The objective of the studies was to evaluate the impact of the prolactin receptor and β-casein genes on the basic chemical composition and pH of the colostrum and milk of sows. Experiments were carried out on 103 Złotnicka White breed sows. These animals are under the Domestic Program of Protection of Genetic Resources. Analysis of the influence of polymorphism in the PRLR and CSN2 loci revealed that sows of the TT homozygote were characterised by the highest drymatter content. Analysis of polymorphismin the PRLR locus for protein showed that the highest values were in milk of sows of the TT genotype, and GG homozygotes in the case of the CSN2 locus. Inference of the impact of polymorphism in the PRLR and CSN2 loci on the fat and lactose content of sow milk demonstrated considerable variability. These differences were statistically significant at the level of α = 0.01 and α = 0.05. Periodical changes in individual pH values were apparent for particular genotypes in both loci (PRLR and CSN2). The perceptible changes that occurred between individual genotypes were statistically significant at the levels of α = 0.01 and α = 0.05. The investigations confirmed that the nutritive values of sowcolostrumandmilkwere determined by genetic factors. This issue warrants comprehensive analysis, especially in terms of evaluation of the breeding value of maternal breeds.