Many of the sheep breeds found in the United States are being developed through a technique called upgrading.
The United States (and many European countries) have strict regulations on the importation and exportation of live animals and particular sheep breeds. As a result, there are many wonderful breeds that can’t be brought into the United States, like Gotland, Teeswater, Herdwick, BFL and Black Welsh Mountain. And yet, there are American flocks of all these breeds!
While we can’t import these sheep, we can import semen. A breeder will choose a breed that is close to the breed they want. For example, if a breeder wants Teeswater, he or she might choose another longwool breed like Leicester Longwool. A Leicester Longwool ewe is inseminated with semen from a Teeswater sheep. The result is a 50/50 genetic blend. This second generation sheep is then inseminated with Teeswater semen. The resulting lamb is 75/25 Teeswater. This process is continued until the sheep being bred are primarily Teeswater genetics.
An upgraded flock will never be 100% genetically the same as the original breed. American Teeswater may be 95-99% Teeswater. But chances are you or I would not be able to tell the difference unless one population or the other were heavily modified.
Upgrading is one way we can help preserve breeds and populations that are rare or threatened. Sometimes there aren’t enough sheep left in a population to have sustainable genetic diversity.
Check out Deb Robson’s video on rare breeds for more information.