Maintenance lysine requirement and efficiency of using lysine for accretion of whole-body lysine and protein in young chicks

Two bioassays were conducted to determine the maintenance requirement and e fficiency of utilization of dietary Lys in young chicks. New Hampshire x Co lumbian males were used in Assay 1 and Avian x Avian males were used in Ass ay 2. In each assay, chicks were given free access for 10 d to crystalline amino acid (AA) diets containing graded levels of L-Lys.HCl. Doses of Lys r epresented 5, 40, 55, 70, and 95% of its ideal level in Assay 1; all other AA were set at 100% of their ideal levels, except for the lowest Lys level, in which the other AA were maintained at a 15% excess. Ln Assay 5 doses of Lys represented 5, 10, 40, 55, 70, and 95% of ideal; all other AA were mai ntained at minimized excess levels that were 15% (of ideal) above the vario us doses of Lys. After 24 h of feed deprivation, chicks were killed for who le-body protein and AA analysis. In Assay 1, protein accretion (r(2) = 0.95 ) and Lys accretion (r(2) = 0.98) were Linear (P < 0.01) functions of Lys i ntake. Slope of the Lys accretion regression line indicated that 75.8% of t he crystalline Lys ingested (above maintenance) was retained. The Lys requi red for zero protein accretion was 12 mg/d or 45 mg/d per kg(3/4) whereas t he Lys required for zero Lys accretion was 30.3 mg/d or 114 mg/d per kg(8/4 ). With Avian x Avian chicks, protein accretion (r(2) = 0.99) and Lys accre tion (r(2) = 0.99) were linear (P < 0.01) functions of Lys intake. Slope of the Lys regression indicated that 79.3% of the Lys ingested was retained. The Lys requirement for zero protein accretion was 2.5 mg/d or 6.9 mg/d per kg(8/4). The Lys maintenance ment for zero Lys accretion, however, was 32. 3 mg/d or 89.1 mg/d per kg The data demonstrated that at nitrogen equilibri um, chicks are in negative Lys balance are in positive balance of glycine a nd proline.