Early Growth Response of Broilers to Dietary Lysine at Fixed Ratio to Crude Protein and Essential Amino Acids

The effects of dietary lysine (Lys) at a fixed ratio to crude protein (CP) and essential amino acids (EAA) on early growth response of broilers were studied. Four diets were formulated to contain similar metabolizable energy (ME, 2,950 kcal/kg) but contained graded levels of incremental Lys (1.1, 1.2, 1.3 and 1.4%) while also increasing the dietary CP and EAA (methionine, methionine+ cystine, threonine and tryptophan) to maintain a constant ratio with Lys. Each diet was fed at random to 10 replicates of 6 chicks each throughout the experimental period (1-21 d). At the lowest concentration of Lys of 1.1% (19.04% CP), body weight gain (BWG) was lowest and feed conversion ratio (FCR) was poorest. The BWG increased and FCR decreased linearly as dietary Lys increased upto 1.3% (22.5% CP). Lowest feed consumption was observed in the dietary group that contained 1.1% Lys (19.04% CP) in the diet. Increasing the concentration of Lys to 1.2% (20.77% CP), significantly increased the feed consumption. The concentrations of protein, calcium, phosphorus and cholesterol in serum were not influenced by the variation in Lys contents in the diet. The humoral immune response as measured by antibody titre in response to SRBC inoculation was significantly lower in the diets containing 1.1% Lys compared to 1.4%. It is concluded that the Lys requirement of broilers is 1.3% (22.5% CP) during 0 to 21 days of age for eliciting optimum performance when a fixed ratio of Lys to CP (1:17.31) and essential AA is maintained (1:0.47 Met; 1:0.56 Thr; 1:0.17 Try). (