The current study evaluated the formulation of broiler diets containing cottonseed meal (CSM) on a total amino acid versus a digestible amino acid basis with two different digestible lysine requirements. Male broiler chicks were allotted to 20 treatments with four replicates of six male chicks per replicate in a completely randomized block design in a factorial arrangement with three factors (2 levels of digestible lysine requirement x 2 amino acid formulation basis x 5 levels of cottonseed meal). The first of the twenty treatments was the corn-SBM control diet based on digestible lysine requirement for maximum body weight gain. Diets 1 to 5 contained 0, 5, 10, 15 or 20% CSM, respectively and were formulated to contain levels of total AA equivalent to those in the first treatment. Diets 6 to 10 contained the same levels of CSM as diets 1 to 5 but were formulated to be equal in digestible AA content to the first treatment. Treatments 11 to 20 were the same as treatments 1 to 10 but on the basis of digestible lysine requirement for maximum feed efficiency. Control diet met an ideal amino acid ratio recommended by Illinois 2000 for all other indispensable amino acids for chicks 0 to 21-d old as determined for the levels of 1.075 and 1.179% digestible lysine. Feed and water were supplied ad libitum and uniform light was provided 24h daily. Diets were formulated based on analyzed values. Digestible amino acids were calculated using digestibility coefficients of Rhone-Poulenc (1993) and by assuming 100% digestibility of crystalline amino acids. Results indicated that Dietary inclusion of 10 to 20% CSM on a total AA and weight gain lysine requirement basis depressed chick weight gain and feed efficiency (P<0.01) in comparison to the corn-SBM control diet. However when the diets were formulated according to the requirement for maximum feed efficiency, dietary inclusion of 20% CSM on a total AA basis depressed chick weight gain and feed efficiency in comparison to the corn-SBM control diet (P<0.01). In both cases, formulating diets containing CSM on a digestible AA basis improved chick performance as compared to that achieved from formulation on a total AA basis (P<0.01). No significant effects of cottonseed meal level, digestible lysine requirement and amino acid formulation basis were observed on the average daily feed intake. Dietary formulation on the basis of lysine requirement for maximum feed efficiency vs the maximum weight gain had no effect on average body weight gain and feed efficiency, but numerically resulted in 1.1% improvement in feed efficiency. No significant interaction was observed between cottonseed level and amino acid formulation basis on chick performance.
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