs good enough for our breeding program will ever be sold as a breeder off of our farm.

Cull hard and cull often because UGLY PIGS TASTE GREAT!



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