Performance of broiler chicks fed various levels of dietary lysine and crude protein

An experiment was conducted to establish a basal diet deficient in both protein and lysine. The responses of broiler chicks to graded levels of lysine at two levels of CP were measured in diets mixed by two experimental methods (diet dilution and graded supplementation). Experiment 1 had a 2 x 3 factorial arrangement of treatments with three dietary CP levels (17, 20, and 23%) and two levels of lysine per CP level (35 and 48 g lysine/kg CP). Dietary CP and lysine levels had significant (P < 0.001) effects on body weight gain (BWG), feed intake, and feed conversion ratio (FCR). In exp. 2, the lysine requirement of chicks (9 to 18 d of age) was estimated at two levels of CP in diets mixed by the diet dilution method. The requirements for lysine at 17% CP (as a percentage of CP) were estimated to be 4.45 +/- 0.18% for BWG (R2 = 0.83) and 4.33 +/- 0.16% for FCR (R2 = 0.81). Similarly, the requirements at 23% CP were 4.34 +/- 0.16% for BWG (R2 = 0.84) and 4.35 +/- 0.13% for FCR (R2 = 0.89). In exp. 3, the lysine requirement of chicks (10 to 18 d of age) was estimated at two levels of CP in diets mixed by the graded supplementation method. The requirements for lysine at 18.5% CP were 5.17 +/- 0.25% for BWG (R2 = 0.80) and 4.26 +/- 0.15% for FCR (R2 = 0.85). Similarly, the requirements at 23% CP were 4.59 +/- 0.17% for BWG (R2 = 0.83) and 4.71 +/- 0.16% for FCR (R2 = 0.88). Results of a t-test show that the requirements were not significantly different between the two CP levels for BWG in experiments 2 and 3 (P < 0.05). It is concluded that the amino acid requirements of broilers are a constant proportion of CP levels at least in the range of CP levels commonly fed.