Why Does Inbreeding Matter?

As a group of rare pig breeders, we have reached a stage where we have a large enough population of Large Black pigs, dispersed across North America, to be more selective in our breeding programs. In the past you were lucky just to get a breeding pair; now there is enough diversity, and documentation of that diversity, for us to be more concerned with the health of the genetics of our breed. To be responsible breeders we need to now include the amount of future inbreeding in our herds as much as any other factor.

If you have been a breeder of registered dogs, cats, cattle or goats, you already understand what the Coefficient of Inbreeding (CI) means and its historical and scientific basis. A simple explanation of Coefficient of Inbreeding is that it measures the amount of inbreeding present in a single animal. The higher the CI, usually expressed as a percentage, the higher the amount of inbreeding. A 25% CI is equivalent to mating half-siblings. You may get 30% or 40% or higher CI mating brother to sister depending on how inbred the parents are. A CI of 10% or less is considered to be good for a rare breed.

Why does inbreeding matter? When you mate two animals that are closely related there is a high probability that certain traits are passed on to their offspring. These traits may be beneficial, such as a large amount of functional teats, or they may be detrimental, such as a susceptibility to certain diseases or internal parasites.

Being aware of genetic diversity is critically important for any rare breed. One of the best ways to keep diversity in the breed is to keep more males as breeding stock, rather than using AI semen that comes from one or two boars. If everyone uses the same boar or its semen, no matter how great he is, the breed loses the diversity of the genetic material that is so critical. Resist using AI (artificial insemination) except for importing some genetics you can’t get otherwise.

This is where the CI of our animals becomes useful. When making a decision of which boar to breed to which sow you can calculate the expected CI of their offspring. A simple plan would be to shoot for a CI of 20% or less; the lower, the better.

So how do you know what will make a good breeding mate for your pigs? The answer is not simple, but calculation of the CI is a start. As the Registrar for the Large Black Hog Association I can calculate the CI for any Large Black hogs to which the Association has the pedigree information. Just email me with your request.

– by Brian Wright
Portions copyright © 2010 Homegrown Acres. Used with permission.