S.L. Kacirek, P.I. Dimsoski, K.M. Irvin, and S.M. Moeller
Department of Animal Sciences
The Ohio State University
Columbus, Ohio 43210
Historical evidence shows that the Large White breed was developed in 18th century England in the county of York, where at this time it was called the Yorkshire breed. Later, the name was changed to the English Large White. The Large White is thought to be a combination of the Leicester, Berkshire, Chinese Neopolitan, and Essex breeds. It wasn't until the 19th century that the Large White was imported into the United States. In the U.S., the Large White breed is also registered as the Yorkshire breed. The U.S. and English lines have had limited contact until recently when Large Whites were imported into the U.S. Because the two breeds were developed under selection schemes practiced in their respective countries, these two breeds could represent different gene pools.
The primary objective of this study is to examine the genetic similarities or differences of the Yorkshire and Large White breeds based on microsatellite variations that exist in the two populations. If the allelic frequencies of the microsatellite loci are found to be significantly different in the Yorkshire and Large White breeds, we can conclude that the two populations diverged from one another and represent two distinct populations.
Materials and Methods
Thirty individuals of each breed were chosen according to least relatedness criteria. Eighteen dinucleotide microsatellites were randomly chosen for analysis. DNA was extracted from blood samples and amplified by the Polymerase Chain Reaction (PCR). Amplification was confirmed on agarose minigels. Samples were loaded into 6% polyacrylamide sequencing gels, and the DNA bands were detected by silver staining. The size of the DNA bands were determined by comparing them to known (100 bp ladder) size bands. Allelic frequencies were estimated by direct counting. Calculated genetic parameters include: heterozygosity levels, the exact test of Hardy-Weinberg equilibrium, Fst values, test for distribution of allelic frequencies, and genetic distances.
Preliminary results indicate that the Yorkshire and Large White breeds, due to many generations of selection, diverged enough so that their differences were significant enough to be measured by microsatellite variation. Due to the variation in the populations, it appears that the Yorkshire and Large White breeds represent two distinct populations. Other ongoing studies at The Ohio State University are focusing on the degree of relationship between the two breeds. The first project examines performance characteristics (sow productivity, growth, feed utilization, and carcass qualities) of various combinations of crosses of Yorkshire, Large White, and Hampshire pigs in order to determine the presence and magnitude of individual and maternal heterosis. The second study examines the allelic frequencies of the microsatellite loci in the Hampshire breed. The Hampshire breed was selected because it is unrelated to and evolved under different selection schemes than the Yorkshire and Large White breeds. These results will be used as a reference point to help in more clearly defining the relationship between the Yorkshire and Large White breeds.
If we are able to demonstrate that the Yorkshire and Large White populations diverged from one another, then there are some implications for the swine industry to consider. What effect has there been with the Yorkshire and Large White breeds being registered in the same association? How much of the excellent performance found in the Yorkshire and Large White breeds is due to heterosis, and how may this change future selection practices?