SUMMARY
The growth and development of pigs is determined by their genotype and environmental conditions (primarily the level of feeding), however, the number of works aimed at studying the complex influence of genetic and non-genetic factors in their interaction is currently insufficient. The purpose of our work was to estimate the effect of the MC4R genotype, feeding level and interaction of these factors on growth and backfat thickness of crossbred pigs and to investigate the possibility of correcting the melanocortin-4-receptor gene polymorphism effect by adjusting the ration. Studies were conducted on 50 gilts obtained by crossing sows of the large white breed with landrace boars. Experimental pigs at the "Maxi 2010" farm were weighed at birth, then at the age of 28 days (at weaning) and at the age of 4, 6, 8 months. Fat thickness was measured at the age of 4, 6, 8 months. Genetic studies were conducted in a certified laboratory of Institute of Pig Breeding and Agroindustrial Production. Analysis of 50 blood samples revealed that this group of pigs had a sufficient level of polymorphism for research (Polymorphism Information Content was equil 0.35). The frequency of genotype distribution at the MC4R / SNP c.1426 G>A locus was 0.06 (AA) : 0.58 (GA) : 0.36 (GG). The type of feeding significantly influenced the live weight at the age of 4 months and the average daily gains of experimental pigs over the period of 28–120 days. Starting at the age of 6 months a significant effect of the interaction of organized factors (feeding + genotype) was recorded. At the age of 6 months, a significant influence of both the genotype and the level of feeding on the backfat thickness was established. Animals with the GG genotype receiving a restricted feed ration had significantly lower backfat thickness. At the age of 8 months, the difference in backfat thickness between the group with the GG genotype (restricted feed ration) and the AG genotype (high level feeding) reached a value of 12.9% (2.0 mm). Animals with the AG genotype had the lowest performance and the greatest fat thickness under feed limitation, which is important for raising young pigs for subsequent reproduction. Therefore, when selecting pigs to be used for further reproduction, the desired genotype is GG. In the future, it will be desirable to repeat the study on a larger number of pigs, so that the experiment involves a sufficient number of animals with the MC4R AA genotype for statistical processing.