Leucine and valine supplementation of low-protein diets for broiler chickens from 21 to 42 days of age

The objective of this study was to determine the requirements and interactions between the standardized ileal digestible (SID) Leu and Val levels in low-protein diets, and their effects on performance, serum characteristics, carcass yield and diameter of muscle fibers of broiler chickens from d 21 to 42 posthatch. A total of 1,500 21-day-old Cobb 500 male broiler chickens were distributed in a completely randomized design in a 5 × 5 factorial arrangement for a total of 25 treatments with 3 replicates of 20 birds each. Treatments consisted of 5 SID Leu levels (1.0, 1.2, 1.4, 1.6, or 1.8%) and 5 SID Val levels (0.52, 0.67, 0.82, 0.97, or 1.12%). At 42 d of age, there was interaction (P