The aim of this study was to determine the effect of complete diets containing different levels of crude protein and limiting amino acids fed to pigs in a two-phase feeding system on protein digestibility and N retention, utilization and excretion to the environment. A digestibility-balance trial was conducted using 24 growing-finishing pigs (hogs) divided into 3 groups. The animals were housed individually in metabolism crates and were fed diets: C - standard levels of protein and essential amino acids, R - protein and amino acid levels reduced by 15% relative to the standard levels, R+AA – reduced protein content and supplementation with crystalline lysine, methionine, threonine and tryptophan to the standard levels (as in diet C).  Grower and finisher diets in which the levels of crude protein and total lysine were reduced by 15% fed to pigs in a two-phase feeding system decreased (P≤0.01) protein digestibility. However, a significant reduction in urinary N excretion and improvement in N utilization, relative to both N intake and N digestion (P≤0.05), were noted in this group. The supplementation of low-protein diets with crystalline essential amino acids improved protein digestibility, N retention and N utilization. According to estimates, a 15% reduction in crude protein (i.e. 2 to 2.5%) and amino acids concentrations in growing-finishing pig diets, relative to the standard levels, reduced N excretion to the environment by 18.7%. The supplementation of low-protein diets with essential amino acids contributed to a further reduction in N excretion to 22.5%. The results of this study indicate that the crude protein content of complete diets for growing-finishing pigs, in two-phase fattening, can be reduced by 2-2.5% relative to the standard level for this type of compound feed. However, enrichment of low-protein diets for pigs with lysine, methionine, threonine and tryptophan to the standard level remains a necessary condition.

25.2.2020