There is an old joke among farmers. The newbie farmer asks the grizzled veteran farmer: “What is the difference between line breeding and inbreeding?”. To which the grizzled veteran farmer replies “Line breeding is when I do it. Inbreeding is when you do it.”
In all animal husbandry (including the breeding of livestock) one of the resources sometimes available to breeders is a value called the Coefficient of Inbreeding (COI) . In my experience it is a misunderstood value that is often counter intuitive to many breeders(including myself). I could take an entire post explaining the concept of COI in depth. But for the purpose of this discussion I will summarize it as follows:
- There are several methods of calculating COI. Each results is a slightly different numerical value. However in every case it is a statistical prediction of what can be expected to the level of inbreeding(explained below) is in a group of pigs with identical sires and damns. It is not the ACTUAL level of similar gene pairs in any one animal.
- COI as a percentage is calculated based on the number of common ancestors the sire and damn of any offspring share. The resulting analysis of these common ancestors predicts the occurrence of identical (homozygous) gene pairs where dissimilar (heterozygous) gene pairs would be expected. So a pig with a 25% COI would be expected to have 25% more homozygous (similar) gene pairs than the offspring of two completely unrelated pigs.
But the real question is not how COI is calculated but is it a goal or a tool? There is no term I know of that carries a more negative connotation than “inbred”. So is a low COI pig better than a high COI pig? If that answer is yes then low COI is a goal. Or is knowing the COI of a potential breeding a clue to how to improve the consistent expression of positive traits in any purebred animal? If the answer to that is yes then COI is simply a tool. And finally ,and most importantly,can the overall COI of a limited gene pool herd of critically endangered animals such as Meishans be managed long term? All while improving the breed and increasing its numbers.
Lets look at the following 2 examples:
Example A: The sire of a potential breeding has been the result of 4 generations of brother sister breedings. The damn of this potential breeding has been the result of 4 generations of brother sister breedings. Both pigs reflect the symptoms of inbreeding depression.Both are poor examples of the breed.Both have extremely high COI values. Intuitively many would expect two high COI pigs to produce high COI offspring. But if both the sire and the damn come from unrelated breeding branches the resulting piglets will have a 0% COI.
Example B : A sow exhibits an unusually high percentage of desirable traits (ie litter sizes,loin length,growth rate etc). In an effort to lock those traits into future generations one of her boar piglets by one sire is bred to one of her gilt piglets by another (unrelated to the first sire) . The result of that breeding would give you piglets with a 12.5% COI.
Which is better? The 0% COI litter from inbred parents or the 12.5% COI litter from the more closely related breeding? The answer? The answer is you wont know until you look at the results of the breedings.
Breeding is like spinning a number of different genetic roulette wheels all at once.Because like the roulette wheel all animals have many traits they carry (genotype) and fewer traits they show or express (phenotype). When you have a 0% COI you have more values on the DNA “roulette wheel”. You will typically get more range of traits and less consistency with repetitive low COI breedings. Breeding more related animals results in fewer traits on the genetic roulette wheel and a higher probability of expressing or locking traits in offspring. That can mean locking positive traits into future generations but that can also mean expressing normally recessive negative traits . So COI is truly a tool to be used by an informed breeder and not just a numerical score that defines “better” in a one dimensional way.
The American Meishan Breeders Association feels each breeder should have the most information possible going forward in making future breeding decisions.The A.M.B.A. will not direct breeders or restrict breeder decisions on COI in any way. What we will do is provide accurate pedigree information through our on line pedigree system. In addition our members now have access to our on line inbreeding analysis tool.With this tool you can look at the predicted COIs of not only pairings of any two registered Meishans but you can even look at the predicted COI’s of the offspring of up to two unique pairings of registered Meishans. This is another way we are constantly striving to deliver value to our membership and to provide the tools needed to track the COI of individual litters. As well as make informed decisions on potential future breedings . This tool also allows you to see how bringing new registered Meishans into your herd might impact your overall COI levels of future breedings.
Moving forward is the overall COI of the registered Meishan herd “manageable”? The answer is also yes. If our member breeders properly manage and maintain the three unique recognized bloodlines of the North American Meishan herd. Then our members can judiciously cross those lines so there is sufficient genetic diversity already present to allow for long term growth of the breed .All while maintaining the genetic health of the breed. The A.M.B.A. will continue to develop tools like our online inbreeding analysis tool while working to track the overall COI of the populations of piglets our members produce on an annual basis.
So what is the real answer to” what is the difference between line breeding and inbreeding.”
Our response is
” Line breeding is the conscious act of an informed group of breeders ,carefully weighing the risks of more closely related breedings , in order to improve successive generations of a breed. Inbreeding is the result of uninformed breeding decisions, no matter how well intentioned, that express ,and potentially lock,the recessive negative traits of any breed”.
I hope that helps. Be well and thank you for your support of the fight to save the Meishan Breed in North America.
American Meishan Breeders Association