The objective of this study was to find out candidate genes associated with litter size trait in pigs of inbred Large Yorkshire and Landrace populations. 86 sows were screened for candidate genotypes along with litter size data recordings. Association of litter size with genotypes of candidate genes were investigated to verify the usefulness of each gene's genotypes as markers for the trait. For the lines of Large Yorkshire, PRLR3 and RBP4 genes were genotyped. Frequency distribution of PRLR3 with genotypes AA, AB and BB were each 0.14, 0.44 and 0.42. And the average litter size by PRLR3 genotypes were 8.83, 10.81 and 10.70 piglets per litter, the average estimated breeding values of which were 0.243, 0.332, 0.365, respectively for AA, AB and BB genotypes. Genotypic frequencies of RBP4 by AA, AB and BB genotypes were 0.10, 0.44 and 0.46. The average litter size by genotypes of RBP4 were 10.40, 10.57 and 10.35 piglets per litter and their corresponding average estimated breeding values were 0.451, 0.353 and 0.261, respectively for genotypes AA, AB and BB. Significance in differences among genotypes were not observed, but B allele of RBP4 seems to be associated with litter size. In Landrace lines, frequencies of RBP4 genotypes, AA, AB and BB were 0.29, 0.55 and 0.16. And the average litter size of these genotypes were 10.50, 11.08 and 11.00 piglets per litter. The corresponding averages of estimated breeding values of each genotypes were 0.172, 0.135 and 0.104. In Landrace lines, allele A was more likely to be associated with litter size, even if differences among average litter size were not significant. We conclude that genotyping of two candidate genes is a helpful tool to identify genetic potentials of litter size in pigs.

The relationship of several candidate genes polymorphisms with breeding values of economic traits were investigated in Korean Native Pigs. Record (2001-2006) of 546 Korean native pigs were obtained from National Institute of Animal Science, Korea having data on average daily gain (ADG), age at 70 kg (D70 kg) and backfat thickness (BF). The data's obtained were analyzed by the DF-REML (Derivative-Free Restricted Maximum Likelihood) program of Boldman using a single-trait animal model to analyse the genetic parameters. The analysis of restriction fragment length polymorphism (RFLP) was conducted on 68 Korean native pigs (KNP) using single nucleotide polymorphism (SNP). Different genotype frequencies of 5 candidate genes such as MC4R, PRKAG3, FABP3, ESR and PRLR3 were observed in KNP. Significant relationship of AA and AB genotype between MC4R polymorphic site and breeding value for average daily gain (ADG, p<0.05) was observed. PRKAG3 polymorphic sites were also found to be significantly related to breeding values for ADG, AA, AB genotype (p<0.05) and also, for Backfat thickness (BF), days to 70 kg and BB genotype (p<0.05). In conclusion, selection method would be more effective if it encompasses significant genotype for performance traits and that would further aid in the selection of seed stock in KNP.