performance of broiler chicks fed cottonseed and soybean meal based diets and determination of the optimum supplemental lysine in starts period

an experiment was conducted to determine the optimal level of supplemental lysine in a corn-soybean mealcottonseed meal starter diet. three hundred and sixty day-old male chicks (ross 308) were used in a completely randomized design (15 birds per each pen). a basal diet was formulated to meet or exceed nrc (1994) recommendations except for lysine. graded levels of supplemental lysine (0, 0.1, 0.2, 0.3, 0.4, and 0.5% of diet) were added to the basal diet at the expense of corn starch. at 14d of age, performance and carcass attributes including body weight gain (bgw), feed conversion ratio (fcr), feed intake (fi), breast meat yield (bmy), and thigh yield (ty) were assessed. the results showed that lysine supplementation significantly improved bgw, fcr, fi, bmy, and ty. to determine the optimum level of supplemental lysine, modeling approach was applied and inflection point in spline models was considered as an optimum point. using linear broken-line model, inflection points for bwg, fc, bmy, ty were 0.24, 0.26, 0.35, and 0.22% of diet, respectively. these values in quadratic broken-line model were 0.39, 0.15, 0.52, and 0.33% of diet, respectively. in conclusion, the usage of cottonseed meal in starting broiler chicks may increase the needed supplemental lysine in the diet due to low amino acid digestibility of cottonseed meal. although the optimum level of supplemental lysine depends on response criteria and statistical model, required supplemental lysine for bmy was higher than others.