One thousand eight hundred and ninety male broilers of two strain crosses (fast and slow initial growth) were fed different ideal protein profiles in four-phase feed programs: 1 to 7, 8 to 21, 22 to 34 and 35 to 40 days of age. All vegetable, corn-soybean meal feeds were formulated to maintain the Met+Cys:Lys and Thr:Lys relationships at 75 and 65%, respectively, on true digestible basis. Three ideal protein profiles were used: low, medium and high. From 1 to 21 days of age, half of the birds fed low and high diets were changed to high and low diets, respectively. Birds on the medium diet were kept on the same diet until the end of the study. A 3 × 2 (ideal protein profile x strain cross) factorial design was used for the period from 1 to 21 days and a 5 × 2 design thereafter. Carcass and commercial cuts were performed at 34 and 40 days of age to determine corresponding live weight and carcass yields. In general, the fast strain growth was superior in comparison to the low one when live performance and carcass and commercial cuts were evaluated. Live performance was positively affected by the increases in the dietary protein profiles; however, processing yield parameters could not be related with the dietary parameters. The low diets, which have similar protein contents to those used in some integrations, were shown to produce poor responses and, therefore are not recommended for broilers from 1 to 40 days of age. Alternating low and high ideal protein profiles at 21 days could result in similar feed conversions, and therefore, can lead to production cost reduction.
amino acids; carcass; digestible lysine; performance; strain crosses
