Effect of conditioning temperature and retention time on pellet quality, ileal digestibility, and growth performance of broiler chickens

Eight broiler chicken diets were produced by using 2 pellet conditioning temperatures (65 and 85 degrees C) and 4 pellet retention times in the conditioner (3, 9, 14, and 20 s). The effect of dietary treatments on pellet physical quality (intact pellet percentage, pellet hardness, pellet durability index, and water activity), growth performance (0 to 21 and 0 to 42 d), apparent ileal digestibility (CAID) of dry matter, crude protein and starch, and ileal digestible energy (IDE) was evaluated. 1,536 broiler chickens were randomly assigned to 8 dietary treatments (8 replicates of 24 chickens each). On d 42, 2 chickens per replicate were randomly selected for ileal content collection to evaluate dietary CAID and IDE. The greater conditioning temperature (85 degrees C) improved pellet percentage, durability, and hardness (P < 0.001), and promoted greater feed intake, but also increased feed conversion by 1.2% (0 to 42 d, P < 0.05). The retention time of 20 s enhanced both weight gain and feed conversion (P < 0.05). Multiple interactions were observed for digestibility traits (P < 0.001). At 65 degrees C, CAID of dry matter, crude protein and starch, and IDE increased with longer retention times. However, all digestibility coefficients and IDE decreased when diet was conditioned at 85 degrees C and retained for more than 9 s. In conclusion, conditioning at 85 degrees C with longer retention times improved pellet physical quality, but reduced digestibility traits and growth performance of broiler chickens. However, conditioning at 65 degrees C with retention times shorter than 14 s also had detrimental effects on ileal nutrient digestibility, digestible energy, and growth performance.