In recent years, based on new scientific data, many countries worldwide have been revising the existing standards for introducing trace elements in mixed feed for highly productive broiler chicken crosses. This also applies to selenium, which is recognized as an indispensable biotic ultramicroelement with a wide range of biological action according to modern classification. However, some aspects of the selenium effects on poultry have not been elucidated yet. We have conducted comprehensive research to deepen and expand modern ideas about the biological role of selenium, its impact on the interior and productive qualities of broiler chickens in the post-embryonic period of ontogenesis. One of the tasks was to study the causal relationship between the level of selenium consumption by broiler chickens and the studied indicators. The research was conducted on broiler chickens of the Cobb 500 cross. During the rearing period, the feeding of broiler chickens of all groups was carried out with dry full-fledged mixed feeds following the existing norms. The poultry of the first control group did not receive selenium supplementation. The poultry of the second experimental group was additionally injected with Selenium at the rate of 0.2 mg/kg, the third of 0.3, and the fourth of 0.4 mg/kg. When conducting a correlation analysis of the obtained experimental data, it was found that there are different levels and directions of relationship between internal and economically valuable features included in the study, which may vary depending on the selenium content in mixed feed for broiler chickens. A scheme of modeling the effect of selenium on broiler chickens’ bodies is proposed.