If you have been a breeder of registered dogs, cats, cattle or goats, you already understand what the Coefficient of Inbreeding (CI) means and its historical and scientific basis. A simple explanation of Coefficient of Inbreeding is that it measures the amount of inbreeding present in a single animal. The higher the CI, usually expressed as a percentage, the higher the amount of inbreeding. A 25% CI is equivalent to mating half-siblings. You may get 30% or 40% or higher CI mating brother to sister depending on how inbred the parents are. A CI of 10% or less is considered to be great for a rare breed.

Why does inbreeding matter? When you mate two animals that are closely related there is a high probability that certain traits are passed on to their offspring. These traits may be beneficial, such as a large amount of functional teats, or they may be detrimental, such as a susceptibility to certain diseases or poor body conformance. Being aware of genetic diversity is critically important for any rare breed.

This is where the CI of our animals becomes useful. When making a decision of which boar to breed to which sow you can calculate the expected CI of their offspring. A simple plan would be to only mate pairs that result in lower average inbreeding for your herd.

So how do you know what will make a good breeding mate for your pigs? The answer is not simple, but calculation of the CI is a start. Also, as your customers become more educated about selective breeding they will be choosing the breeders that include CI analysis as part of their breeding management program. If you want to be their breeder of choice then make sure you breed with CI as one of the criteria.

We offer free CI calculations for members here at HHBC. But what happens if the results come back higher than you expect?

Well, what you don’t want to do is look at your poor pig and think that it’s now only good for the freezer. Inbreeding is only one factor amongst many to consider whether to breed or eat your pig.

The purpose of breeding any heritage hog is to improve the breed. We want to pass along good traits to the next generation and avoid passing bad traits. “Traits” are not numbers; they are the physical qualities and capabilities of the hog. If you are breeding for pork you should select those hogs in your herd that produce the most pork in the shortest amount of time. Large hams, roasts, long bellies; these are all good “traits” to pass on. Just because your pig is more inbred than it should be does not automatically prevent a good boar from being used for breeding.

If you are breeding to make more and better piglets you should select those hogs that do that as providers of your next litter. Sows and boars with sixteen well spaced teats, sows and boars that do their job with vigor, gilts that grow quickly and stay in good condition on lean feed; these are all good “traits” for breeding stock.

You also need to be aware of which traits are highly heritable and which are not. Number of teats, ease of farrowing, growth rates of the piglets; given similar environmental conditions these are all heritable traits. Also general body condition; straight pasterns, vertical and long legs, level backs and wide bodies can be generally relied upon to pass to the next generation. In contrast, number of piglets per litter is not very heritable and, while general “aggression” is highly heritable (think mating enthusiasm and general energy, not “meanness”), mothering ability is mostly influenced by stress, not pedigree.

So if your hog that has a relatively high CI still has great, heritable traits, don’t just ignore it as a good breeding candidate. Selective breeding can lower the CI of succeeding generations while still passing along good traits.

Now, what are bad traits that go along with high inbreeding?

Studies have shown that herds with high inbreeding don’t perform as well as herds with low inbreeding. In this case, “performance” relates to number and quality of piglets. Over time, high inbreeding lowers the number of piglets and leads to poorer quality of the piglets, such as growth rates and number of deformities that affect breeding capability.

When we have analyzed birth defects we have shown a direct correlation between them and inbreeding. Piglets that have been born sterile, have short birth canals, cleft palates, bad joints and pasterns, weak backs, crooked and crossed legs, encased penises, closed anuses and other defects are very often traced back to highly inbred or closely related sires and dams.

Linebreeding, which is a form of inbreeding, has been successfully used to screen out these defects in large herds but that requires a lot of selective culling, something that is not easily done by the small farmer with a small herd. Effective linebreeding requires the use of a large population of animals and a study of the effects of linebreeding over a long period of time. You must be able to identify heritable traits over several generations to determine whether they are fixed and beneficial or detrimental. Only then can one make a intelligent decision about what actions to take. This simply can’t be done with the small individual herds we now have in the U.S. I think it is very dangerous for new breeders to get an unrealistic idea about linebreeding their small herds. Linebreeding done improperly can result in the opposite effect than what is desired, passing along latent, damaging traits.

Linebreeding will lead to a narrowing of the genetic base of a breed and will reduce its flexibility and ability to adapt to changing circumstances in the future including ability of its immune system. These dangers have been recognized even by those who manage the largest breeds and they pose a much greater threat to rare breeds. Linebreeding can also result in loss of vigor whereas mating of unrelated bloodlines often results in greater vigor (hybrid vigor within a breed).

So what can we do, us small farmers that are breeding heritage hogs?

The first thing is to recognize the importance of inbreeding and using selective breeding with our herds. Previously those who raised these hogs bred anything to anything without regard for inbreeding mostly due to a lack of awareness and tools to calculate inbreeding. We must recognize this and work to change the manner in which we manage our herds. We must become better managers; calculating the inbreeding of each of our registered hogs and only breeding them so that the next generations have lower CIs than the current ones. We must also only choose those hogs that possess desirable traits and cull those that don’t. What this means is that, with a hog that has a high CI, we choose to mate it only with unrelated or not closely related hogs making sure that each member of the pair has those qualities that we want to see in the next generation. If we don’t have a good candidate on our farms we must seek out other farmers that have what we need and cooperate to better manage the overall herd.

So, even though your hog may be considered to have a high CI, don’t use only that criteria to determine its future. As long as it has good traits otherwise, find a good mate that together will lower the inbreeding and still pass along those traits that help improve the breed.

As for the CI number, the goal for rare breeds is to have an average CI in the larger herd of 10% or less. There is no established rule of what is too high; your goal should be to head toward that 10% average while selectively breeding those with good traits.

We have been asked whether a hog with a high CI should be registered. The answer is that any hog that is used for breeding should be registered, regardless of it’s CI, as this is the only way to track pedigrees and performance over time. Registration records are the data we and other breed associations use to determine the influence of factors such as inbreeding. Some breeders even register, or internally track, their pork herds to measure those performance factors and provide traceability for their customers and any Government requirements. Registration is a tool. Use it for your needs.