The complexity and identity of the metabolic processes in the digestive tract of ruminants impose strict requirements on the quantity and quality of nitrogenous substances in the diet. The increase in skeletal muscle mass is associated with the processes of protein synthesis and breakdown in the body. The direction of metabolic processes towards increasing the protein biosynthesis of the body is ensured by a sufficient supply of amino acids from the gastrointestinal tract to the metabolic pool of the body by optimizing the energy protein nutrition of ruminants. The purpose of the work is to study the effect of the level of metabolic protein in the diets of Aberdeen Angus bull calves on the bioconversion of metabolizable energy and amino acids into growth energy. The study involved the sequential conduct of 3 series of studies on bull calves of the Aberdeen Angus breed with a live weight of 277 kg, 317 kg and 363 kg. The animals of the 1st experiment were fed according to the RAAS (Russian Academy of Agricultural Sciences) standards, where the ratio of the metabolizable protein to the metabolizable energy was 8.2 g/MJ, in the 2nd and 3rd experiments the level of the metabolizable protein was 8.6 and 9.1 g/MJ per the introduction of 0.5 kg and 0.6 kg of soybean meal into the diet, respectively. At the end of each period, physiological experiments were performed. The studied parameter did not have a significant effect on the dry matter intake of the feed, and an increase in the diet of hard-to-break down protein contributed to an increase in the concentration of metabolizable energy and digestibility of dry matter. It was found that metabolizable energy and amino acids are effectively used to increase the live weight of bulls calves during the growing period on a diet in which the ratio of metabolizable protein to metabolizable energy is 8.6 g/MJ. A further increase in metabolic protein in the diet leads to an increase in heat production, which in turn increases the use of amino acids and metabolic energy in energy metabolism and reduces their contribution to the increase in live weight.