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Determination of dietary digestible valine:lysine ratio for Cobb MV × 500 male and female broilers from 15 to 35 d of age

Maynard, C., S. Liu, J. Lee, J. Caldas, E. Diehl, S. Rochell and M. Kidd

Knowledge of dietary Val needs in commercial broilers is paramount for least cost diets and performance efficiencies as Val is typically the fourth limiting amino acid in diets based on cereals and oilseeds. Two concurrent studies were conducted to determine Val:Lys ratios needed for optimal performance and carcass traits for male (Exp 1) and female (Exp 2) broilers during 15 to 35 d of age. Two diets were formulated: a corn and soybean meal control and a valine deficient corn and soybean meal diet. Aliquots of L-Val were then added to the Val deficient diet, producing diets with Val:Lys ratios of 57, 64, 71, 78, 85, and 92. An additional diet was created using the titration diet with a Val:Lys ratio of 78 and an increased Ile:Lys ratio of 66 to 70. All diets were formulated to be equal in ME (3,100 kcal/kg diet) and Lys (1.06% digestible of diet). Diets were fed to 6 replicate pens of 21 birds in both Exp. Gain of BW, feed intake, and feed conversion ratio were determined for the 15 to 35 d period, and carcass traits and breast meat quality were evaluated on d 36. All data were analyzed by regression analysis and requirements were estimated at 95% of the quadratic response to prevent overestimation. In both Exp, the control diet performed better than the comparable titration diet with a 78 Val:Lys ratio. In Exp 1, no liner, quadratic, or cubic response was observed for any live performance measurement or carcass yield except a cubic response for feed conversion ratio. Increasing the Ile:Lys ratio in Exp 1 resulted in a decrease (P=0.033) in total breast yield of 0.88 percentage units. The male Val:Lys ratio requirement for feed conversion was estimated to be 78. In Exp 2, BW gain linearly increased as Val:Lys ratio increased. Similar to that observed in Exp 1, a cubic response to the Val:Lys ratio was observed for feed conversion, with no response for any processing yield. Digestible Val:Lys ratio did not impact the occurrence or severity of woody breast in either Exp. The female Val:Lys ratio needed for feed conversion was estimated to be 77.

Results from this study indicate that formulating diets to contain a Val:Lys ratio of 78 is adequate to produce good performance for both male and female broilers.