The Coefficient of Inbreeding (COI) is a number that can be a tool or a stumbling block. It can also be very confusing for first-timers. My advice is to pick livestock that fits your program goals, and not get overly focused on COI.
That being said, I do use COI in my program – as a tool and not as a marketing gimmick. Given my familiarity with my herd, it may be a tool that I use to obtain a closer related pairing (high COI) or a more distantly related pairing (low COI). With the limited foundation genetics available in Canada or even North America – most Kunekune here are going to be at least somewhat related. As of 2022, all registered Kunekune in North America came from 11 boars and 13 sows that were imported from New Zealand and the United Kingdom.
I check COI on all potential breedings I do and on pigs that I am going to purchase. The number I get doesn’t force any decision. I simply use it to determine if that individual would fit well in my program. If there are some traits I really like in an individual, I might do a tight (high COI) breeding to lock those traits in. I own a daughter and nephew from a boar I love that produces amazing (and yes, Supreme Champion) offspring. I also have a half-brother and sister with genetics I want to perpetuate in my herd. I have lots of unrelated pigs and don’t need to breed the related stock together, but I have the option if I think it will take the breed standard and my pork production forward. When breeding season is upon us, I may decide to lock in some outstanding traits of related individuals to produce a higher COI litter, or I may try to diversify and introduce a new desirable trait by outbreeding to a more distantly related individual with the trait I want that will also produce a lower COI litter. Another reason I might do a high COI litter is to weed out and cull traits I don’t like. Then I might do a low COI breeding with the offspring to diversify to see what traits unrelated genes bring me. Options! I love them.
For the sake of discussion, let’s call a COI of 1-10% on the lower end of the Kunekune genetic spectrum and a COI of 11%+ on the higher end. In a different species like dogs (with a larger pool of foundation genetics and limited cull options), what constitutes high COI may be different. For reference and perhaps an oversimplification, a first cousin pairing results in a COI of 6.25%, a half-sibling pairing results in a COI of 12.5%, a full sibling pairing results in a COI of 25%, subsequently breeding siblings from that brother and sister pairing results in a COI of 37.5%. At any point, the results of those litters can be outbred to reduce the COI.
COI math can be a bit deceptive if you don’t think it through. COI is not necessarily compounded and can change drastically between generations.
You can breed two high COI pigs and get a low COI litter. The trick is that the two parents need to be unrelated to each other. Two low COI pigs can have very high COI offspring – imagine a brother and sister from the same low COI litter – both have low COI because their parents were unrelated, but if you breed the brother and sister – BAM – you are in the double digits of COI. On the other hand, a high COI boar from a brother/sister pairing bred to a high COI sow from a different brother and sister could produce a low COI litter.
When you purchase a pig that has a low COI, it means you are purchasing a pig that had parents that were more distantly related. That may hide a few more and less desirable traits that you see at face value but it will not guarantee that the piglets it produces will be low COI. If you want to breed for low COI or high COI piglets, you really have to enter both parents into a COI calculator to see what you will get. In the example here, you can see the sire (Robert Bakewell) has a higher COI of 13.28% and produced offspring with a COI of 6.46%. Note: the IKHR vs. AKKPS tools may calculate different results.
A close genetic pairing (high COI) concentrates genetics. It will accentuate bad and good genetics. So some hogs will win the genetic lottery and get the best of their ancestors, some will get a bit of both, and some may be the worst of their genetics (maybe or maybe not trainwrecks – but at least we can say they would likely not an improvement to the breed). That is where a pork and cull program is important if you want to dabble in the taboo arts of high COI pairings. This is why raising some pigs for pork is an advantage – the best can be kept as breeders and the rest can be raised as pork. Some might say, “breed the best and pork the rest.”
I probably wouldn’t recommend that a beginner starts with two highly related pigs as it takes some time to get an eye for what you want and what you don’t want. If you pushed me for a number, I might say start with a pair that produces a litter of a 10% COI or lower.
There are online tools through the membership portal at IKHR (Inbreeding Analysis) and AKKPS (Trial Breeding). Be warned – you can enter the exact same parents into both COI generators and get completely different results. I stick to the IKHR tool as they have a bigger database and it is my primary registry. The two COI calculations below are for the same pairing, one yields 4.27% and the other 7.5%. That is a big difference for the exact same litter of piglets.
