Determining the optimal digestible isoleucine to lysine ratio of Ross 708 × Ross YP male broilers from 14 to 28 days of age

Previous research within our laboratory determined the optimal male Ross 708 dIle:dLys ratio for the starter phase to be greater than recent breeder recommendations (70 vs. 67%). Thus, the current objective was to assess the subsequent growth phase (grower) in order to evaluate the optimal dIle:dLys ratio for maximized growth performance of Ross 708 × Ross YP male broilers. On d of hatch, 2,400 chicks were equally allocated to 96 pens and fed a common starter diet. On d 14, pen weights were equalized by block (12 replications/treatments). Experimental grower diets (d 14–28) were created from a common Deficient (53% dIle:dLys) corn and soybean meal-based diet. After batching, half of the Deficient diet was used to create the Summit diet (83% dIle:dLys). The remaining 5 experimental diets ranged from 58 to 78% dIle:dLys and were blended proportions of the Deficient and Summit diets. A practical control diet (PRAC-CON; 68% dIle:dLys) was manufactured separately to verify the blended control diet (BLEND-CON; 68% dIle:dLys). All dIle:dLys ratios were estimated using quadratic regression (QR; 95% of the asymptote), as well as linear and quadratic broken line models (LBL; QBL). Based on the current data and using multiple regression models the estimated ratios ranged from 62 to 68% for BW and BWG, and 67-70% for FCR and are similar to the current breeder nutrient specifications for the grower phase. Further research should evaluate dIle:dLys requirements of male Ross 708 × Ross YP broilers during the remaining grow-out phases.