Level of Inbreeding in Yorkshire, Landrace, and Hampshire Breeds

Purdue University 1995 Swine Research Report. Inbreeding is a measure of the common ancestry of the parents of an animal, and ranges from 0 to 1 (or 100%). If a sire and dam are related (have genes in common through common ancestors), then their progeny are inbred. The level of inbreeding depends on how strongly related the parents are. Inbred animals are more homozygous than noninbred animals; that is, they have the same alleles (form of the gene) on both chromosomes for a locus (gene location). High levels of inbreeding generally will result in decreased performance, particularly for reproductive traits. The occurrence of these problems tends to become apparent at levels of inbreeding above 15%, and becomes progressively more severe as inbreeding increases. Breeders who are trying to improve their herds with performance testing and Expected Progeny Deviations (EPD) often find that the best animals are related to one another. As these superior animals are mated to each other, average inbreeding in the herds will tend to increase, and it eventually may become difficult for the breeders to avoid high levels of inbreeding. This study examined the amount of inbreeding, and the change in inbreeding over time, in the Yorkshire, Landrace, and Hampshire breeds.