Performance and carcass characteristics of Cobb × Cobb 500 slow-feathering male broilers fed on dietary programs having stepwise increases in ideal protein density

The Cobb × Cobb 500 slow-feathering male is a fast early-growth broiler grown under variable feeding programs and amino acid (AA) densities. An experiment was conducted using diets with increased ideal protein densities in a feeding program of 1 to 7 d, 8 to 21 d, 22 to 35d, and 36 to 42 d. Diets had ratios between essential digestible (D) AA and DLys (DAA:DLys) as follows: TSAA, 75%; DThr, 65%; DVal, 75% (from 1 to 7 d) and 77% (from 8 to 42 d); DIle, 67%; DArg, 104%; and DTrp, 17%. A completely randomized experimental design in a 3 × 3 factorial arrangement of 3 AA densities (low, moderate, and high) from 1 to 21 d (phase I) and 3 AA densities from 22 to 42 d (phase II) was used. The moderate dietary program was set with DLys at 1.26, 1.15, 1.05, and 0.95% from the prestarter to finisher phase. Replications per treatment were 30 from 1 to 21 d and 10 from 22 to 42 d. Birds fed the high-AA-density diets in phase I had the best BW gain at 35 and 42 d (P < 0.05) and the lowest FCR (P < 0.05) when combined with the high- or moderate-AA-density diets in phase II. The high- and moderate-AA-density diets in phase I maximized BW gain at 42 d when combined with either the high- or moderate-AA-density diet in phase II (P < 0.05). Percentages of breast fillets, breast tenders, and thighs were not affected by treatment in phase I; however, breast fillet percentage was maximized with when the moderate- or high-AA-density diets (P < 0.05) were fed in phase II, whereas breast tenders and thighs were maximized only when the high-AA-density diets (P < 0.01) were fed in phase II. Commercial application will depend on ingredient costs and meat market prices at decision time based on the program that results in the lowest cost per sellable product.