To investigate the influences of candidate genes on the birth weight and the early stages of life, genotyping of the prolactin receptor 3 (PRLR3) and retinol-binding protein 4 (RBP4) genes was performed in 156 and 141 Berkshire pigs, respectively. The frequency of both PRLR3 alleles A and a was 0.50. The frequencies of the RBP4 alleles B and b were 0.42 and 0.58, respectively. Neither locus was in Hardy-Weinberg equilibrium. No significant associations of the PRLR3 alleles with birth or weaning weights and of the RBP4 alleles with birth weight were observed. The proportions of the phenotype variances due to the genotypes of PRLR3 in the feeder weights was 4.0% and those of RBP4 in the weaning and feeder weights were 11.9 and 3.3%, respectively (P < 0.05). The dominance effect of PRLR3 and RBP4 on feeder weights was 2.40 and -1.86 kg, respectively (P < 0.01). The additive and dominance effects of RBP4 on weaning weights were 0.332 and -0.682 kg, respectively (P < 0.01). Even if no significant epistasis of PRLR3 and RBP4 was detected, a considerable trend of consistent positive epistasis estimates of AA/BB and Aa/Bb was observed for all traits. The results of this study may have a considerable impact on early-stage growth by both loci, and a selection strategy should be designed separately for each marker in Berkshire pigs.