Partition of Amino Acids Requirement for Maintenance and Growth of Broilers I. Lysine

Purified diets containing five graded levels of lysine were fed to a total of 125 growing chicks (25 chicks per treatment) to evaluate lysine requirements for growth and maintenance. A model was developed to separate lysine requirement for maintenance from requirement for growth. Based on weight gain response, the daily lysine requirement for growth was 12.06 mg/g gain and the daily lysine requirement for maintenance was 0.332 times metabolic body size ($W^{0.75}$). Similarly, the lysine requirement for growth was 0.457 mg/mg nitrogen gain and the daily lysine requirement for maintenance was 0.344 times metabolic body size. The plateau of plasma lysine concentration was reached at 354.75 mg intake/day. The total lysine requirement was 414.27 mg/day or 1.0% of the diet, 420.11 mg/day or 1.01% of the diet based on weight gain response and N gain response, respectively. Previous lysine requirements for growing chicks of 1-28 days old were in close agreement with these estimates. As a percentage of protein, lysine requirement was calculated to be 7.3% and the reported lysine content of chick muscle crude protein of 7.46% was closely related.