So I’ve postulated some ideas here that go against the mainstream marketing campaign of low COI pig mills. In those cases, I can see how it makes sense to always keep COI low if most or all animals in that population go on to reproduce and are not carefully removed from the breeding population through harvest or castration. Don’t get me wrong, I like low COI for lots of reasons, but not to hide genetic deficiencies. I want to improve the breed and weed out traits that negatively impact health and soundness – I just think that can sometimes be done with low COI pairings, and sometimes with high COI pairings.
My undergraduate degree was a Bachelor of Science specializing in Biology, so the importance of diversity in populations does not elude me, but that same student in me always wants to dig a bit deeper. Can you have a diverse population and high COI individuals? Yes. Can those high COI individuals be outbred to share and diversity their genetics? Yes.
Can those high COI individuals represent the best of the breed? Yes! Let me show you. There are some AMAZING pigs in the herd book that have very high COIs. At the time of writing, the IKHR Herdbook contained 14 “Supreme Champion” pigs that were judged to be the best of the best. Included are famous foundation pigs like Robert Bakewell and Hamish. For fun, I calculated all their COIs.
Now a few earlier hogs do not have enough ancestors in the database to have meaningful COIs (they are recorded as 0%), so I am just listing the data there is. From top to bottom the list of IKHR Supreme Champions has COIs of: 21.48%, 13.28%, 13.28%, 31.25%, 16.91%, 12.5%, 6.55%, 5.91%, 11.8%, 3.57%, 7.7%, 26.96%. With the threshold of a 10% COI, I would say 4 Supreme Champions have low COIs and 8 have high COIs – some are not just double digits, they are just about as high as they get – 20 to 30%.
I will hypothesize that market preference and increased availability of different bloodlines have lowered the COIs of Supreme Champions over the years in the competitions, but as you can see from the 2021 Winter Supreme Champion, Sassie, it is still being done with success. What I am saying is that a high COI doesn’t mean you won’t get a great pig, in fact, the majority of the best shown Kunekune in North America at IKHR sanctioned shows to date have high COIs. So it is safe to say some of the BEST pigs have a high COI. It is, however, important to qualify that there are also probably a lot of trainwrecks out there with high COIs, so go thinking I am touting it as a miracle number. It is just a tool. It would be fair, from an understanding of genetics to say some of the WORST pigs probably also have a high COI. I am sure these high COI pairings exposed weaknesses that should/could/would have been culled (think Bacon) to remove those weaknesses from the population. A low COI becomes more and more important to me if I were to buy a pig that doesn’t represent the best of its parents or from a breeder selling every single piglet as breeding stock. In those lottery cases, I’d lean towards a low COI pig that had more genetic forgiveness rather than gamble if I would be given a genetically superior or deficit piglet. That would all change if I trusted the breeder to select and cull.
Now after all that brain dump on “what I think about COI”, I still mostly produce a lot of diverse, low COI breedings and really only dabble with the occasional high COI breeding when something excites me. I am often more of a spectator than a participant. It just hackles me up when low COI is touted without rationale or context.
If you are genuinely interested in using high COI pairings like many old-line swine breeders use to improve their breeds, check out Corva Bella Farm. Cristiana has written extensively (here’s a sample) on her work closely breeding a related population of Kunekune. She even produced the Winter 2021 Supreme Champion (Sassie) that was a result of a Brother/Sister pairing. Then go to some old-line swine groups and see what has been done in other heritage breeds.
At the end of the day, if you see a scary 13% COI piglet or are thinking about doing a 13% pairing, don’t just pick a lower 6% COI piglet or pairing JUST because of the number. There are lots of reasons to consider. If all things were equal between two piglets, yes I might pick the lower COI one, but decisions are never that simple. Pick the piglet/pairing that best fits your farm goals! Remember, there are plenty of Supreme Champions representing the best of the breed that have a high COI. They existed because their breeders did a related pairing that resulted in high COI litter. Aren’t we all glad they didn’t look at the potential high COI and decide not to do it? For me, the key to high COI breeding is knowing the genetic benefits and risks, and having a strong pork program to cull results that do not represent the best of their parents’ genes.