M. Zaghari - Department of Animal Science, College of Agriculture, University of Tehran, Karaj, Islamic Republic of Iran.
M. Shivazad - Department of Animal Science, College of Agriculture, University of Tehran, Karaj, Islamic Republic of Iran.
A. Kamyab - Department of Animal Science, College of Agriculture, University of Tehran, Karaj, Islamic Republic of Iran.
A. Nikkhah - Department of Animal Science, College of Agriculture, University of Tehran, Karaj, Islamic Republic of Iran.

An experiment was conducted to reevaluate the digestible lysine requirement of Arian male broilers by comparing the performance of chicks fed different levels of cottonseed meal (CSM) on a total amino acid (AA) versus a digestible AA basis. Four hundred and thirty two (۴۳۲) Arian male broiler chicks were allotted to ۱۸ treatments with four repli-cates of six chicks each in a completely randomized block design in a factorial arrange-ment with two factors (two levels of digestible lysine  nine different diets). The first of the eighteen treatments was the corn and soybean meal control diet based on previously de-termined digestible lysine requirement for maximum body weight gain. Diets ۲ to ۵ con-tained ۵, ۱۰, ۱۵ or ۲۰% CSM, respectively and were formulated to contain levels of total AA equivalent to those in the first treatment. Diets ۶ to ۹ contained the same levels of CSM as diets ۲ to ۵ but the diets were formulated to be equal in digestible AA content to the first treatment. Treatments ۱۰ to ۱۸ were the same as treatments ۱ to ۹, but on the ba-sis of determined digestible lysine requirement for maximum feed efficiency. Formulating diets containing CSM on a digestible AA basis resulted in an improvement in chick per-formance compared to those formulated on a total AA basis (P<۰.۰۱). The lessening of chick performance with diets formulated on a total AA basis compared to a digestible AA basis, indicated that the previously determined digestible lysine requirement for the Arian broiler strain may be correct.

Broiler, Corn-soybean meal, Cottonseed meal, Digestible amino acid, Total amino acid