INBREEDING AND RELATIONSHIP FOR THREE BREEDS OF PIGS IN CANADA

Abstract

Pedigree sampling techniques were used to study inbreeding and relationship within the Berkshire, Yorkshire and Tamworth breeds in Canada. The pedigrees sampled were from Volume 71 of the Canadian Swine Breeders Herdbook published in 1963.The Berkshire is the oldest established breed in Canada, but in terms of genetic relationships it is the youngest of the three breeds studied. Only two of the important ancestors of the breed predate 1939. A high proportion of the inbreeding present in the breed has also occurred since that date, and the major importations of breeding stock have taken place since 1948.The Yorkshire, established in 1889, 13 years after the Berkshire, has been markedly less dependent on importations. Inbreeding has progressed at a reasonably steady rate since 1920 and birth dates of important common ancestors of the breed are distributed reasonably uniformly over the period from 1900 to 1940. These two breeds have the same inbreeding (7.0%), but, because of the difference in effective genetic age, inbreeding in the Berkshire has progressed at approximately double the rate per generation observed for Yorkshires. Inbreeding of the Tamworth has progressed at a rate comparable with the Berkshires. In terms of generations, however, the breed is of essentially the same age as the Yorkshire and total inbreeding is approximately double that for the Yorkshire and Berkshire breeds.