Dietary Levels and Ratio of Methionine and Cystine for Maximum Performance of Broilers.

Abstract

Four experiments were conducted to estimate the total sulfur amino acid (TSAA) level for maximum growth performance (requirement) of broilers, to elucidate whether methionine (Met) requirements were affected by TSAA levels, and to confirm whether excessive Met and cystine (Cys) had a negative effect on the performance of broilers. Eight-day-old Arbor Acres strain female chicks were kept individually in wire cages, and fed practical type experimental diets ad libitum for 10 days. Experimental diets were consisted of corn and soybean meal, and contained 3, 200 kcal metabolizable energy/kg of diet, and 16 to 17% crude protein. When essential amino acids, except for TSAA, derived from feedstuffs were less than 95% of NRC requirements, crystalline amino acids were added.In Experiment 1, to determine the Met requirement at various dietary TSAA levels, Met with 5 graded levels from 0 to 0.80% was added to the diet containing 0.25% Met and 0.22% Cys. In Experiments 2 and 3, to clarify the optimum Met ratio to Cys, Met was added with 5 graded levels by balancing Cys to diets slightly deficient (0.60%), adequate (0.67%), slightly excess (0.74%) and excess (1.30%) in TSAA. In Experiment 4, to clarfy the role of Cys, Cys with 4 graded levels from 0.10 to 1.00% was added to the 0.30% Met and 0.30% Cys diet. As negative control, 1.90% Met diet was reported.From the results obtained, it was suggested that 0.66% of TSAA was required for the maximum growth performance of broilers from 8 to 18 days of age, and 0.30% of Met was required irrespective of dietary TSAA levels. This meant that the ratio of Met replaced by Cys increased with increasing TSAA levels. When the dietary Met level exceeded 0.7%, the excessive Met caused the depression of growth performance of broilers. However, no negative effects were observed even when the dietary Cys was at 1.90% of diet.