Titration of dietary isoleucine and evaluation of branched-chain amino acid levels in female Cobb 500 broilers during a 22- to 42-day finisher period

Recent research into the branched-chain amino acids has indicated that broiler responses to dietary isoleucine may vary from classic data. Current isoleucine data has focused on male broilers leaving a gap in the literature for female data. An experiment was conducted to determine the isoleucine requirements for a 22 to 42 day finisher period in Cobb MV × 500 female broilers. A basal diet was formulated to contain dietary isoleucine, valine, and leucine to lysine ratios of 56, 78, and 135, respectively, and graded amounts of L-isoleucine were added to achieve isoleucine to lysine ratios of 56, 59, 62, 65, 68, 71, and 74. An additional external control diet was formulated with isoleucine, valine, and leucine to lysine ratios of 65, 72, and 135, respectively, to which aliquots of L-isoleucine, L-valine, and L-leucine were added to create diets containing isoleucine, valine, and leucine ratios ranging from 65 to 71, 72 to 81, and 135 to 175, respectively. Digestible lysine was maintained at 1.10 percent. Linear responses were observed for day 42 BW, BW gain, feed conversion, fat pad yield, and breast yield. No other significant responses were observed for the isoleucine titrations. Comparison among the external controls generated a significant decrease in fat pad yield when all 3 branched-chain amino acids were increased compared to birds fed the 65 isoleucine to lysine diet. The linear response observed for both feed conversion and breast meat yield indicate that optimal isoleucine levels may be beyond the 74 isoleucine to lysine ratio tested in this study.