Leucine Requirement of Female Cobb Broilers from 8 to 14 Days of Age

The objective of this study was to estimate the optimum requirement of the digestible leucine in ratio to lysine in female Cobb 500 broiler chicks from 8-14 days of age. In this study, 540 female broiler chickens (Cobb 500), were allocated to the experimental units in a completely randomized design with 6 treatments of 6 replicate pens of 15 birds in each. A basal diet (2890 kcal apparent metabolizable energy corrected for nitrogen (AMEn)/kg; 19% crude protein) was formulated to provide all of the nutrients with the exception of leucine. Lysine was sub-limiting and provided at 90% of recommended level of digestible lysine. Crys-talline L-glutamic acid in basal diet was replaced by crystalline L-leucine to provide experimental diets containing 0.93, 0.98, 1.03, 1.08, 1.13, and 1.18 digestible leucine in ratio to lysine. Performance parame-ters were evaluated during a 7-day period (d 8-14) of ad libitum feeding. The body weight, weight gain and feed intake were significantly influenced by dietary treatments and showed quadratic effect with increasing digestible leucine in ratio to lysine. The groups fed 1.03 and 1.13 digestible leucine in ratio to lysine diet had statistically (P<0.05) greater feed intake than the group fed 0.93 digestible leucine in ratio to lysine diet. The birds fed 1.13 digestible leucine in ratio to lysine diet had higher body weight and weight gain (P<0.05) than the birds fed 0.93 digestible leucine in ratio to lysine diet. Using the curvilinear-plateau model and the quadratic regression analyses, the requirement of digestible leucine to lysine ratio for maxi-mum feed intake were estimated as 1.05 and 1.04, respectively. The curvilinear-plateau model and the quadratic regression analyses estimated the requirement of digestible leucine to lysine ratio for maximum weight gain to be 1.07 and 1.06, respectively. However, the curvilinear-plateau model estimated the re-quirement of digestible leucine to lysine ratio for the minimum feed conversion ratio at 1.11. Based on the analysis of obtained data, female Cobb 500 broilers need lower ratio of leucine to optimize feed intake and weight gain than feed conversion ratio. In conclusion, the requirement of Cobb 500 female broilers from 8 to 14 d of age to support performance parameters was 1.08 digestible leucine in ratio to lysine.