Coefficient of Inbreeding

author Sara Thornton DVM                           iCandy RagaMuffins

What is a coefficient of inbreeding  (COI) and why is it important? The COI is a measurement of the amount of inbreeding in a specific population. In my case, the population of concern is the RagaMuffin breed of cats. According to  COI FAQS: Understanding the Coefficient of Inbreeding by Carol Beauchat PhD, “The coefficient of inbreeding is the probability of inheriting two copies of the same allele from an ancestor that occurs on both sides of the pedigree.”

Why is it important to know what the COI is in every breeding? Especially in a limited population like RagaMuffins, calculating the COI is one tool to maintain the health of the breed. A high coefficient is more likely to reproduce qualities that are not desired, thereby decreasing vitality and health of the breed. Think about it this way, sibling pairs or parent-offspring pairs are generally avoided in order to prevent genetic issues. But, in order to truly evaluate a pairing, it is important to go further back in a pedigree. Geneticists recommend evaluating using ten generations.

So, how does a breeder check the COI on a prospective pair? It’s simple, I use a computer program that has much of the RagaMuffin population history stored in it. The data lists cats from the very beginning- including random bred cats, Persians, Ragdolls, and Siberians along with a lot of RagaMuffins. More recently, Selkirks have been added as they are a permitted outcross in CFA. The main chore I have is to keep it updated as more cats join the breeding population of muffins. I input the names of the cats I want to breed, select ten generation inbreeding analysis and click!

My goal is to keep the coefficient under 10% as the geneticists generally recommend. That being stated, does not mean I would not utilize a higher number. As line breeding can produce harmful qualities, it can also increase the incidence of positive traits.  That is the art of being a breeder….figuring out what traits I want to avoid and what traits I want to ensure are reproduced. Health is number one. I do the genetic testing to give my kittens the best shot at a long and healthy life. By being cognizant of the COI, I can reduce the incidence of characteristics I want to avoid.

What happens if breeders do not utilize a coefficient of inbreeding? It seems so many do not understand  that a brief pedigree cannot be eyeballed and deemed safe. For three or four generations, there may be no replication of breeding animals, but further back, there could be substantial replication which leads to a high COI. This is of special concern in a smaller population in a rare breed.