Dietary isoleucine responses in male broiler chickens.

1. Three experiments were conducted to measure growth and carcase responses of growing and finishing broilers fed on test diets formulated to be deficient in isoleucine (Ile). 2. Dose titration methodology was used to measure growth and carcase responses of growing and finishing broilers to graduations of Ile in three additional experiments. 3. The experiments were conducted from d 18 to 30, 30 to 42, and 42 to 56. 4. Broilers given Ile-deficient test diets had poorer weight gain, feed conversion and carcase responses than broilers fed on Ile test diets containing a surfeit of Ile. Adding supplemental Ile to the test diet resulted in equivalent growth and carcase responses to those of broilers fed on the control diet with equal Ile from intact protein sources. 5. Recommended total Ile needs varied between 6.7 and 7.1 g/kg from d 18 to 30, 6.4 to 6.6 g/kg from d 30 to 42, and 5.5 to 6.6 g/kg from d 42 to 56.