Some Thoughts on Inbreeding “Co-efficients”

About the time the Burmese breed descended into inbreeding related ill health, someone devised calculators that could determine how inbred your Burmese cat was. And, you could use these same calculators to test out matings, before the matings occurred, to determine how inbred the kittens would be. These calculators spit out an “inbreeding co-efficeints”.

And breeders and consumers alike began using these “inbreeding co-efficients” as a marker of how inbred the cat they were about to breed or buy was. The thought being that if the cat had a high inbreeding co-efficient, that was bad. The cat was inbred. If the cat had a low inbreeding co-efficient, that was good. I was one of those breeders. I used the calculators to make breeding decisions, aiming to have the lowest inbreeding co-efficients possible.

Make no mistake, I love me some calculations. They appeal to my inner scientist. My breeding pal, Sue Dado and I would work those calculators and work those calculators. All in the aim of figuring out how we could breed cats with a zero inbreeding co-efficient. Because zero inbreeding was better than say 35% inbreeding? Right ?

Sue and I both tried to make cats, from American Burmese, with zero inbreeding co-efficients. When I started importing Thai Burmese cats, those calculators really started spitting out a lot of 0% inbreeding co-efficients. That was super exciting.

One of my mentors was Phyllis Wilson of Incapaisley Cattery. She was a tough broad and often said, “those inbreeding calculators are none sense and their outcomes worthless”. It’s the kind of thing Phyllis would say. “Look at the pedigrees.” Phyllis has gone to the big cat show.   I miss her every week . I want to call her and get her opinion and then remember I cant. She was smart and had common sense. And she would just lay it out there with no bow or ribbon.

In any event, per Phyllis suggestion, I started looking at Burmese pedigrees. Courtesy of the fabulous online Burmese Pedigree database maintained by some saintly folks unknown to me. The database made it  possible for me to trace my cats back to the cats that were used to start the breed.

My foundation American cats came from four breeders that did not share any cats. To mind, they were unrelated American Burmese cats. They came from OkeyDokey cattery, Madame Butterfly cattery, Laki Cattery, and Incapaisley Cattery. Using the calculator, if I bred a Laki cat to a Incapaisley cat, the calculator gave me a 0% inbreeding co-efficient. I did not question the outcome.

However, when I looked at the pedigrees of the two parents that produced the kittens with a 0% inbreeding co-efficient, I found something interesting. Both cats were the direct descendent of the two cats used to start the Burmese breed in America, Wong Mau and Tai Mau. So my Laki cat, direct descendent of Wong Mau and Tai Mau, bred to my Incapaisely cat, direct descendent of Wong Mau and Tai Mau, somehow produced an inbreeding co-efficient.

Bear in mind, the Burmese breed is a closed breed. That means all the Burmese cats in the country descend from Wong Mau and Tai Mau. ALL. No exceptions. And, if you take the time on the Burmese pedigree database to keep going backwards on any American Burmese cat, you will end at Wong Mau and Tai Mau.

And this goes back to the point Phyllis made, which at the time made no sense to me, the calculators are of no value in determining inbreeding. If you look at the pedigrees, they all descend from the same two cats. As such,  all American Burmese are 100% inbred. This thing called MATH makes it impossible for anything else to be true.

How can these calculators produce these false inbreeding co-efficients? They don’t go far back enough in time. While it may be true that within 8 generations, my Laki cat appears to be unrelated to my Incapaisley cat, if you go back 30 generations, you find they both descend from the same two cats. So when I am breeding my Laki cat  (Wong Mau x Tai Mau)  to my Incapaisley cat(Wong Mau x Tai Mau), it is simply impossible to come up with a 0% inbreeding co-efficient.

Like Phyllis Wilson said, the calculators are worthless. Look at the pedigrees. And, if you look at the pedigrees, and realize the whole damn breed descends from two cats, it is no wonder the breed is having health problems. Really, the mystery is why it took so long?

I can’t even say that and my cats are all half imported Thai Burmese. Because they are also American Burmese. And because my American Burmese are 100% inbred. Divide 100%  by two, and you are at a 50% inbreeding co-efficient. So, I am here to say it is statistically impossible for someone to breed two American Burmese and end up with a real zero inbreeding co-efficient.

Play games with your mind as you like, but, the math just does not add up.

I would strongly suggest breeders put down the calculators and start looking at the pedigrees. And, for consumers, when a breeder says they have a 0% inbreeding co-efficient, ask how?