Effect of different digestible isoleucine/lysine ratios for broiler chickens

Two experiments were conducted to evaluate different digestible isoleucine/lysine ratios on diets for broiler chickens in the starter (7 to 21 days) and finishing (30 to 43 days) phases. For the tests, the experimental design was of randomized blocks with seven treatments (six different digestible isoleucine/lysine ratios and a control treatment) and eight repetitions of 25 and 20 birds (COBB males) per experimental unit in the starter and finishing phases, respectively. The diets met the requirements, except for isoleucine and lysine. To avoid excess lysine in the experimental diets, the digestible lysine content was calculated to be 87% and 89% of the recommended for the starter and finishing phases, respectively. The control treatment was adequate in lysine and isoleucine. Feed intake, weight gain, feed conversion and carcass yield in the two phases were evaluated. There was quadratic effect of different ratios on feed intake in the finishing phase and on weight gain and feed conversion rate in both phases. There was quadratic effect on breast meat yield and breast fillets in the starter phase, but there was no significant effect on carcass yield in the finishing phase. The digestible isoleucine/lysine ratio recommended for broilers in the starter phase (7 to 21 days) is 66% and for the finishing phase (30 to 43 days), it is 68%.