One thousand eighthundred and ninety male broilers of two strain crosses (fast and slow initialgrowth) 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-soybeanmeal feeds were formulated to maintain the Met+Cys:Lys and Thr:Lys relationshipsat 75 and 65%, respectively, on true digestible basis. Three ideal protein profileswere used: low, medium and high. From 1 to 21 days of age, half of the birdsfed low and high diets were changed to high and low diets, respectively. Birdson the medium diet were kept on the same diet until the end of the study. A3 × 2 (ideal protein profile x strain cross) factorial design was usedfor the period from 1 to 21 days and a 5 × 2 design thereafter. Carcassand commercial cuts were performed at 34 and 40 days of age to determine correspondinglive weight and carcass yields. In general, the fast strain growth was superiorin comparison to the low one when live performance and carcass and commercialcuts were evaluated. Live performance was positively affected by the increasesin the dietary protein profiles; however, processing yield parameters couldnot be related with the dietary parameters. The low diets, which have similarprotein contents to those used in some integrations, were shown to produce poorresponses and, therefore are not recommended for broilers from 1 to 40 daysof age. Alternating low and high ideal protein profiles at 21 days could resultin similar feed conversions, and therefore, can lead to production cost reduction.
