Digestible lysine requirement of broilers based on practical diet

Abstract

The aim of this study was to estimate the requirement for digestible lysine for broilers from 35 to 49 days of age. Two hundred and forty chicks with a mean weight of 44±1 g were used in a completely randomized design, made up of male and female chicks and 6 digestible lysine levels. Experimental diets were formulated to be isoenergetic and isonitrogenous. Fitted broken lines on different responses indicated break points at 0.93, 0.93 (for body weight), 0.98, and 0.92 for feed conversion ratio for male and female, respectively. The results showed that the digestible lysine requirement of male broilers for maximum breast yield percentage, plasma free lysine and antibody titer against Newcastle disease virus exceeded the range of lysine levels tested. Dietary lysine had a significant effect in increasing the plasma free lysine, albumin, total protein, immunoglobulin, antibody titer against sheep red blood cell, Newcastle disease virus and heterophil to lymphocyte ratio. In conclusion, lysine requirements of broilers for performance were lower than breast yield percentage and immune responses. Broken-line analysis showed that the concentrations of plasma free lysine were useful physiological indicators for determining the digestible lysine requirement of male and female broilers. Our results suggest that the estimated requirements based on exponential response curves were higher than estimated requirements obtained using a broken-line model.