The weight of newborn piglets in domestic pigs depends on the maternal environment. Using an original algorithm based on the comparison of the coefficients of correlation between the half-nests (the same average genotype and the same conditions of the embryonic environment) and the twin sockets (the same genotype, different conditions of the embryonic environment), it was possible to estimate the relative contribution of the various components to the weight of the newborn in the domestic pigs. Our investigation found that the relative contribution of environmental conditions during prenatal development into newborn weight variation is equal to 0.4717, the contribution of genotypic component is 0.4032; the contribution of interaction between environmental conditions and ambivalence of the “genotype–phenotype” relationships is 0.0846, indeterminacy of phenotypic realization of the littermate’s genotypes is 0.0405. Maternal resource plays the main role amongst factors forming the environmental conditions of prenatal development. The gene pool will remain unchanged in any number of generations, despite a change in the population parameters of the trait. In principle, it can be assumed that when a population reaches a certain level, when the mean value of the trait and the gene pool are optimal (the selection pressure vectors are mutually balanced), selection becomes less effective in transforming the average phenotype than changing environmental conditions. Obviously, therefore, livestock maintenance and feeding are paid as much attention as breeding, and breeds of farmed animals are zoned
