Maximizing the performance of heat stressed broilers by optimizing starch-to-lipid ratios, digestible amino acid, and metabolizable energy during the finisher phase

This study investigated the effects and interactions among diets formulated to have high starch-to-lipid ratios (S:L), amino acid density [indicated as % digestible lysine (DigLys)], and AME on growth performance and carcass characteristics of heat stressed broilers. A {3,3} simplex lattice design was used to assess relative effects and generate predictive models. Three basal finisher diets were formulated to have the highest S:L ratio (Basal A; 20:1), DigLys (Basal B; 1.30 %), or AME (Basal C; 3300 kcal/kg). These diets were blended at levels of 0.00, 0.33, 0.67, or 1.00 to produce 10 finisher diets. The mixtures allowed varying S:L ratios (4:1 to 20:1), DigLys (0.80 to 1.30 %), and AME (2800 to 3300 kcal/kg) content of diets. sex-separated (n = 6,864) Ross 708 broiler chicks were placed in separate rooms (5 male and 4 female) with a pen stocking density of 31 kg/m². Sex-specific starter and grower diets were fed until d 21. The rooms were maintained at 21°C during d 21 to 27. From d 27 to 32, the birds were subjected to cyclical heat stress, with 12 h of 31°C followed by 12 h of 21°C, with a minimum RH of 50 %. BW and feed residual weights were measured on d 21, 27, and 32, then used to calculate BW gain (BWG) and feed-to-gain ratios (F:G). On d 33, 20 birds per treatment per sex were slaughtered to determine carcass characteristics. Under these conditions (d 21 to 32), maximum male BWG of 926 g was estimated to occur when fed a diet comprised of 42.2 % Basal B and 57.8 % Basal C with a S:L ratio of 4:1, AME of 3089 kcal/kg, and 1.01 % DigLys. Diet did not influence female BWG during heat stress. Although a practical recommendation was not possible for optimal breast meat yield (% live weight) and F:G ratios, the results, indicated that increasing DigLys would improve these parameters under heat stress.