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

An experiment was conducted to determine the dietary digestible lysine requirement of male and female broiler chickens (Arian) during the period from ۶ to ۲۱ days post-hatching. An amino acid-fortified basal diet containing corn and soybean meal as intact protein sources provided ۲۰ % CP, and ۳۲۰۰ kcal AMEn / kg. In this experiment ۱۵۰ male and ۱۵۰ female chicks were allocated on the basis of BW to ۱۲ treatments in a factorial arrangement (two sexes at six digestible lysine levels) with five replications of five chicks each in a completely randomized design (CRD). The digestible lysine levels fed were ۰.۸۵, ۰.۹۵, ۱.۰۵, ۱.۱۵, ۱.۲۵ and ۱.۳۵%. The growth rate and feed efficiency of birds fed the basal diet fortified with a surfeit level of l-Lysine-HCl were equal to those of birds fed a corn-soybean meal positive control diet. Average body-weight gain (ABWG) and gain: feed (GF) responded quadratically (P<۰.۰۵) to incremental dietary lysine addition. Subjecting the growth data to broken-line analysis indicated that the digestible lysine requirement for maximum body weight gain was ۱.۰۷۵% for males and ۱.۰۴۹% for females. The lysine requirement for maximum feed efficiency was ۱.۱۷۹% for males and ۱.۱۴۹% for females. Male chicks required a higher level of dietary lysine than females for both maximal ABWG and GF. Regardless of sex, ۸.۸% more digestible lysine (percentage of diet) was required for maximal GF than that needed for maximal ABWG.

Digestible amino acid, Broiler chickens, Lysine requirement