Editor’s Den—Volume 1, Number 2, February 2004

Understanding the Full Implications of Using Relationship Co-efficients (RCs) in a Selective Breeding Program

By Marlette Love-Goodnight

There are many tools breeders can use to manage their breeding programs and that buyers can use to research litters. So understanding these tools becomes important for both those producing puppies and those in the market to buy puppies.

One such tool is called the Relationship Co-efficient (RC). Let us start off by defining it. In essence, an RC is a measure of pedigree relationship or the “correlation between the breeding values of two individuals due to pedigree relationship alone¹.” Basic RC calculations are pretty easy to “compute.” Using Puppy X, the following gives the RC percentages for three generations plus siblings:

But it starts to get complicated after this. When one hears “RC%,” one needs to know exactly what the speaker is referring to in order to make sense of the information. For example, a breeder could give you the RC percentage of a potential pairing which might mean the RC you are looking at is the estimated shared ancestry of the parents. It will not tell you what the “inheritance factor” is because you already know a puppy gets 50% of his/her gene segments from the sire and 50% from the dam. But if there is a dog with a trait or fault that is back in the pedigree, you could do an RC between a dog you want to breed to or a potential puppy and that specific ancestor and calculate the probability of “inheritance by descent.” You can (or rather a computer program can) also do an “overall” RC based on the combined individual RCs in a pedigree².

As you can see, the formulas for computing RCs are complicated and there are computer programs designed to make it much easier providing there is accurate pedigree data. However, it has been my experience that not all pedigree computer programs compute the same RC percentages depending on how they are programmed (or depending on the accuracy of the data). But what we really have to ask ourselves is what does the RC percentage really tells us, and how can we (breeders and buyers) apply that knowledge to our individual endeavors.

Based on the definitions above we can deduce that it helps a breeder determine the probable percentage of genes coming from a specified ancestor. For example, I’m going to pretend I have a 10-generation pedigree on Ash (which I don’t so all these numbers, percentages, and names in this example are fictitious). I might see a dog called Studly appear 12 times in Ash’s pedigree. I could run my pedigree software (if I had any) and compute that when evaluating Ash’s pedigree and Studly, his RC is calculated at 17.63 percent. That means that Ash has a 17.63 percent chance of inheriting one or more genetic traits from Studly.

As a breeder, if Studly has great genes (good genetic traits) there is a slim chance Ash will inherit genes from Studly. However, if Studly has bad genes (one or more bad genetic traits), there is also a good chance Ash will not inherit those genes providing the trait is not polygenetic, which puts an entirely different spin on it. As a buyer, this sounds pretty impressive if Studly has some bad genes because there is a less than 20 percent chance Ash will inherit Studly’s bad genes.

But right now the RC is nothing more than a probable number of inheritance—it does not tell me anything about “what” could be inherited and it does not tell me about the inheritance factor of the sire or dam which we know is higher than 20 percent (more like 50 percent).

So, what does that mean? It means that the pedigree is a probability roadmap and its usefulness (and RC and Inbreeding Co-efficient (IC) percentages derived from it) depends entirely on how much you know about the lines (dogs) themselves. The sire and dam can be affected with a genetic disorder (could be the same, could be different, could be more than one disorder) and the RC or IC percentages could be very low and it still will not give you healthy puppies! In the same vein, if the line is healthy and stable, you stand a good chance of getting a healthy, stable puppy even if the RC and IC percentages are fairly high.

It is very easy to get “snowed” or intimidated by numbers. It looks good to throw these RC and IC percentages around—makes it look like a breeder has an impressive breeding program. And some breeders know what these numbers mean and use them appropriately—some do not. Good breeders can explain to you how they use these numbers and why—not so good breeders will show you low RC and IC percentages and breed affected dogs. Hopefully now you will be able to see the difference.

Now we have to ask ourselves why breeders would toss out RC and IC percentages? Genetic diversity proponents believe low numbers afford a healthier gene pool. We already know the probability of “inheritance by descent” can work for you or against you. If you have a gene pool that has more than its share of problems, you might want to work for more diversity through outcrossing. When you outcross it automatically lowers your IC and RC numbers because an IC measures the degree to which an animal is inbred and RC measures the probability of inheritance by descent based on the relationship between two animals (or a collective of the pedigree). You can have an RC value with no inbreeding whatsoever and although an IC is informative on its own, its value is greatly increased when you combine the IC with an RC so you know which ancestor genes are concentrated in a pedigree. So an ethical breeder could use IC and RC percentages along with line research on health and temperament to enhance his or her breeding program. An unethical breeder could use low RCs and ICs gained through the use of an outcross program and market litters as having hybrid vigor and genetic diversity. In effect, the RC and IC numbers are nothing more than a marketing tool for this type of breeder. Worse yet, the unethical breeder could breed affecteds or known carriers and still have low IC and RC percentages which could be used to impress potential puppy buyers or people interested in purchasing dogs to breed. This of course would wreak havoc on the gene pool--especially a small gene pool.

What can breeders do? Breeders can get better educated on the application and use of breeding statistics. They can make data regarding their lines more easily accessible to other breeders and to buyers. Most importantly, breeders should not depend on statistics without a thorough examination of the line’s health and temperament when making a decision about breeding two dogs. In my research I ran across a great article entitled “Breeding Notes” on a Lhasa-Apso site. I wish I could acknowledge the author (I could not find a name). It is a short, to the point “list” of “how to’s” for understanding the difference between “stupid breeding and intelligent breeding.” I highly recommend it to anyone new to breeding or a breeder looking for ways to improve. It can be found here: http://www.lhasa-apso.org/health/howto.htm I have also listed my references for this article that breeders may find informative.

What can buyers do? Buyers can get smarter on what the statistics breeders toss around mean. Buyers can determine for themselves whether they are getting misled or not. Hopefully this article is one step in that direction. Buyers can also apply common sense to the puppy buying process and understand that you can have a low IC and/or a low RC and if the sire and/or dam (or grandparents) is affected with a genetic disorder (hip dysplasia, EPI, elbow dysplasia, heart problems, etc.)—an IC or RC of 0 is not going to give you a healthy, stable puppy. A low IC or RC is not going to minimize your risk of inheriting said genetic disorder. What will minimize your risk is knowing what is in the dogs themselves that led up to your prospective puppy. I have listed several references for this article, but buyers do not need to know all the ins and outs of breeding or how to calculate breed statistics. However, smart buyers do need to know what is behind the numbers (what the numbers mean) that are thrown at them when they are researching a litter—it is a matter of common sense and minimizing risk. Not all breeders are created equally and the old adage “buyer beware” is as true today as the day it was created. Do not be impressed by low IC and RC numbers alone—know what is behind the lines of a potential puppy! You owe it to yourself, your family, and your checkbook.

^{1http://www.breedmate.com/inbreeding.htm}

²nbii Population Genetics

For more information on RC and its application:

http://www.wolfweb.com.au/acd/itsallinthegenes.html

http://www.canine-genetics.com/relation.htm

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